阅读说明：本技术 图像传感器 (Image sensor with a plurality of pixels ) 是由 沈殷燮 于 2020-03-20 设计创作，主要内容包括：一种图像传感器,包括：像素阵列,所述像素阵列包括连接到多条行线和多条列线的多个像素,所述多个像素中的每一个像素包括用于响应于光而产生电荷的光电二极管和具有用于存储所述电荷的浮置扩散的像素电路；以及控制器,所述控制器被配置为在第一时间周期期间将所述浮置扩散的电容调整为第一值,并且从所述像素电路获得第一像素信号,在所述第一时间周期之后的第二时间周期期间将所述浮置扩散的电容调整为大于所述第一值的第二值,并且从所述像素电路获得第二像素信号,并且使用所述第一像素信号和所述第二像素信号生成结果图像。(An image sensor, comprising: a pixel array comprising a plurality of pixels connected to a plurality of row lines and a plurality of column lines, each of the plurality of pixels comprising a photodiode for generating charge in response to light and a pixel circuit having a floating diffusion for storing the charge; and a controller configured to adjust the capacitance of the floating diffusion to a first value during a first time period and obtain a first pixel signal from the pixel circuit, to adjust the capacitance of the floating diffusion to a second value greater than the first value during a second time period after the first time period and obtain a second pixel signal from the pixel circuit and generate a resultant image using the first pixel signal and the second pixel signal.)

1. An image sensor, comprising:

a pixel array comprising a plurality of pixels connected to a plurality of row lines and a plurality of column lines, each of the plurality of pixels comprising a photodiode for generating charge in response to light and a pixel circuit having a floating diffusion for storing the charge; and

a controller configured to adjust a capacitance of the floating diffusion to a first value during a first time period and obtain a first pixel signal from the pixel circuit, to adjust the capacitance of the floating diffusion to a second value greater than the first value during a second time period after the first time period and obtain a second pixel signal from the pixel circuit and generate a resultant image using the first pixel signal and the second pixel signal.

2. The image sensor of claim 1, wherein the controller drives the plurality of row lines according to a frame period, and the first time period or the second time period is included in the frame period, and

wherein the controller generates a first image frame using the first pixel signal, generates a second image frame using the second pixel signal, and generates the result image using the first image frame and the second image frame.

3. The image sensor of claim 2, wherein the photodiode generates charge upon exposure during a first exposure time included in the first time period and generates charge upon exposure during a second exposure time included in the second time period, and the second exposure time is shorter than the first exposure time.

4. The image sensor of claim 3, wherein the controller adjusts the capacitance of the floating diffusion to a third value greater than the first value and obtains a third pixel signal from the pixel circuit during a third time period after the second time period, and generates a third image frame using the third pixel signal.

5. The image sensor of claim 4, wherein the photodiode generates a charge when exposed during a third exposure time of the third time period, and the third exposure time is shorter than the second exposure time.

6. The image sensor of claim 4, wherein the controller generates the result image using the first image frame, the second image frame, and the third image frame.

7. The image sensor of claim 4, wherein the second value and the third value are substantially the same.

8. The image sensor of claim 2, wherein the first time period comprises a first sub-time period and a second sub-time period subsequent to the first sub-time period, and

wherein the controller adjusts the capacitance of the floating diffusion to the first value during the first sub-time period and obtains a first sub-pixel signal from the pixel circuit, adjusts the capacitance of the floating diffusion to a value greater than the first value during the second sub-time period and obtains a second sub-pixel signal from the pixel circuit, and generates the first image frame using the first and second sub-pixel signals.

9. The image sensor of claim 8, wherein the controller adjusts the capacitance of the floating diffusion to the second value during the second sub-time period.

10. The image sensor of claim 1, wherein the controller drives a selected row line of the plurality of row lines in each scan period, and the first time period and the second time period are included in one of the scan periods.

11. The image sensor of claim 10 wherein the controller obtains a first reset voltage and a first pixel voltage from each pixel connected to the selected row line during the first time period and obtains a second reset voltage and a second pixel voltage from each pixel connected to the selected row line during the second time period.

12. The image sensor of claim 10 wherein the photodiode included in each pixel connected to the selected row line generates a first charge in response to light during a first exposure time of the first time period and a second charge in response to light during a second exposure time of the second time period, and

wherein the second exposure time is shorter than the first exposure time.

13. The image sensor of claim 10, wherein the one of the scan periods further comprises a third time period after the second time period, and

wherein the controller adjusts a capacitance of the floating diffusion included in each pixel connected to the selected row line to a third value greater than the first value during the third time period, and obtains a third reset voltage and a third pixel voltage from each pixel connected to the selected row line.

14. The image sensor of claim 13, wherein the second value and the third value are substantially the same.

15. The image sensor of claim 10, wherein the first time period comprises a first sub-time period and a second sub-time period subsequent to the first sub-time period, and

wherein the controller adjusts the capacitance of the floating diffusion included in each pixel connected to the selected row line to the first value during the first sub-time period, and adjusts the capacitance of the floating diffusion included in each pixel connected to the selected row line to a value greater than the first value during the second sub-time period.

16. The image sensor of claim 15 wherein the controller sequentially obtains a first sub-reset voltage and a first sub-pixel voltage from each pixel connected to the selected row line during the first sub-time period, and sequentially obtains a second sub-pixel voltage and a second sub-reset voltage from each pixel connected to the selected row line during the second sub-time period.

17. The image sensor of claim 1, wherein each of the plurality of pixels further comprises a reset transistor connected between a power supply node for providing a power supply voltage and the floating diffusion and a switching device connected between the reset transistor and the floating diffusion, and

wherein the controller adjusts the capacitance of the floating diffusion by turning on or off the switching device.

18. An image sensor, comprising:

a photodiode for generating charge in response to light during an exposure time;

a floating diffusion for storing the charge;

a reset transistor connected between a power supply node for supplying a power supply voltage and the floating diffusion; and

a switching device connected between the reset transistor and the floating diffusion,

wherein the switching device is turned off when the exposure time is longer than a reference time, and the switching device is turned on when the exposure time is shorter than the reference time.

19. The image sensor of claim 18, wherein the capacitance of the floating diffusion increases when the switching device is on and decreases when the switching device is off.

20. An image sensor, comprising:

a pixel array including a plurality of pixels, each of the plurality of pixels including a photodiode and a pixel circuit that outputs a reset voltage and a pixel voltage using charges generated from the photodiode; and

a controller configured to adjust a conversion gain of the pixel circuit according to an exposure time of the photodiode while the pixel circuit outputs the reset voltage and the pixel voltage,

wherein the controller generates a result image using a first reset voltage and a first pixel voltage output from the pixel circuit when the conversion gain is a first value, and generates a result image using a second reset voltage and a second pixel voltage output from the pixel circuit when the conversion gain is a second value different from the first value.

Technical Field

Exemplary embodiments of the inventive concept relate to an image sensor.

Background

Image sensors are semiconductor-based sensors that receive light and produce an electrical signal. For example, an image sensor converts light into an electrical signal that conveys information used to make an image. The image sensor may include a pixel array having a plurality of pixels, a logic circuit for driving the pixel array and generating an image, and the like. The plurality of pixels may include photodiodes for generating charges by reacting to external light, pixel circuits for converting the charges generated by the photodiodes into electrical signals, and the like. Image sensors have been conventionally used in cameras for capturing still images and video images, but are now widely used in smart phones, tablet Personal Computers (PCs), laptop computers, televisions, vehicles, and the like. Recently, various methods for solving noise characteristics of the image sensor and improving a dynamic range, etc. have been developed.

Disclosure of Invention

According to an exemplary embodiment of the inventive concept, there is provided an image sensor including: a pixel array comprising a plurality of pixels connected to a plurality of row lines and a plurality of column lines, each of the plurality of pixels comprising a photodiode for generating charge in response to light and a pixel circuit having a floating diffusion for storing the charge; and a controller configured to adjust the capacitance of the floating diffusion to a first value during a first time period and obtain a first pixel signal from the pixel circuit, to adjust the capacitance of the floating diffusion to a second value greater than the first value during a second time period after the first time period and obtain a second pixel signal from the pixel circuit and generate a resultant image using the first pixel signal and the second pixel signal.

According to an exemplary embodiment of the inventive concept, there is provided an image sensor including: a photodiode for generating charge in response to light during an exposure time; a floating diffusion for storing the charge; a reset transistor connected between a power supply node for supplying a power supply voltage and the floating diffusion; and a switching device connected between the reset transistor and the floating diffusion, wherein the switching device is turned off when the exposure time is longer than a reference time, and turned on when the exposure time is shorter than the reference time.

According to an exemplary embodiment of the inventive concept, there is provided an image sensor including: a pixel array including a plurality of pixels, each of the plurality of pixels including a photodiode and a pixel circuit for outputting a reset voltage and a pixel voltage using charges generated from the photodiode; and a controller configured to adjust a conversion gain of the pixel circuit according to an exposure time of the photodiode when the pixel circuit outputs the reset voltage and the pixel voltage, wherein the controller generates a result image using a first reset voltage and a first pixel voltage output from the pixel circuit when the conversion gain is a first value, and generates the result image using a second reset voltage and a second pixel voltage output from the pixel circuit when the conversion gain is a second value different from the first value.

Drawings

The above and other features of the present inventive concept will be more clearly understood by describing in detail exemplary embodiments thereof with reference to the attached drawings, in which:

fig. 1 is a block diagram illustrating an image sensor according to an exemplary embodiment of the inventive concept;

fig. 2 and 3 are diagrams illustrating an image sensor according to an exemplary embodiment of the inventive concept;

fig. 4 is a diagram illustrating an operation of an image sensor according to an exemplary embodiment of the inventive concept;

fig. 5 is a circuit diagram illustrating a pixel included in an image sensor according to an exemplary embodiment of the inventive concept;

fig. 6 is a diagram illustrating an operation of adjusting a conversion gain of a pixel in an image sensor according to an exemplary embodiment of the inventive concept;

fig. 7 is a diagram illustrating an operation of an image sensor according to an exemplary embodiment of the inventive concept;

fig. 8 and 9 are diagrams illustrating an operation of an image sensor according to an exemplary embodiment of the inventive concept;

fig. 10 is a diagram illustrating an operation of an image sensor according to an exemplary embodiment of the inventive concept;

fig. 11 and 12 are diagrams illustrating an operation of an image sensor according to an exemplary embodiment of the inventive concept;

fig. 13 is a diagram illustrating an operation of an image sensor according to an exemplary embodiment of the inventive concept;

fig. 14 and 15 are diagrams illustrating an operation of an image sensor according to an exemplary embodiment of the inventive concept;

fig. 16 is a diagram illustrating an operation of an image sensor according to an exemplary embodiment of the inventive concept;

fig. 17 and 18 are diagrams illustrating an operation of an image sensor according to an exemplary embodiment of the inventive concept;

fig. 19A and 19B are graphs illustrating an operation of an image sensor according to an exemplary embodiment of the inventive concept;

fig. 20 and 21 are diagrams illustrating an operation of an image sensor according to an exemplary embodiment of the inventive concept;

fig. 22 is a diagram illustrating a pixel array of an image sensor according to an exemplary embodiment of the inventive concept;

fig. 23 is a circuit diagram illustrating a pixel circuit of an image sensor according to an exemplary embodiment of the inventive concept;

fig. 24 and 25 are diagrams illustrating an operation of an image sensor according to an exemplary embodiment of the inventive concept; and

fig. 26 is a block diagram illustrating an electronic device including an image sensor according to an exemplary embodiment of the inventive concept.

Detailed Description

Hereinafter, exemplary embodiments of the inventive concept will be described with reference to the accompanying drawings. In the drawings, like reference numerals may denote like elements.

Fig. 1 is a block diagram illustrating an image sensor according to an exemplary embodiment of the inventive concept.

Referring to fig. 1, an image sensor 100 in the present embodiment may include a pixel array 110 and a controller 120. The controller 120 may include a row driver 121, readout circuitry 122, a column driver 123, control logic 124, and the like.

The image sensor 100 may convert light received from an external source into an electrical signal, and may generate image data. The pixel array 110 included in the image sensor 100 may include a plurality of pixels PX. The plurality of pixels PX may include a photoelectric device for receiving light and generating charges. The optoelectronic device may be, for example, a Photodiode (PD). The plurality of pixels PX may be connected to a plurality of row lines extending in the first direction and a plurality of column lines extending in the second direction. In an exemplary embodiment of the inventive concept, each of the plurality of pixels PX may include two or more photodiodes. Each of the plurality of pixels PX may include two or more photodiodes to generate pixel signals corresponding to various colors of light or to provide an auto-focusing function.

Each of the plurality of pixels PX may include a pixel circuit for generating a pixel signal from charges generated from the photodiode. As an example, the pixel circuit may include a transfer transistor, a drive transistor, a select transistor, a reset transistor, a floating diffusion (in general, the expression "floating diffusion" may refer to a "floating diffusion portion" or "floating diffusion region"), and the like. The pixel circuit may output a reset voltage and a pixel voltage. The pixel voltage may correspond to charges generated from a photodiode included in each of the plurality of pixels PX and stored in a floating diffusion. In an exemplary embodiment of the inventive concept, two or more adjacent pixels PX may form a single pixel group, and two or more pixels PX included in the pixel group may share at least one of a transfer transistor, a driving transistor, a selection transistor, and a reset transistor.

In an exemplary embodiment of the inventive concept, a capacitance of a floating diffusion included in a pixel circuit may be adjusted. As an example, the capacitance of the floating diffusion may be adjusted according to the length of exposure time of the pixel PX exposure. Therefore, when the charges stored in the floating diffusion are converted into voltages, a conversion gain suitable for an exposure time can be applied. In this case, noise characteristics, dynamic range, and the like of the image sensor 100 can be improved.

The row driver 121 may drive the pixel array 110 by inputting driving signals to a plurality of row lines. For example, the driving signal may include a transfer control signal for controlling a transfer transistor of each pixel PX, a reset control signal for controlling a reset transistor of each pixel PX, a selection control signal for controlling a selection transistor of each pixel PX, and the like. As an example, the row driver 121 may sequentially drive a plurality of row lines.

The readout circuitry 122 may include sampling circuitry, analog-to-digital converters (ADCs), and so forth. The sampling circuit may include a plurality of samplers connected to the pixels PX through a plurality of column lines, and in an exemplary embodiment of the inventive concept, the samplers may be Correlated Double Samplers (CDS). The sampler may detect a reset voltage and a pixel voltage from the pixels PX connected to a selected row line among the plurality of row lines driven by the row driver 121. The sampler may compare each of the reset voltage and the pixel voltage with the ramp voltage, and may output a comparison result. The analog-to-digital converter may convert the comparison result output from the sampler into a digital signal, and may output the digital signal.

The column driver 123 may include a latch, an amplifier circuit, or the like for temporarily storing a digital signal, and may process the digital signal received from the readout circuit 122. The row driver 121, the read-out circuit 122 and the column driver 123 are controlled by control logic 124. The control logic 124 may include a timing controller for controlling operation timings of the row driver 121, the readout circuit 122, and the column driver 123, an image signal processor for processing image data, and the like. In an exemplary embodiment of the inventive concept, the image signal processor may also be included in an external processor connected to the image sensor 100.

Fig. 2 and 3 are diagrams illustrating an image sensor according to an exemplary embodiment of the inventive concept.

Referring to fig. 2, the image forming apparatus 10 in the present embodiment may include a first layer 11, a second layer 12 disposed under the first layer 11, a third layer 13 disposed under the second layer 12, and the like. In other words, the second layer 12 may be disposed below the first layer 11, and the third layer 13 may be disposed below the second layer 12. The first layer 11, the second layer 12, and the third layer 13 may be stacked in a vertical direction. In exemplary embodiments of the inventive concept, the first layer 11 and the second layer 12 may be laminated at a wafer level, and the third layer 13 may be attached to a lower portion of the second layer 12 at a chip level. The first layer 11 to the third layer 13 may be provided as a single semiconductor package.

The first layer 11 may include a sensing area SA in which a plurality of pixels PX are arranged and a first pad area PA1 arranged around the sensing area SA. The first PAD area PA1 may include a plurality of upper PADs PAD, and the plurality of upper PADs PAD may be connected to PADs arranged in the second PAD area PA2 of the second layer 12 and the control logic LC of the second layer 12 through vias.

Each of the plurality of pixels PX may include a photodiode for receiving light and generating charges, a pixel circuit for processing the charges generated from the photodiode, and the like. The pixel circuit may include a plurality of transistors for outputting a voltage corresponding to the charge generated from the photodiode.

The second layer 12 may comprise a plurality of devices providing control logic LC. A plurality of devices included in the control logic LC may provide circuits for driving the pixel circuits arranged on the first layer 11, such as row drivers, column drivers, timing controllers, and the like. A plurality of devices included in the control logic LC may be connected to the pixel circuit through the first and second pad areas PA1 and PA 2. The control logic LC may obtain a reset voltage and a pixel voltage from a plurality of pixels PX, and may generate a pixel signal.

In an exemplary embodiment of the inventive concept, at least one of the plurality of pixels PX may include a plurality of photodiodes disposed at the same level. The pixel signals generated from the charges of each of the plurality of photodiodes may have a phase difference between the pixel signals. The control logic LC may provide an auto-focusing function based on a phase difference of pixel signals generated from a plurality of photodiodes included in a single pixel PX.

The third layer 13 disposed under the second layer 12 may include a memory chip MC, a dummy chip DC, and a protective layer EN for sealing the memory chip MC and the dummy chip DC. The memory chips may be Dynamic Random Access Memory (DRAM) or Static Random Access Memory (SRAM). The dummy chip DC may not actually store data. The memory chip MC may be electrically connected to at least some devices included in the control logic LC of the second layer 12 through bumps and may store information for providing an auto-focus function. In exemplary embodiments of the inventive concept, the protrusions may be micro-protrusions.

Referring to fig. 3, the image forming apparatus 20 in the present embodiment may include a first layer 21 and a second layer 22. The first layer 21 may include a sensing area SA in which a plurality of pixels PX are arranged, a control logic LC in which devices for driving the plurality of pixels PX are arranged, and a first pad area PA1 arranged around the sensing area SA and the control logic LC. The first PAD area PA1 may include a plurality of upper PADs PAD, and the plurality of upper PADs PAD may be connected to the memory chip MC disposed on the second layer 22 through vias or the like. The second layer 22 may include a memory chip MC, a dummy chip DC, and a protection layer EN for sealing the memory chip MC and the dummy chip DC.

Fig. 4 is a diagram illustrating an operation of an image sensor according to an exemplary embodiment of the inventive concept.

Referring to fig. 4, the pixel array PA of the image sensor in the present embodiment may include a plurality of pixels PX. The plurality of pixels PX may be connected to a plurality of ROW lines ROW1 to ROW (ROW) and a plurality of column lines COL1 to Coln (COL). The image sensor may drive a plurality of pixels PX in units of a plurality of ROW lines ROW. As an example, a time for driving a selected ROW line of the plurality of ROW lines ROW and reading out the reset voltage and the pixel voltage from the pixels PX connected to the selected ROW line may be a single horizontal period. The image sensor may operate in a rolling shutter method of sequentially driving a plurality of ROW lines ROW.

The frame period FT of the image sensor may be each time period for reading out the reset voltage and the pixel voltage from all the pixels included in the pixel array PA. As an example, the frame period FT may be equal to or greater than a product obtained by multiplying the plurality of ROW lines ROW by the horizontal period. The shorter the frame period FT of the image sensor, the greater the number of image frames that the image sensor can generate in the same time period.

Fig. 5 is a circuit diagram illustrating a pixel included in an image sensor according to an exemplary embodiment of the inventive concept.

Referring to fig. 5, the pixels included in the image sensor may include a photodiode PD for generating charges in response to light, a pixel circuit for processing the charges generated from the photodiode PD and outputting an electrical signal, and the like. As an example, the pixel circuit may include a floating diffusion FD, a reset transistor RX, a driving transistor DX, a selection transistor SX, a transfer transistor TX, a switching device SW, and the like.

The reset transistor RX may be connected between a power supply node supplying the power supply voltage VDD and the floating diffusion FD, and controlled by a reset control signal RG. As an example, when the reset transistor RX and the switching device SW are turned on, the voltage of the floating diffusion FD may be reset to the power supply voltage VDD. When the voltage of the floating diffusion FD is reset, the selection transistor SX may be turned on by a selection control signal SEL, and a reset voltage may be output to the column line COL.

In exemplary embodiments of the inventive concept, the photodiode PD may generate electrons or holes as main charge carriers in response to light. When the transfer transistor TX is turned on after the reset voltage is output to the column line COL, the charge generated by the photodiode PD exposed to light may move to the floating diffusion FD. The driving transistor DX may function as a source follower amplifier amplifying a voltage of the floating diffusion FD, and when the selection transistor SX is turned on by the selection control signal SEL, a pixel voltage corresponding to an electric charge generated by the photodiode PD may be output to the column line COL.

Each of the reset voltage and the pixel voltage is detected by a sampling circuit connected to the column line COL. The sampling circuit may include a plurality of samplers having a first input terminal and a second input terminal, and the samplers may receive the ramp voltage through the first input terminal. The sampler may compare the ramp voltage input to the first input terminal with the reset voltage and the pixel voltage input to the second input terminal. An analog-to-digital converter (ADC) may be connected to an output terminal of the sampler, and the ADC may output reset data corresponding to a comparison result between the ramp voltage and the reset voltage. The analog-to-digital converter may also output pixel data corresponding to a result of comparison between the ramp voltage and the pixel voltage. The control logic may generate the image data using a pixel signal corresponding to a difference between the reset data and the pixel data.

The level of the pixel voltage may be determined based on the amount of charge generated by the photodiode PD and moved to the floating diffusion FD, the conversion gain of the pixel circuit, and the like. The conversion gain of the pixel circuit may correspond to a voltage variation of the charge generation and may be inversely proportional to the capacitance of the floating diffusion. Therefore, when the capacitance of the floating diffusion increases, the conversion gain of the pixel circuit may decrease, and when the capacitance of the floating diffusion decreases, the conversion gain of the pixel circuit may increase.

Conversion gain may affect the performance of the image sensor. As an example, when the conversion gain of the pixel circuit is set for a low illumination environment and the pixel voltage generated in the high illumination environment exceeds the dynamic range of the image sensor, the image quality may deteriorate. When the conversion gain of the pixel circuit is set for a high illumination environment, the driving transistor DX may not be sufficiently driven in a low illumination environment, and thus, the image quality may deteriorate.

In order to solve the above-described problems, in an exemplary embodiment of the inventive concept, the conversion gain of the pixel circuit may be dynamically adjusted by turning on or off the switching device SW. For example, whether to turn on or off the switching device SW may be determined in consideration of an exposure time length to which the photodiode PD is exposed, after which a pixel signal may be obtained, and a resultant image may be generated using the pixel signals obtained at different exposure times. Accordingly, noise characteristics, dynamic range, and the like of the image sensor can be improved.

As an example, when the switching device SW is turned off, the capacitance of the floating diffusion FD storing the charge generated from the photodiode PD may be determined as the first capacitance C_FD1. When the switching device SW is turned on, the capacitance of the floating diffusion FD may be determined as the first capacitance C_FD1And a second capacitor C_FD2The sum of (a) and (b). Therefore, by turning off the switching device SW, the capacitance of the floating diffusion FD can be reduced, the conversion gain can be increased, and by turning on the switching device SW, the capacitance of the floating diffusion FD can be increased, and the conversion gain can be reduced. As an example, when the exposure time is relatively long, the switching device SW may be turned off, and when the exposure time is relatively short, the switching device SW may be turned on. For example, a reference time may be set, and the switching device SW may be turned off when the exposure time is longer than the reference time, and may be turned on when the exposure time is shorter than the reference time.

Fig. 6 is a diagram illustrating an operation of adjusting a conversion gain of a pixel in an image sensor according to an exemplary embodiment of the inventive concept.

Images (a) and (b) in fig. 6 are diagrams illustrating the operation of the pixel circuit under the conditions of a relatively high conversion gain and a relatively low conversion gain. In the following description, for convenience of description, example embodiments of the inventive concept will be described with reference to the pixel circuit described in fig. 5.

An image (a) in fig. 6 shows an example in which the switching device SW included in the pixel circuit is turned off. When the switching device SW is turned off, the capacitance of the floating diffusion FD may be determined as the first capacitance C_FD1. An image (b) in fig. 6 shows an example in which the switching device SW is turned on. In this case, the capacitance of the floating diffusion FD may be determined as the first capacitance C_FD1And a second capacitor C_FD2OfAnd (c). Therefore, by turning off the switching device SW, the conversion gain of the pixel circuit can be increased, and by turning on the switching device SW, the conversion gain of the pixel circuit can be decreased.

In order to improve the quality of the resultant image output by the image sensor, the exposure time of the photodiode PD may be set differently, and a plurality of pixel signals may be obtained from the pixel circuit, thereby generating the resultant image. As an example, the exposure time may be extended so that the obtained pixel signal may be applied to an area where light is insufficient, and the pixel signal whose exposure time is shortened may be applied to an area where light is sufficient, thereby improving the quality of the resulting image.

In the present embodiment, the switching device SW may be turned off when the exposure time is extended, and turned on when the exposure time is shortened. Accordingly, the pixel circuit can operate under a condition of a conversion gain suitable for an exposure time, and noise characteristics and a dynamic range of the image sensor can be improved, thereby improving the quality of a resultant image.

Fig. 7 is a diagram illustrating an operation of an image sensor according to an exemplary embodiment of the inventive concept. Fig. 8 and 9 are diagrams illustrating an operation of an image sensor according to an exemplary embodiment of the inventive concept.

The image sensor in the present embodiment may generate an image frame in each of a plurality of frame periods, and may generate a resultant image using the image frame. Referring to fig. 7, the image sensor may drive a plurality of row lines included in the pixel array according to predetermined frame periods FT1 to FT2, and may obtain pixel signals through a plurality of column lines included in the pixel array. For example, F1 and F2 may refer to a first image frame and a second image frame.

The image sensor may control the photodiode of the pixel to be exposed during a first exposure time ET1 in a first frame period FT 1. The image sensor may obtain a first pixel signal corresponding to charges generated from the photodiode during a first frame period FT1, and may generate a first image frame using the first pixel signal. Further, the image sensor may control the photodiode of the pixel to be exposed during a second exposure time ET2 shorter than the first exposure time ET1 in the second frame period FT 2. When the second pixel signal corresponding to the charge generated from the photodiode is generated during the second exposure time ET2, the image sensor may generate a second image frame using the second pixel signal.

In the first image frame corresponding to the first exposure time ET1, a dark area can be displayed relatively clearly compared to the second image frame. In addition, in the first image frame, pixels corresponding to a bright area may be saturated. In the second image frame corresponding to the second exposure time ET2, since the pixels corresponding to the bright area are not saturated, the bright area may be clearly displayed and the dark area may not be clearly displayed. The image sensor may use the first image frame and the second image frame to generate a resultant image that clearly displays both bright and dark regions. For example, the image sensor may generate a result image by selecting a dark region in the first image frame and selecting a bright region in the second image frame. That is, the resulting image may be generated by selecting regions of the first image frame and the second image frame that are clearly displayed.

Further, the image sensor according to an exemplary embodiment of the inventive concept may adjust a conversion gain of each pixel differently when generating the first image frame and generating the second image frame. As an example, the conversion gain of each pixel in the first frame period FT1 may have a first value, and the conversion gain of each pixel in the second frame period FT2 may have a second value smaller than the first value. Further, in an exemplary embodiment of the inventive concept, the first frame period FT1 may be divided into two or more sub-time periods, and the conversion gain of each pixel in each sub-time period may be controlled to have a first value and a second value. In the sub-time period, the first value and the second value may be different from each other. In the following description, exemplary embodiments of the inventive concept will be described with reference to fig. 8 and 9.

The timing charts shown in fig. 8 and 9 may illustrate operations during a horizontal period 1H in which the image sensor drives a single pixel and obtains a pixel signal. As an example, the horizontal period 1H may be a time period in which a controller of the image sensor may drive a selected row line of the plurality of row lines and a pixel signal may be obtained from a column line intersecting the selected row line. In the following description, for convenience of description, an exemplary embodiment of the inventive concept will be described with reference to fig. 5.

Referring to fig. 8, an image (a) is a timing diagram illustrating an operation of the image sensor in the first frame period FT1, and an image (b) is a timing diagram illustrating an operation of the image sensor in the second frame period FT 2. Referring to an image (a), the reset transistor RX is turned on by a reset control signal RG, and the voltage of the floating diffusion FD may be reset. Further, together with the reset transistor RX, the switching device SW is also turned on by the switch control signal SG, and the voltage of the floating diffusion FD can be reset.

When the voltage of the floating diffusion FD is reset, the reset transistor RX and the switching device SW may be turned off, and the correlated double sampler CDS of the readout circuit may read out the first sub-reset voltage V from the pixel_SRT1. When the first sub-reset voltage V is read out_SRT1At this time, the transfer transistor TX is turned on by the transfer control signal TG, and the charge of the photodiode PD can move to the floating diffusion FD.

As an example, when the first sub-reset voltage V is read out_SRT1And the transfer transistor TX is turned on so that the charge of the photodiode PD moves to the floating diffusion FD, the switching device SW may maintain an off state. Accordingly, the capacitance of the floating diffusion FD may be the first capacitance C_FD1The conversion gain of the pixel may be equal to the first capacitance C_FD1A corresponding first value. In other words, the image sensor may move the charge of the photodiode PD to the floating diffusion FD, and may read out the first sub-reset voltage V when the conversion gain has a first value_SRT1. The correlated double sampler CDS may read out the first sub-reset voltage V during the first sub-time period TS1_SRT1And a first sub-pixel voltage V_SPX1And the controller of the image sensor may obtain the first sub-reset voltage V_SRT1And a first sub-pixel voltage V_SPX1The difference therebetween corresponds to the first subpixel signal.

When it comes toWhen the one sub-time period TS1 elapses and the second sub-time period TS2 begins, the image sensor may turn on the switching device SW. In exemplary embodiments of the inventive concept, the turn-on timing of the switching device SW may vary. When the switching device SW is turned on, the capacitance of the floating diffusion FD may be the first capacitance C_FD1And a second capacitor C_FD2Thus, the conversion gain of the pixel may have the same value as the first capacitance C_FD1And a second capacitor C_FD2To a second value corresponding to the sum of. The second value may be less than the first value.

The correlated double sampler CDS may obtain the second sub-pixel voltage V when the conversion gain of the pixel has the second value_SPX2And a second sub-reset voltage V_SRT2. During reading out the second sub-pixel voltage V_SPX2After that, the reset transistor RX may be turned on, and the charge of the floating diffusion FD may be removed, and when the reset transistor RX is turned off, the second sub-reset voltage V may be read out_SRT2. The controller of the image sensor may obtain the second sub-pixel voltage V during the second sub-time period TS2_SPX2And a second sub-reset voltage V_SRT2The difference therebetween corresponds to the second sub-pixel signal. The image sensor may generate a first image frame using the first and second sub-pixel signals obtained in the first frame period FT 1.

Referring to image (b) in fig. 8, the image sensor may control the switching device SW of the pixel to maintain a turn-on state during the second frame period, and may obtain the second reset voltage V from the pixel_RT2And a second pixel voltage V_PX2. The image sensor can use the second reset voltage V_RT2And a second pixel voltage V_PX2The second image frame is generated by the second pixel signal corresponding to the difference between the first and second pixel signals. Further, the image sensor may generate a result image using the first image frame and the second image frame. For example, in images (a) and (b) of fig. 8, the selection control signal SEL may be active during most of the horizontal period 1H.

Referring to fig. 9, an image (a) is a timing chart showing an operation of the image sensor in the first frame period FT1, and an image (b) is a timing chart showing an operation of the image sensor in the first frame period FT1A timing diagram of the operation of the sensor in the second frame period FT 2. Referring to images (a) and (b) of fig. 9, when the correlated double sampler CDS reads out the first reset voltage V in the first frame period FT1_RT1And a first pixel voltage V_PX1When the switching device SW may be turned off (e.g., SG low), and the second reset voltage V is read out when the correlated double sampler CDS is in the second frame period FT2_RT2And a second pixel voltage V_PX2When on, the switching device SW may be on (e.g., SG high). Accordingly, the conversion gain of each pixel may have a relatively large first value during the first frame period FT1 and a relatively small second value during the second frame period FT 2. The image sensor may generate a result image using a first image frame generated in a first frame period FT1 and a second image frame generated in a second frame period FT 2.

The image sensor may expose the photodiode of the pixel during a first exposure time ET1 in the first frame period FT1, and may expose the photodiode of the pixel during a second exposure time ET2 shorter than the first exposure time ET1 in the second frame period FT 2. In this case, the image sensor according to the exemplary embodiments of the inventive concept may increase the conversion gain of the pixels when the exposure time is relatively long, and may decrease the conversion gain of the pixels when the exposure time is relatively short. As described above, by dynamically adjusting the conversion gain of the pixels according to the exposure time, the noise property and the dynamic range can be improved, thereby improving the image quality.

Fig. 10 is a diagram illustrating an operation of an image sensor according to an exemplary embodiment of the inventive concept. Fig. 11 and 12 are diagrams illustrating an operation of an image sensor according to an exemplary embodiment of the inventive concept.

The image sensor in the present embodiment can obtain a plurality of pixel signals from each of a plurality of pixels in a single frame period FT, and can generate a single resultant image using the plurality of pixel signals. Referring to fig. 10, the image sensor may divide a single frame period FT into a first time period T1 and a second time period T2, may drive a plurality of row lines in each of the first time period T1 and the second time period T2, and may obtain pixel signals through a plurality of column lines.

In the embodiment shown in fig. 10, the image sensor may obtain a first pixel signal corresponding to a first time period T1 and a second pixel signal corresponding to a second time period T2. The image sensor may generate a resultant image using the first pixel signal and the second pixel signal. The image sensor may expose the photodiode of the pixel for different exposure times for a first time period T1 and a second time period T2. In an exemplary embodiment of the inventive concept, the time during which the photodiode is exposed to light during the first time period T1 may be longer than the time during which the photodiode is exposed to light during the second time period T2.

The image sensor may adjust the conversion gain of each pixel to have different values in the first time period T1 and the second time period T2. As an example, the image sensor may adjust the conversion gain of each pixel by changing the capacitance of a floating diffusion included in the pixel. In an exemplary embodiment of the inventive concept, the image sensor may adjust the capacitance of the floating diffusion to a first value during a first time period T1 and may adjust the capacitance of the floating diffusion to a second value greater than the first value during a second time period T2, thereby changing a conversion gain of the pixel.

The timing charts shown in fig. 11 and 12 may illustrate operations during a horizontal period 1H in which the image sensor drives a single pixel and obtains a pixel signal. In the following description, for convenience of description, an exemplary embodiment of the inventive concept will be described with reference to a pixel circuit shown in fig. 5.

In the embodiment shown in fig. 11 and 12, the horizontal period 1H may include a first time period T1 and a second time period T2. Further, referring to fig. 11, the first time period T1 may include a first sub-time period TS1 and a second sub-time period TS 2. During the first sub-time period TS1, the reset transistor RX may be turned on by the reset control signal RG and the switching device SW may be turned on by the switch control signal SG such that the voltage of the floating diffusion FD may be reset.

When the voltage of the floating diffusion FD is reset, correlationThe double sampler CDS may read out the first sub-reset voltage V from the pixel_SRT1. When the first sub-reset voltage V is read out_SRT1At this time, the transfer transistor TX may be turned on by the transfer control signal TG so that the charge of the photodiode PD may move to the floating diffusion FD. As an example, when the correlated double sampler CDS reads out the first sub-reset voltage V_SRT1At this time, the transfer transistor TX is turned on, the charge of the photodiode PD moves to the floating diffusion FD, and the switching device SW may maintain an off state. Accordingly, the capacitance of the floating diffusion FD may be the first capacitance C_FD1The conversion gain of the pixel may be equal to the first capacitance C_FD1A corresponding first value. The controller of the image sensor may move charges of the photodiode PD to the floating diffusion FD, and may read out the first sub-pixel voltage V when the conversion gain of the pixel has a first value_SPX1. The controller of the image sensor may obtain the first sub-reset voltage V_SRT1And a first sub-pixel voltage V_SPX1The difference therebetween corresponds to the first subpixel signal.

When the first sub-time period TS1 elapses and the second sub-time period TS2 starts, the image sensor may turn on the switching device SW. In exemplary embodiments of the inventive concept, the turn-on timing of the switching device SW may be moved forward or backward. When the switching device SW is turned on, the capacitance of the floating diffusion FD may be the first capacitance C_FD1And a second capacitor C_FD2And the conversion gain of the pixel may thus have the same value as the first capacitance C_FD1And a second capacitor C_FD2To a second value corresponding to the sum of. The second value may be less than the first value.

The correlated double sampler CDS may sequentially obtain the second sub-pixel voltage V when the conversion gain of the pixel has the second value_SPX2And a second sub-reset voltage V_SRT2. During reading out the second sub-pixel voltage V_SPX2After that, the reset transistor RX may be turned on, and the charge of the floating diffusion FD may be removed, and when the reset transistor RX is turned off, the second sub-reset voltage V may be read out_SRT2. The image sensor may obtain the second sub-reset voltage V during the second sub-time period TS2_SRT2And a second sub-pixel voltage V_SPX2The difference therebetween corresponds to the second sub-pixel signal.

The switching device SW may remain in a turn-on state for a second time period T2 after the first time period T1, and the correlated double sampler CDS may read out the second reset voltage V from the pixel_RT2And a second pixel voltage V_PX2. The controller of the image sensor may calculate the second reset voltage V_RT2And a second pixel voltage V_PX2And a second pixel signal can be obtained. The controller of the image sensor may determine a pixel signal corresponding to each pixel using the first sub-pixel signal, the second sub-pixel signal, and the second pixel signal obtained from each pixel, and may generate a resultant image using the pixel signals. In exemplary embodiments of the inventive concept, a row line to which a pixel outputting a first sub-pixel signal and a second sub-pixel signal through a single column line is connected during a first time period T1 of a single horizontal period 1H may be different from a row line to which a pixel outputting a second pixel signal through a single column line is connected during a second sub-time period TS 2.

Referring to fig. 12, when the correlated double sampler CDS reads out the first reset voltage V in the first time period T1_RT1And a first pixel voltage V_PX1When so, the switching device SW may be turned off (e.g., SG low), and the second reset voltage V is read out when the correlated double sampler CDS is in the second time period T2_RT2And a second pixel voltage V_PX2When on, the switching device SW may be on (e.g., SG high). Accordingly, the conversion gain of the pixel may have a relatively large first value during the first time period T1 and a relatively small second value during the second time period T2. The controller of the image sensor may determine a pixel signal corresponding to each pixel using the first sub-pixel signal, the second sub-pixel signal, and the second pixel signal obtained from each pixel, and may generate a resultant image using the pixel signals. Similar to the embodiment shown in fig. 11, the pixel outputting the first sub-pixel signal and the second sub-pixel signal through the single column line during the first time period T1 of the single horizontal period 1H mayTo be connected to a row line different from the row line connected to the pixel outputting the second pixel signal through the single column line during the second time period T2.

The time during which the photodiode of each pixel is exposed to light in the first time period T1 may be longer than the time during which the photodiode of each pixel is exposed to light in the second time period T2. The controller of the image sensor in the exemplary embodiments of the inventive concept may increase the conversion gain of the pixels when the exposure time is relatively long, and may decrease the conversion gain of the pixels when the exposure time is relatively short. As described above, by dynamically adjusting the conversion gain of the pixels according to the exposure time, the noise characteristics and the dynamic range can be improved, thereby improving the image quality.

Fig. 13 is a diagram illustrating an operation of an image sensor according to an exemplary embodiment of the inventive concept. Fig. 14 and 15 are diagrams illustrating an operation of an image sensor according to an exemplary embodiment of the inventive concept.

In the embodiment shown in fig. 13, the image sensor may generate a single result image using the first, second, and third image frames F1, F2, and F3 obtained during the first, second, and third frame periods FT1, FT2, and FT 3. In the first to third frame periods FT1 to FT3, the pixels may be exposed for exposure times ET1 to ET3 of different time lengths. As an example, the first exposure time ET1 of the first frame period FT1 may be the longest, and the third exposure time ET3 of the third frame period FT3 may be the shortest. The second exposure time ET2 of the second frame period FT2 may be shorter than the first exposure time ET1 and may be longer than the third exposure time ET 3.

Referring to fig. 14 and 15, the operation of the image sensor will be described. Referring to fig. 14, an image (a) is a timing diagram showing an operation of the image sensor in the first frame period FT1, an image (b) is a timing diagram showing an operation of the image sensor in the second frame period FT2, and an image (c) is a timing diagram showing an operation of the image sensor in the third frame period FT 3.

Referring to image (a) in fig. 14, the controller of the image sensor may turn on the reset transistor RX and the switching device SWThe voltage of the floating diffusion FD is reset. When the reset transistor RX is turned off, the correlated double sampler CDS may read out the first sub-reset voltage V from the pixel_SRT1. When the transfer transistor TX is turned on and the charge of the photodiode PD moves to the floating diffusion FD, the correlated double sampler CDS may read out the first sub-pixel voltage V_SPX1. When the correlated double sampler CDS obtains the first sub-reset voltage V in the first sub-time period TS1_SRT1And a first sub-pixel voltage V_SPX1When so, the switching device SW may be turned off (e.g., SG low), and the floating diffusion FD may have a first capacitance C_FD1。

The correlated double sampler CDS may sequentially obtain the second sub-pixel voltage V during a second sub-time period TS2 after the first sub-time period TS1_SPX2And a second sub-reset voltage V_SRT2. The switching device SW may be turned on (e.g., SG high) during the second sub-time period TS2, and the second capacitor C_FD2May be added to the capacitance of the floating diffusion FD. Therefore, the conversion gain of the pixel can be reduced. The controller of the image sensor may use the first sub-reset voltage V_SRT1And a first sub-pixel voltage V_SPX1A first sub-pixel signal corresponding to the difference between the first and second sub-reset voltages_SRT2And a second sub-pixel voltage V_SPX2The second sub-pixel signal corresponding to the difference therebetween generates a first image frame F1 corresponding to the first frame period FT 1.

Referring to images (b) and (c) in fig. 14, the operation of the image sensor in the second frame period FT2 may be similar to the operation of the image sensor in the third frame period FT 3. When the reset transistor RX and the switching device SW are turned on and the voltage of the floating diffusion FD is reset, the correlated double sampler CDS may read out the second reset voltage V_RT2Or a third reset voltage V_RT3. In addition, when the transfer transistor TX is turned on and the charge of the photodiode PD moves to the floating diffusion FD, the correlated double sampler CDS may read out the second pixel voltage V_PX2Or the third pixel voltage V_PX3. The image sensor can use the second reset voltage V_RT2And a second pixel voltage V_PX2Second pixel corresponding to the difference therebetweenThe signal generates a second image frame F2 and a third reset voltage V may be used_RT3And a third pixel voltage V_PX3The third pixel signal corresponding to the difference therebetween generates a third image frame F3.

Fig. 15 includes a timing diagram illustrating an operation of the image sensor in the first to third frame periods FT1 to FT 3. Referring to images (b) and (c) in fig. 15, the operation of the image sensor in the second and third frame periods FT2 and FT3 may be similar to that described with reference to fig. 14.

Referring to image (a) in fig. 15, the correlated double sampler CDS may obtain the first reset voltage V during the first frame period FT1_RT1And a first pixel voltage V_PX1. When the correlated double sampler CDS obtains the first reset voltage V_RT1And a first pixel voltage V_PX1When this occurs, the switching device SW may be turned off (e.g., SG low), and the conversion gain of the pixel may have a relatively large value. The switching device SW may be maintained in an on state (e.g., SG high) during the second and third frame periods FT2 and FT3 shown in images (b) and (c) of fig. 15, and the conversion gain of the pixel may have a relatively small value.

Fig. 16 is a diagram illustrating an operation of an image sensor according to an exemplary embodiment of the inventive concept. Fig. 17 and 18 are diagrams illustrating an operation of an image sensor according to an exemplary embodiment of the inventive concept.

The image sensor in the embodiment shown in fig. 16 may obtain a plurality of pixel signals from each of a plurality of pixels during a single frame period FT, and may generate a single resultant image using the plurality of pixel signals. Referring to fig. 16, the image sensor may divide a single frame period FT into a first time period T1, a second time period T2, and a third time period T3, and may obtain a pixel signal from each of the first time period T1 to the third time period T3. The pixels may be exposed during exposure times of different lengths of time in the first time period T1 through the third time period T3. As an example, the first time period T1 may have the longest exposure time, and the third time period T3 may have the shortest exposure time.

The image sensor may adjust the conversion gain of the pixel to have different values in the first to third time periods T1 to T3. As an example, the image sensor may adjust the conversion gain of the pixel by changing the capacitance of the floating diffusion FD included in the pixel. In an exemplary embodiment of the inventive concept, the image sensor may adjust the capacitance of the floating diffusion FD to a first value during the first time period T1, and may adjust the capacitance of the floating diffusion FD to a second value greater than the first value during the second time period T2 and the third time period T3.

The timing charts shown in fig. 17 and 18 may illustrate operations during the horizontal period 1H in which the image sensor drives a single pixel and obtains a pixel signal. In the following description, for convenience of description, an exemplary embodiment of the inventive concept will be described with reference to a pixel circuit shown in fig. 5.

In the embodiment shown in fig. 17 and 18, the horizontal period 1H may include the first to third time periods T1 to T3. In the embodiment shown in fig. 17, the first time period T1 may include a first sub-time period TS1 and a second sub-time period TS 2. The correlated double sampler CDS may obtain the first sub-pixel voltage V during the first sub-time period TS1_SPX1And a first sub-reset voltage V_SRT1And a second subpixel voltage V may be obtained during a second sub-time period TS2_SPX2And a second sub-reset voltage V_SRT2. In addition, the correlated double sampler CDS may obtain the second reset voltage V during the second time period T2_RT2And a second pixel voltage V_PX2And a third reset voltage V may be obtained during a third time period T3_RT3And a third pixel voltage V_PX3。

Referring to fig. 17, the first sub-reset voltage V is read only when the first sub-reset voltage V is read_SRT1And a first sub-pixel voltage V_SPX1The switching device SW can be turned off. For example, the switch control signal SG transitions to the low level only during the first sub-time period TS 1. Accordingly, the conversion gain of the pixel during the first sub-time period TS1 may be greater than that during the second sub-time period TS2, the second time period T2, and the third time period T3The conversion gain of the pixel during.

Referring to fig. 18, the correlated double sampler CDS may turn off the switching device SW, and may obtain the first reset voltage V during the first time period T1_RT1And a first pixel voltage V_PX1. In addition, the correlated double sampler CDS may obtain the second reset voltage V during the second time period T2_RT2And a second pixel voltage V_PX2And a third reset voltage V may be obtained during a third time period T3_RT3And a third pixel voltage V_PX3. The switching device SW may maintain a conductive state during the second time period T2 and the third time period T3. For example, the switch control signal SG may remain high during the second time period T2 and the third time period T3. Accordingly, when the conversion gain of the corresponding pixel has a relatively large value, the first reset voltage V may be output_RT1And a first pixel voltage V_PX1And the second reset voltage V may be output when the corresponding pixel has a relatively small conversion gain_RT2A second pixel voltage V_PX2A third reset voltage V_RT3And a third pixel voltage V_PX3。

In an exemplary embodiment of the inventive concept, a controller of an image sensor may read out a reset voltage and a pixel voltage from different pixels connected to a single column line in each of first to third time periods T1 to T3 included in a single horizontal period 1H, and may calculate a difference between the reset voltage and the pixel voltage to generate a pixel signal. In the embodiments of fig. 17 and 18, the controller of the image sensor may obtain at least three pixel signals from each pixel. The controller of the image sensor may obtain three pixel signals output from a single pixel in the first time period T1, the second time period T2, and the third time period T3 included in each of the three different horizontal periods 1H.

Fig. 19A and 19B are graphs illustrating an operation of an image sensor according to an exemplary embodiment of the inventive concept.

As an example, fig. 19A may be a graph illustrating an image sensor operating according to the embodiment described with reference to fig. 17. Fig. 19B is a graph illustrating an image sensor operating according to the embodiment described with reference to fig. 18. In the graphs shown in fig. 19A and 19B, the comparative example may correspond to an image sensor in which a pixel may not include a switching device connected between a reset transistor and a floating diffusion.

Fig. 19A and 19B are graphs showing a signal-to-noise ratio (SNR) according to the number of electrons generated in the photodiode and moved to the floating diffusion. In the example shown in fig. 19A, the image sensor may obtain a first sub-pixel signal by turning off the switching device during the first sub-time period TS1, and may obtain a second sub-pixel signal by turning on the switching device during the second sub-time period TS 2. When the switching device is turned off, the conversion gain of the pixel may be increased, and thus, when the number of electrons is reduced, the signal-to-noise ratio may be improved. Accordingly, the noise characteristic and the dynamic range of the image sensor can be improved.

When the exposure time of a pixel is changed, the signal-to-noise ratio according to the number of electrons may be changed. In the embodiment shown in fig. 19A, a second time period T2 may begin after the switching device SW is turned on in the second sub-time period TS 2. Accordingly, the difference in signal-to-noise ratio between the first time period T1 and the second time period T2 may be substantially the same as the difference in signal-to-noise ratio between the second time period T2 and the third time period T3.

In the embodiment shown in fig. 19B, the image sensor may turn off the switching device SW during the first time period T1 and may obtain the first subpixel signal, and may turn on the switching device SW during the second time period T2 and the third time period T3 and may obtain the second subpixel signal. In the embodiment shown in fig. 19B, since the conversion gain of the pixel may be increased during the first time period T1, when the number of electrons is decreased, the signal-to-noise ratio may be increased, so that the noise characteristics and the dynamic range may be improved.

In the embodiment shown in fig. 19B, the maximum signal to noise ratio for the first time period T1 may be less than the maximum signal to noise ratio for the second time period T2. This is because, during the first time period T1, the pixel voltage may not be read out in a state where the switching device of the pixel is turned on and the conversion gain of the pixel is lowered.

Fig. 20 and 21 are diagrams illustrating an operation of an image sensor according to an exemplary embodiment of the inventive concept.

Referring to fig. 20, the pixel array PA of the image sensor may include a plurality of pixels, and four adjacent pixels may form a single pixel group PG. As an example, a single pixel group PG may include a red pixel R, a blue pixel B, and two green pixels GR and GB. Each pixel may have the pixel circuit described with reference to fig. 5.

When a pixel signal is obtained from each pixel, the pixel may be divided into a first pixel PX1 and a second pixel PX 2. As an example, the switching device may be turned off in the first pixel PX1, and the switching device may be turned on in the second pixel PX 2. Accordingly, the conversion gain of the first pixel PX1 may be greater than the conversion gain of the second pixel PX 2.

Fig. 21 may be a graph illustrating an operation of the image sensor having the pixel array PA described with reference to fig. 20. Images (a) and (b) in fig. 21 may be graphs showing the operation of the first pixel PX1, and image (c) in fig. 21 may be a graph showing the operation of the second pixel PX 2.

Referring to image (a) in fig. 21, the correlated double sampler CDS may sequentially read out the first sub-reset voltage V from the first pixel PX1_SRT1A first sub-pixel voltage V_SPX1A second sub-pixel voltage V_SPX2And a second sub-reset voltage V_SRT2. When the first sub-reset voltage V is read out_SRT1And a first sub-pixel voltage V_SPX1When the switching device SW included in the first pixel PX1 may be turned off (e.g., SG low), when the second sub-pixel voltage V is read out_SPX2And a second sub-reset voltage V_SRT2When on, the switching device SW may be on (e.g., SG high).

Referring to image (b) in fig. 21, the correlated double sampler CDS may read out the first reset voltage V from the first pixel PX1_RT1And a first pixel voltage V_PX1. When the correlated double sampler CDS reads out the first reset voltage V_RT1And a first pixel voltage V_PX1At this time, the switching device SW of the first pixel PX1 may be kept turned on, and the capacitance of the floating diffusion FD of the first pixel PX1 may be reduced, and the conversion gain may be increased. Referring to image (c) of fig. 21, when the correlated double sampler CDS reads out the second reset voltage V_RT2And a second pixel voltage V_PX2At this time, the switching device SW of the second pixel PX2 may maintain an on state. Accordingly, the conversion gain of the second pixel PX2 may be smaller than the conversion gain of the first pixel PX 1.

Fig. 22 is a diagram illustrating a pixel array of an image sensor according to an exemplary embodiment of the inventive concept. Fig. 23 is a circuit diagram illustrating a pixel circuit of the image sensor illustrated in fig. 22 according to an exemplary embodiment of the inventive concept.

Referring to fig. 22, the pixel array PA of the image sensor may include a plurality of pixels, and the adjacent first, second, third, and fourth pixels PX1, PX2, PX3, and PX4 may form a single pixel group PG. As an example, photodiodes included in the first to fourth pixels PX1 to PX4 in a single pixel group PG may react to the same color of light and may generate electric charges. In addition, the photodiodes included in a single pixel group PG may share a single column line.

Referring to fig. 23, the first to fourth pixels PX1 to PX4 may include a first photodiode PD1, a second photodiode PD2, a third photodiode PD3 and a fourth photodiode PD4, and a first transfer transistor TX1, a second transfer transistor TX2, a third transfer transistor TX3 and a fourth transfer transistor TX 4. In addition, the first to fourth pixels PX1 to PX4 may share the floating diffusion FD, the reset transistor RX, the driving transistor DX, the selection transistor SX, and the switching device SW. As an example, when one of the first to fourth transmission transistors TX1 to TX4 is turned on, the other transmission transistors may be turned off. The image sensor may sequentially turn on the first to fourth transfer transistors TX1 to TX4, and may obtain a pixel signal corresponding to each of the first to fourth photodiodes PD1 to PD 4. The first, second, third, and fourth transmission control signals TG1, TG2, TG3, and TG4 may be applied to gates of the first to fourth transmission transistors TX1 to TX 4.

The image sensor may apply different exposure times to the first to fourth pixels PX1 to PX 4. As an example, the longest first exposure time may be applied to the first pixel PX1, and the shortest fourth exposure time may be applied to the fourth pixel PX 4. The second exposure time of the second pixel PX2 and the third exposure time of the third pixel PX3 may be shorter than the first exposure time and may be longer than the fourth exposure time. The image sensor may reduce the capacitance of the floating diffusion FD by turning off the switching device SW while reading out the reset voltage and the pixel voltage from the first pixel PX1 to which the longest first exposure time is applied. Further, in an exemplary embodiment of the inventive concept, the switching device SW may be turned off when a reset voltage and a pixel voltage are read out from the second pixel PX2 or from the second pixel PX2 and the third pixel PX 3.

The image sensor may generate a group pixel signal corresponding to a single pixel group PG using pixel signals obtained from the first to fourth pixels PX1 to PX4, and may generate a resultant image using the group pixel signal. Thus, the dynamic range of the resulting image may be improved. In the following description, the operation of the image sensor shown in the embodiment in fig. 22 and 23 will be described in more detail with reference to fig. 24 and 25.

Fig. 24 and 25 are diagrams illustrating an operation of an image sensor according to an exemplary embodiment of the inventive concept.

Referring to fig. 24 and 25, the correlated double sampler CDS may read out a reset voltage and a pixel voltage from each of the first to fourth pixels PX1 to PX4 included in the single pixel group PG. The correlated double sampler CDS may perform a readout operation with respect to the first to fourth pixels PX1 to PX4 during the first to fourth time periods T1 to T4.

Referring to fig. 24, the correlated double sampler CDS may read out the first sub-reset voltage V from the first pixel PX1 during the first time period T1_SRT1A first sub-pixel voltage V_SPX1A second sub-pixel voltage V_SPX2And a second sub-reset voltage V_SRT2. When the correlated double sampler CDS reads out the first sub-reset voltage V_SRT1And a first sub-pixel voltage V_SPX1When this occurs, the switching device SW may be turned off. In addition, when the correlated double sampler CDS reads out the second sub-pixel voltage V_SPX2And a second sub-reset voltage V_SRT2When this occurs, the switching device SW may be turned on. Accordingly, during a portion of the first time period T1, the capacitance of the floating diffusion FD may be limited to the first capacitance C_FD1。

The switching device SW may maintain a conductive state during the second to fourth time periods T2 to T4. Accordingly, when the readout operation is performed in association with the second to fourth time periods T2 to T4, the capacitance of the floating diffusion FD may be the first capacitance C_FD1And a second capacitor C_FD2The sum of (a) and (b). Accordingly, the conversion gain of the pixel group PG may be reduced during the second time period T2 to the fourth time period T4.

Referring to fig. 25, the correlated double sampler CDS may read out the first reset voltage V from the first pixel PX1 during the first time period T1_RT1And a first pixel voltage V_PX1. When the correlated double sampler CDS reads out the first reset voltage V_RT1And a first pixel voltage V_PX1When this occurs, the switching device SW may be turned off. Therefore, the capacitance of the floating diffusion FD in the first time period T1 can be limited to the first capacitance C_FD1And the conversion gain of the pixel group PG may be increased.

Similar to the embodiment shown in fig. 24, the switching device SW may maintain a conductive state during the second to fourth time periods T2 to T4. Accordingly, when the readout operation is performed in association with the second to fourth time periods T2 to T4, the capacitance of the floating diffusion FD may be the first capacitance C_FD1And a second capacitor C_FD2The sum of (a) and (b). Accordingly, the conversion gain of the pixel group PG may be reduced during the second time period T2 through the fourth time period T4.

The controller of the image sensor may calculate a difference between the reset voltage and the pixel voltage obtained in each of the first to fourth time periods T1 to T4, may obtain a pixel signal related to the pixel group PG, and may generate a resultant image using the pixel signal. In the readout operation related to at least one or more of the first time period T1 through the fourth time period T4 included in the single pixel group PG, the dynamic range of the image sensor may be improved by increasing the conversion gain of the corresponding pixel.

Fig. 26 is a block diagram illustrating an electronic device including an image sensor according to an exemplary embodiment of the inventive concept.

The computer device 1000 in the embodiment shown in fig. 26 may include a display 1010, a sensor portion 1020, a memory 1030, a processor 1040, a port 1050, and other components. The computer device 1000 may also include wired and/or wireless communication devices, power supply devices, and the like. Among the elements shown in fig. 26, a port 1050 may be provided for computer device 1000 to communicate with video cards, sound cards, memory cards, Universal Serial Bus (USB) devices, and the like. In addition to a desktop or laptop computer, the computer device 1000 may be a smartphone, tablet Personal Computer (PC), smart wearable device, or the like.

Processor 1040 may process specific calculations or commands or may perform tasks. The processor 1040 may be a Central Processing Unit (CPU), a microprocessor unit (MCU), a system on a chip (SoC), etc., and may communicate with the display 1010, the sensor section 1020, and the memory 1030, and may also communicate with other devices connected to the port 1050.

The memory 1030 may be a storage medium storing data or multimedia data, etc. for the operation of the computer device 1000. Memory 1030 may include volatile memory, such as Random Access Memory (RAM), or may include non-volatile memory, such as flash memory or the like. In addition, the memory 1030 may include a Solid State Drive (SSD), a Hard Disk Drive (HDD), or an optical drive (ODD) as a storage device. Input and output devices may also be included in computer device 1000 or connected to computer device 100, and may include input devices such as a keyboard, mouse, touch screen, and output devices such as a display, audio output unit, etc., provided to a user.

The sensor section 1020 may include various sensors such as an image sensor, a gyro sensor, a GPS sensor, an illumination sensor, and the like. According to the exemplary embodiments described with reference to fig. 1 to 25, the image sensor included in the sensor portion 1020 may be used in the computer apparatus 1000.

According to the foregoing exemplary embodiments of the present inventive concept, a resultant image may be generated using pixel signals obtained when conversion gains of pixels have different values. Accordingly, different conversion gains may be applied to a dark region and a bright region of an object to be imaged, thereby improving noise characteristics and a dynamic range of the image sensor.

While the inventive concept has been shown and described with reference to exemplary embodiments thereof, it will be apparent to those skilled in the art that modifications and variations can be made to the inventive concept without departing from the scope of the inventive concept as set forth in the appended claims.