阅读说明：本技术 源极驱动器
(Source driver
) 是由 周志宪
程智修
林晋毅 于 2019-07-16 设计创作，主要内容包括：一种源极驱动器,用以驱动有机发光二极管(OLED)显示面板。所述源极驱动器包括感测电路以及运算放大器。感测电路经配置为经由OLED显示面板的感测线去感测OLED像素电路的像素信息。运算放大器包括放大器电路以及至少一个开关电路。放大器电路包括至少一个增益电路。放大器电路的输入端耦接至感测电路的输出端。所述至少一个开关电路的每一个耦接于所述至少一个增益电路中的一相应者的输出端对之间。(A source driver is used for driving an Organic Light Emitting Diode (OLED) display panel. The source driver includes a sensing circuit and an operational amplifier. The sensing circuit is configured to sense pixel information of the OLED pixel circuit via a sensing line of the OLED display panel. The operational amplifier includes an amplifier circuit and at least one switching circuit. The amplifier circuit includes at least one gain circuit. An input of the amplifier circuit is coupled to an output of the sensing circuit. Each of the at least one switching circuit is coupled between a pair of outputs of a corresponding one of the at least one gain circuit.)
1. A source driver for driving an organic light emitting diode display panel, the source driver comprising:
a sensing circuit configured to sense pixel information of an organic light emitting diode pixel circuit via a sensing line of the organic light emitting diode display panel; and
an operational amplifier, wherein the operational amplifier comprises:
an amplifier circuit comprising at least one gain circuit, wherein an input of the amplifier circuit is coupled to an output of the sensing circuit; and
at least one switching circuit, each of the at least one switching circuit coupled between a pair of output terminals of a respective one of the at least one gain circuit.
2. The source driver of claim 1, wherein each of the at least one switching circuit is configured to pull the output pair of the respective gain circuit to the output voltage pair output to a particular voltage during a reset phase.
3. The source driver of claim 2, wherein the particular voltage is at a level between original levels of the pair of output terminals of the respective gain circuit.
4. The source driver of claim 1, wherein one of the at least one switching circuit is coupled between a pair of output terminals of an output stage of the amplifier circuit.
5. The source driver of claim 1, wherein the operational amplifier further comprises an additional gain circuit having an output terminal pair, wherein the output terminal pair of the additional gain circuit is coupled to a coupled terminal pair of an input stage of the amplifier circuit.
6. The source driver of claim 1, wherein the switch circuit is configured to affect the output pair of the respective one of the at least one gain circuit to the output voltage pair during a first period of a reset phase, and to cease affecting the output voltage pair during a second period of the reset phase.
7. The source driver of claim 1, wherein the switch circuit is configured to affect the output pair of the respective one of the at least one gain circuit to the output voltage pair output during a reset phase, and to stop affecting the output voltage pair during an amplification phase.
8. The source driver of claim 1, wherein each of the switch circuits comprises a switch coupled between the pair of output terminals of the respective one of the at least one gain circuit.
9. The source driver of claim 1, further comprising:
an offset voltage storage and reduction circuit coupled to at least two of the at least one gain circuit.
10. The source driver of claim 9, wherein an output of the offset voltage storage and reduction circuit is coupled to a coupled terminal of a first gain circuit of the at least one gain circuit of the amplifier circuit, and an input of the offset voltage storage and reduction circuit is coupled to an output of a second gain circuit of the at least one gain circuit of the amplifier circuit.
11. The source driver of claim 9, wherein the offset voltage storage and reduction circuit is configured to store and reduce an offset voltage of a first gain circuit of the at least two gain circuits of the amplifier circuit.
12. The source driver of claim 9, wherein the offset voltage storage and reduction circuit comprises:
a pair of sampling switches, each of the pair of sampling switches having a first end coupled to the output of a second gain circuit of the at least two gain circuits of the amplifier circuit;
a pair of sampling capacitors, each of the pair of sampling capacitors coupled to a second end of a respective switch of the pair of sampling switches; and
a transconductance circuit having an input terminal pair coupled to the second terminal of the pair of sampling switches, wherein each of the output terminal pair of the transconductance circuit of the offset voltage storage and reduction circuit is coupled to the coupled terminal of a first gain circuit of the at least two gain circuits of the amplifier circuit.
13. The source driver of claim 12, wherein one of the at least one switching circuit comprises a switch coupled between the pair of output terminals of the second gain circuit and to the pair of sampling switches.
14. The source driver of claim 12, wherein one of the at least one switching circuit comprises a switch coupled between the pair of sampling capacitors and the pair of input terminals of the transconductance circuit of the offset voltage storage and reduction circuit.
15. The source driver of claim 12, wherein one of the at least one switching circuit comprises a pair of switches, one of the pair of switches coupled between one of the pair of inputs of the transconductance circuit of the offset voltage storage and reduction circuit and a reference voltage.
Technical Field
The present invention relates to a display device, and more particularly, to a source driver for driving an organic light-emitting diode (OLED) display panel.
Background
In the OLED display device, since a Thin Film Transistor (TFT) or an Organic Light Emitting Diode (OLED) in a pixel circuit deteriorates with time, a source driver needs to detect and compensate the pixel circuit. Generally, an operational amplifier in the source driver senses pixel information of the OLED pixel circuit through a sensing line of the OLED display panel, and then transmits the pixel information to an analog-to-digital converter (ADC). An analog-to-digital converter converts this pixel information into digital data. This digital data is passed back to the system on chip (SoC). The system chip calculates the compensated driving voltage value according to the digital data and transmits the compensated driving voltage value back to the source driver, so that compensation is realized.
In the source driver, the operational amplifier generally has an offset error (offset error), which greatly affects the performance of the whole system. Therefore, how to perform offset cancellation (offset cancellation) on the operational amplifier is one of the technical issues in the art. In particular, defects in one (or some) pixel (pixel) circuit often affect the offset cancellation (offset cancellation) operation, resulting in errors in the value (pixel information) sensed by the next pixel circuit.
It should be noted that the background section is provided to aid in understanding the invention. Some (or all) of the disclosure in the "background" section may not be prior art as would be known to one of ordinary skill in the art. The disclosure in the "background" section is not intended to represent a limitation on the disclosure that would have been known to one of ordinary skill in the art prior to the filing date of the present application.
Disclosure of Invention
The present invention provides a source driver which can reduce the influence of the pixel information of the previous pixel circuit on the pixel information of the current pixel circuit.
An embodiment of the invention provides a source driver for driving an organic light-emitting diode (OLED) display panel. The source driver includes a sensing circuit and an operational amplifier. The sensing circuit is configured to sense pixel information of the OLED pixel circuit via a sensing line of the OLED display panel. The operational amplifier includes an amplifier circuit and at least one switching circuit. The amplifier circuit includes at least one gain circuit. An input of the amplifier circuit is coupled to an output of the sensing circuit. Each of the at least one switching circuit is coupled between a pair of outputs of a corresponding one of the at least one gain circuit.
Based on the above, the source driver according to the embodiments of the present invention has the switch circuit. The switch circuit is coupled to an output terminal pair of one gain circuit of the amplifying circuit. During the reset phase, the switching circuit may influence (e.g. reset) the output voltage of the pair of output terminals. Therefore, the source driver can reduce the influence of the pixel information of the previous pixel circuit on the pixel information of the current pixel circuit.
In order to make the aforementioned and other features and advantages of the invention more comprehensible, embodiments accompanied with figures are described in detail below.
Drawings
Fig. 1 is a schematic block diagram of a source driver according to an embodiment of the invention.
FIG. 2 is a block diagram illustrating the sensing circuit and the amplifier circuit of FIG. 1 according to an embodiment of the invention.
Fig. 3 is a circuit block diagram illustrating the switching circuit shown in fig. 1 and the amplifier shown in fig. 2 according to an embodiment of the invention.
Fig. 4 is a circuit block diagram illustrating the amplifier of fig. 2 according to another embodiment of the invention.
FIG. 5 is a block diagram illustrating an offset voltage storage and reduction circuit according to another embodiment of the present invention.
Fig. 6 is a circuit block diagram illustrating a switching circuit according to another embodiment of the invention.
Fig. 7 is a circuit block diagram illustrating a switching circuit according to yet another embodiment of the invention.
Description of the symbols
10: organic Light Emitting Diode (OLED) display panel
11: sensing line
100: source driver
110: sensing circuit
120: operational amplifier
121: amplifier circuit
122: switching circuit
123: offset voltage storage and reduction circuit
130: analog-to-digital converter (ADC)
410. 430: mutual conductance circuit
420: load circuit
AMP: amplifier with a high-frequency amplifier
C1, C2, C5, C6: sampling capacitor
C3, C4: capacitor with a capacitor element
CPAR: parasitic capacitance
G1, G2: gain circuit
R1, R2: resistance circuit
SW1, SW2, SW11, SW 12: sampling switch
SW3, SW 4: switching circuit
SW5, SW6, SW7, SW8, SW9, SW10, SW31, SW61, SW71, SW 72: switch with a switch body
VA, VB, Vref: reference voltage
Vout: output of
Vref 2: reference voltage
Detailed Description
The term "coupled" as used throughout this specification, including the claims, may refer to any direct or indirect connection. For example, if a first device couples (or connects) to a second device, it should be construed that the first device may be directly connected to the second device or the first device may be indirectly connected to the second device through other devices or some means of connection. The terms "first," "second," and the like, as used throughout this specification, including the claims, are used to designate elements (elements) or to distinguish between different embodiments or ranges, and are not used to limit the number of elements, nor the order of the elements. Further, wherever possible, the same reference numbers will be used throughout the drawings and the description to refer to the same or like parts. Elements/components/steps in different embodiments using the same reference numerals or using the same terms may be referred to one another in relation to the description.
Fig. 1 is a schematic circuit block diagram of a source driver 100 according to an embodiment of the invention. The source driver 100 may be used to drive an organic light-emitting diode (OLED) display panel 10. The present embodiment does not limit the driving details of the OLED display panel 10 by the source driver 100. For example, the source driver 100 may be configured with a conventional source driving circuit or other driving circuits to drive a plurality of source lines (data lines) of the OLED display panel 10 according to design requirements.
In the embodiment shown in fig. 1, the source driver 100 includes a sensing circuit 110, an operational amplifier 120, and an analog-to-digital converter (ADC) 130. The sensing circuit 110 can sense pixel information of an OLED pixel circuit (not shown) in the OLED display panel 10 through the sensing line 11 of the OLED display panel 10. The present embodiment does not limit the implementation details of the OLED pixel circuit. The OLED pixel circuit can be a conventional pixel circuit or other pixel circuits, for example, according to design requirements.
The operational amplifier 120 is coupled to the sensing circuit 110 to receive the pixel information. That is, the operational amplifier 120 can sense pixel information of the OLED pixel circuit (not shown) through the sensing line 11 of the OLED display panel 10, and then the operational amplifier 120 transmits the pixel information to the analog-to-digital converter 130. The analog-to-digital converter 130 converts this pixel information into digital data. The digital data may be processed to generate a compensated driving voltage value according to the digital data, and the compensated driving voltage value may be transmitted back to the source driver 100, so as to achieve compensation.
In the embodiment shown in fig. 1, the operational amplifier 120 includes an amplifier circuit 121 and a switch circuit 122. An input of the amplifier circuit 121 is coupled to an output of the sensing circuit 110 to receive the pixel information. The amplifier circuit 121 includes at least one gain circuit. For example, in some embodiments, the amplifier circuit 121 includes a plurality of gain circuits (including a first gain circuit and a second gain circuit connected in series with each other). Preferably, but not limitatively, the first gain circuit may serve as an input stage of the amplifier circuit 121, and the second gain circuit may serve as an output stage of the amplifier circuit 121. In other embodiments, the amplifier circuit 121 includes a first gain circuit, at least one second gain circuit, and a third gain circuit connected in series with each other, wherein the first gain circuit may serve as an input stage of the amplifier circuit 121, each of the at least one second gain circuit may serve as an intermediate stage (or gain stage) of the amplifier circuit 121, and the third gain circuit serves as an output stage of the amplifier circuit 121.
The switch circuit 122 is coupled between a pair of output terminals of a corresponding one of the gain circuits of the amplifying circuit 121. In other embodiments, a plurality of switching circuits may be provided, each of which may be coupled to a pair of output terminals of a respective one of the gain circuits. During the reset phase, the switching circuit 122 may affect (e.g., reset) the output voltage of the pair of output terminals. For example, but not limited to, during a reset phase, the switch circuit 122 may pull the output terminal of the corresponding gain circuit to a specific voltage (receive voltage). The level of the specific voltage may be determined according to design requirements. The specific voltage may be a level between original levels of a pair of output terminals of the corresponding gain circuit.
In some embodiments, the switch circuit 122 may be turned on during a first period of the reset phase to affect the output voltage pair output by the output terminal of the corresponding gain circuit, and turned off during a second period of the reset phase to stop affecting the output voltage pair. In some or other embodiments, the switch circuit 122 may be turned on during a reset phase (for at least some time of the reset phase) to affect the output voltage pair output by the output terminal of the corresponding gain circuit, and turned off during an amplification phase (amplification phase) to stop affecting the output voltage pair. Therefore, the source driver can reduce the influence of the pixel information of the previous pixel circuit on the pixel information of the current pixel circuit.
For example, in some embodiments, the switching circuit 122 includes a switch. The switches are coupled between the pair of output terminals of the corresponding gain circuit of the amplification circuit 121. As an example, a switching circuit is provided coupled between a pair of output terminals of an output stage of the amplifier circuit. As another example, a plurality of switching circuits are arranged, each switching circuit being coupled between a pair of outputs of one gain circuit of the at least one gain circuit of the amplifier circuit.
Fig. 2 is a circuit block diagram illustrating the sensing circuit 110 and the amplifier circuit 121 shown in fig. 1 according to an embodiment of the invention. In the embodiment shown in fig. 2, the sensing circuit 110 includes a sampling switch SW1, a sampling switch SW2, a sampling capacitor C1, a sampling capacitor C2, a switching circuit SW3 and a switching circuit SW 4. The first terminal of the sampling switch SW1 is coupled to the sensing line 11 of the OLED display panel 10, and the first terminal of the sampling switch SW2 is coupled to the reference voltage Vref. The level of the reference voltage Vref may be determined according to design requirements. For example, the reference voltage Vref may be a Common mode voltage (Common mode voltage), a ground voltage, or other reference voltages. During the sampling period (sensing period), the sampling switch SW1 and the sampling switch SW2 are turned on (turn on). During the non-sampling period, the sampling switch SW1 and the sampling switch SW2 are turned off (turn off).
The first terminal of the sampling capacitor C1 is coupled to the second terminal of the sampling switch SW 1. The second terminal of the sampling capacitor C1 is coupled to the reference voltage Vref. The first terminal of the sampling capacitor C2 is coupled to the second terminal of the sampling switch SW 2. The second terminal of the sampling capacitor C2 is coupled to the reference voltage Vref. The first terminal of the switching circuit SW3 is coupled to the first terminal of the sampling capacitor C1. The first terminal of the switching circuit SW4 is coupled to the first terminal of the sampling capacitor C2. The second terminals of the switching circuit SW3 and the switching circuit SW4 are used as the output terminals of the sensing circuit 110. When the sensing line 11 is selected as the current sensing line, the switching circuit SW3 and the switching circuit SW4 are turned off in the reset phase. When the sensing line 11 is selected as the current sensing line, the switching circuit SW3 and the switching circuit SW4 are turned on during the amplifying stage. When the sensing line 11 is not the current sensing line, the switching circuit SW3 and the switching circuit SW4 are turned off.
In the embodiment shown in fig. 2, the amplifier circuit 121 includes a switch SW5, a switch SW6, a switch SW7, a switch SW8, a switch SW9, a switch SW10, a capacitor C3, a capacitor C4, and an amplifier AMP. The capacitor CPAR shown in fig. 2 represents a parasitic capacitance (parasitic capacitance).
A first terminal of the capacitor C3 is coupled to a first input terminal of the amplifier AMP of the operational amplifier 120. A first terminal of the capacitor C4 is coupled to a second input terminal of the amplifier AMP of the operational amplifier 120. A first terminal of the switch SW5 is coupled to a first terminal of the capacitor C3. A first terminal of the switch SW6 is coupled to a first terminal of the capacitor C4. The second terminals of the switches SW5 and SW6 are coupled to the reference voltage Vref. The level of the reference voltage Vref may be determined according to design requirements. For example, the reference voltage Vref may be a common mode voltage, a ground voltage, or other reference voltages.
A first terminal of the switch SW9 is coupled to a second terminal of the capacitor C3. A first terminal of the switch SW10 is coupled to a second terminal of the capacitor C4. Second terminals of the switches SW9 and SW10 are respectively coupled to the first output terminal and the second output terminal of the amplifier AMP of the operational amplifier 120. The first output terminal and the second output terminal of the amplifier AMP are coupled to the analog-to-digital converter 130. A first terminal of the switch SW7 is coupled to a second terminal of the capacitor C3. The second terminal of the switch SW7 is coupled to the reference voltage VA. A first terminal of the switch SW8 is coupled to a second terminal of the capacitor C4. A second terminal of the switch SW8 is coupled to the reference voltage VB.
The levels of the reference voltages VA and VB can be determined according to design requirements. For example, the reference voltages VA and VB may be the same voltage level. Alternatively, the amplifier circuit 121 may use different reference voltages VA and VB to generate an offset voltage level at the output terminal of the amplifier AMP.
During the sampling period (sensing period), the pixel information of the sensing line 11 and the reference voltage Vref are stored in the sampling capacitances C1 and C2, respectively. In the reset phase, the switches SW9 and SW10 are turned off, and the switches SW5, SW6, SW7 and SW8 are turned on, so that the capacitors C3 and C4 store the reference voltage VA and the reference voltage VB, respectively.
During the amplification stage, the switches SW9 and SW10 are turned on, and the switches SW5, SW6, SW7 and SW8 are turned off. When the sensing line 11 is selected as the current sensing line, the pixel information stored in the sampling capacitors C1 and C2 is transmitted to the input terminal of the amplifier AMP during the amplification stage. In an ideal case (without any parasitic capacitance and offset voltage), the amplifier AMP amplifies the pixel information by a factor of C3/C1 (or C4/C2) to generate an output signal to the analog-to-digital converter 130.
Fig. 3 is a block diagram illustrating the switching circuit 122 shown in fig. 1 and the amplifier AMP shown in fig. 2 according to an embodiment of the invention. In the embodiment shown in fig. 3, the amplifier AMP includes a gain circuit G1 and a gain circuit G2. The gain circuit G1 may include an input stage of the amplifier circuit 121, and the gain circuit G2 may include an output stage of the amplifier circuit 121. An input terminal of the gain circuit G1 serves as an input terminal of the amplifier AMP to be coupled to the sensing circuit 110. An output terminal of the gain circuit G1 serves as an output terminal of the amplifier AMP to be coupled to the analog-to-digital converter 130. The implementation of the gain circuits G1 and G2 is not limited in this embodiment. For example, the gain circuit G1 and/or the gain circuit G2 may be conventional gain circuits in conventional operational amplifiers, or the gain circuit G1 and/or the gain circuit G2 may be other gain circuits, depending on design requirements.
In the embodiment shown in fig. 3, the switch circuit 122 includes a switch SW 31. A first terminal of switch SW31 is coupled to a first terminal of the pair of output terminals of gain circuit G1. A second terminal of the switch SW31 is coupled to a second terminal of the pair of output terminals of the gain circuit G1. At least some time during the reset phase, switch SW31 is conductive, so that the switch circuit 122 can short circuit the pair of outputs of gain circuit G1, thus pulling the pair of outputs of gain circuit G1 to the particular voltage. During the amplification stage, the switch SW31 is turned off, so the switch circuit 122 can stop affecting the output voltage pair outputted by the output terminal of the gain circuit G1.
Fig. 4 is a circuit block diagram illustrating the amplifier AMP of fig. 2 according to another embodiment of the invention. In the embodiment shown in fig. 4, the amplifier AMP includes a gain circuit G1 and a gain circuit G2. The gain circuit G1, the gain circuit G2 and the switch circuit 122 shown in fig. 4 can be referred to the related description of fig. 3, and therefore, the description thereof is omitted.
In the embodiment shown in fig. 4, the source driver further includes an offset voltage storage and reduction circuit 123. The output terminal of the offset voltage storage and reduction circuit 123 is coupled to the coupling terminal of the gain circuit G1 of the amplifier circuit 121. The input terminal of the offset voltage storage and reduction circuit 123 is coupled to the output terminal of the gain circuit G1 of the amplifier circuit 121. The offset voltage storing and reducing circuit 123 may be configured to store and reduce the offset voltage of the gain circuit G1 of the amplifier circuit 121. For example, during the reset phase, the offset voltage storage and reduction circuit 123 may store a first voltage received from the output terminal of the gain circuit G1, wherein the first voltage carries information about the offset voltage of the gain circuit G1 of the amplifier circuit 121. During the amplification stage, the offset voltage storage and reduction circuit 123 may output a second voltage to the coupled terminal of the gain circuit G1 of the amplifier circuit 121, wherein the second voltage carries information for reducing the offset voltage of the gain circuit G1 of the amplifier circuit 121.
In the embodiment shown in fig. 4, the gain circuit G1 includes a transconductance circuit 410 and a load circuit 420. An input of transconductance circuit 410 is coupled to sensing circuit 110. The load circuit 420 is coupled to the output of the transconductance circuit 410 in the gain circuit G1. The output of transconductance circuit 410 may be coupled to gain circuit G1. The output terminal of the load circuit 420 is coupled to the analog-to-digital converter 130. The implementation of the transconductance circuit 410 and the load circuit 420 is not limited in this embodiment. Transconductance circuit 410 may be a conventional transconductance circuit or other transconductance circuit, depending on design requirements. The load circuit 420 may be a conventional load circuit in a conventional gain circuit, or the load circuit 420 may be another load circuit, according to design requirements. For example, the input pair may serve as the transconductance circuit 410 of the gain circuit G1 of the amplifier circuit 121, and the gain stage may serve as the load circuit 420 of the gain circuit G1 of the amplifier circuit 121. The output terminal of the offset voltage storage and reduction circuit 123 is coupled to the output terminal of the transconductance circuit 410 (the coupling terminal of the gain circuit G1). The input terminal of the offset voltage storage and reduction circuit 123 is coupled to the output terminal of the gain circuit G1. The offset voltage storage and reduction circuit 123 may store and reduce the offset voltage of the gain circuit G1.
In the embodiment shown in fig. 4, the offset voltage storage and reduction circuit 123 may include an additional gain circuit (additional gain circuit) coupled to the gain circuits G1 and G2. More specifically, the offset voltage storage and reduction circuit 123 may include a pair of sampling switches (SW11 and SW12), a pair of sampling capacitors (C5 and C6), and a transconductance circuit 430. The first terminals (the input terminals of the offset voltage storing and reducing circuit 123) of the sampling switch SW11 and the sampling switch SW12 are respectively coupled to the two output terminals of the gain circuit G1. In the embodiment shown in FIG. 4, switch SW31 is also coupled to the first terminals of the pair of sampling switches SW11 and SW 12. The first terminal of the sampling capacitor C5 is directly coupled to the second terminal of the sampling switch SW 11. The first terminal of the sampling capacitor C6 is directly coupled to the second terminal of the sampling switch SW 12. The second terminals of the sampling capacitor C5 and the sampling capacitor C6 are coupled to the reference voltage Vref. The level of the reference voltage Vref may be determined according to design requirements. For example, the reference voltage Vref may be a common mode voltage, a ground voltage, or other reference voltages. The input terminal of the transconductance circuit 430 is coupled to the second terminals of the sampling switch SW11 and the sampling switch SW 12. The output terminal of transconductance circuit 430 (the output terminal of offset voltage storage and reduction circuit 123) is coupled to the output terminal of transconductance circuit 410 (the coupled terminal of gain circuit G1). The present embodiment does not limit the implementation of transconductance circuit 430. For example, transconductance circuit 430 may be a conventional transconductance circuit or other transconductance circuit, depending on design requirements.
It is assumed that the offset voltage of transconductance circuit 410 (the offset voltage of gain circuit G1) is Vos1 and the offset voltage of transconductance circuit 430 is Vos 2. Please refer to fig. 2 and fig. 4. In the reset phase, the switch SW5, the switch SW6, the sampling switch SW11 and the sampling switch SW12 are turned on, and the switching circuit SW3 and the switching circuit SW4 are turned off. At this time, the output Vout of the amplifier AMP is-Vos 1 × Gm1/Gm2-Vos2, where Gm1 represents the transconductance value of the transconductance circuit 410 and Gm2 represents the transconductance value of the transconductance circuit 430. The output Vout is stored in the sampling capacitor C5 and the sampling capacitor C6 during the reset phase.
In the amplifying stage, the switch SW5, the switch SW6, the sampling switch SW11 and the sampling switch SW12 are turned off, and the switching circuit SW3 and the switching circuit SW4 are turned on. At this time, the offset voltage is Vos' ═ Vos1/(Gm2 × R) + Vos2/(Gm1 × R), where R denotes the resistance value of the load circuit 420. The input offset voltage Vos1 of the transconductance circuit 410 is divided by the open-loop gain (open-loop) Gm 2R, and the input offset voltage Vos2 of the transconductance circuit 430 is divided by the open-loop gain Gm 1R, so that the offset voltage of the amplifier circuit 121 can be effectively reduced. In practical designs, the open loop gain is usually large enough, so the offset voltages Vos1 and Vos2 can be ignored, and the input reference offset (inputtreferered offset) can be eliminated.
It should be noted that, since the sampling switch SW11 and the sampling switch SW12 are turned off during the amplifying stage, the offset voltage storing and reducing circuit 123 does not cause a loading effect on the amplifier circuit 121. Furthermore, since the sampling capacitor C5 and the sampling capacitor C6 are not in the signal path, the capacitance design of the amplifier circuit 121 is not affected by the sampling capacitor C5 and the sampling capacitor C6, i.e., the capacitance (area) of the sampling capacitor C5 and the capacitance (area) of the sampling capacitor C6 can be as small as possible.
Fig. 5 is a block diagram illustrating an offset voltage storage and reduction circuit 123 according to another embodiment of the present invention. In the embodiment shown in fig. 5, the offset voltage storing and reducing circuit 123 includes a sampling switch SW11, a sampling switch SW12, a resistor circuit R1, a resistor circuit R2, a sampling capacitor C5, a sampling capacitor C6, and a transconductance circuit 330. The offset voltage storage and reduction circuit 123, the sampling switch SW11, the sampling switch SW12, the sampling capacitor C5, the sampling capacitor C6 and the transconductance circuit 330 shown in fig. 5 can refer to the related description of fig. 4, and thus are not described again.
In the embodiment shown in FIG. 5, the first terminal of the resistor circuit R1 is coupled to the second terminal of the sampling switch SW 11. The second terminal of the resistor circuit R1 is coupled to the first terminal of the sampling capacitor C5. The first terminal of the resistor circuit R2 is coupled to the second terminal of the sampling switch SW 12. The second terminal of the resistor circuit R2 is coupled to the first terminal of the sampling capacitor C6. The phase margin (phase margin) of the auxiliary loop can be improved by using additional resistor circuits R1 and R2. The resistor circuits R1 and R2 may be polysilicon/diffusion resistors(poly/diffusion resistor), a transistor, or any device with a finite resistance. The additional resistors R1 and R2 create a zero point (create a zero) that compensates for the second pole (2)ndpole) to increase the phase margin so that the design of the compromise between the main signal loop and the auxiliary loop can be relaxed.
Fig. 6 is a circuit block diagram illustrating the switching circuit 122 according to another embodiment of the invention. The sensing circuit 110, the analog-to-digital converter (ADC)130, the amplifier AMP, and/or the offset voltage storage and reduction circuit 123 shown in fig. 6 can be described with reference to fig. 4 or fig. 5, and therefore are not repeated herein.
In the embodiment shown in FIG. 6, switch circuit 122 includes switch SW 61. The first terminal of the switch SW61 is coupled to the first terminal of the sampling capacitor C5 and the second terminal of the sampling switch SW 11. The second terminal of the switch SW61 is coupled to the first terminal of the sampling capacitor C6 and the second terminal of the sampling switch SW 12. During the first period of the reset phase, the switch SW61 is turned on, so the switch circuit 122 can short-circuit the output terminal pair of the gain circuit G1, thereby pulling the voltage pair of the sampling capacitor C5 and the sampling capacitor C6 to the specific voltage (the level of the specific voltage is between the two original levels output from the output terminal pair of the gain circuit G1). During the second period of the reset phase, the switch SW61 is turned off, so the switch circuit 122 can stop affecting the output of the gain circuit G1 to the output voltage pair.
Fig. 7 is a circuit block diagram illustrating a switching circuit 122 according to another embodiment of the invention. The sensing circuit 110, the analog-to-digital converter (ADC)130, the amplifier AMP, and/or the offset voltage storage and reduction circuit 123 shown in fig. 7 can be described with reference to fig. 4 or fig. 5, and therefore are not repeated herein.
In the embodiment shown in FIG. 7, the switch circuit 122 includes a pair of switches (SW71 and SW 72). The first terminal of the switch SW71 is coupled to the first input terminal of the transconductance circuit 430 of the offset voltage storage and reduction circuit 123, and the second terminal of the switch SW71 is coupled to the reference voltage Vref2 (the specified voltage). The level of the reference voltage Vref2 can be determined according to design requirements. For example, the reference voltage Vref2 may be a common mode voltage or other reference voltage. The first terminal of the switch SW72 is coupled to the second input terminal of the transconductance circuit 430 of the offset voltage storage and reduction circuit 123, and the second terminal of the switch SW72 is coupled to the reference voltage Vref 2. During the first period of the reset phase, the switches SW71 and SW72 are turned on, so the switch circuit 122 can pull the voltage of the sampling capacitor C5 and the sampling capacitor C6 to the reference voltage Vref 2. During the second period of the reset phase, the switches SW71 and SW72 are turned off, so the switch circuit 122 can stop affecting the pair of output voltages outputted by the output terminal of the gain circuit G1.
In summary, the source driver of the embodiments of the invention has the switch circuit 122. The switch circuit 122 is coupled to an output terminal pair of one gain circuit of the amplifier circuit 121. In the reset phase, the switching circuit 122 may reset the output voltage of the pair of output terminals. Therefore, the source driver can reduce the influence of the pixel information of the previous pixel circuit on the pixel information of the current pixel circuit.
Although the present invention has been described with reference to the above embodiments, it should be understood that various changes and modifications can be made therein by those skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.
