阅读说明：本技术 一种电流dac电路和输出电流的方法 (current DAC circuit and current output method ) 是由 许泽华 孔庆河 卢伟鹏 程剑涛 杜黎明 孙洪军 乔永庆 于 2019-09-24 设计创作，主要内容包括：一种电流DAC电路和输出电流的方法,电路的线性DAC电路以获取到的指数基准电流和线性基准电流为基准,将输入至线性DAC电路的数字码经过线性数模转换后得到第一线性模拟电流信号和第二线性模拟电流信号,指数电流产生电路基于第一线性模拟电流信号和预设的最小期望输出电流生成指数电流并输出,将指数电流作为电流DAC电路的输出信号,或者是,线性DAC电路直接将第二线性模拟电流信号作为电流DAC电路的输出信号,用户可以依据自身需求选择线性DAC电路的输出信号,实现了电流DAC电路输出指数电流还是输出线性电流的自行选择,实现了电流DAC电路输出指数电流还是输出线性电流的自行选择。(A current DAC circuit and a method for outputting current are provided, a linear DAC circuit of the circuit takes obtained exponential reference current and linear reference current as references, digital codes input to the linear DAC circuit are subjected to linear digital-to-analog conversion to obtain a first linear analog current signal and a second linear analog current signal, an exponential current generating circuit generates and outputs exponential current based on the first linear analog current signal and preset minimum expected output current, the exponential current is taken as an output signal of the current DAC circuit, or the linear DAC circuit directly uses the second linear analog current signal as the output signal of the current DAC circuit, and a user can select the output signal of the linear DAC circuit according to the requirement of the user, so that the self-selection of the current DAC circuit for outputting the exponential current or the linear current is realized, and the self-selection of the current DAC circuit for outputting the exponential current or the linear current is realized.)

1. A current DAC circuit, comprising:

The linear DAC circuit is used for performing linear digital-to-analog conversion on a digital code input to the linear DAC circuit to obtain a first linear analog current signal and a second linear analog current signal by taking the obtained exponential reference current or linear reference current as a reference, wherein a first output end of the linear DAC circuit is used for outputting the first linear analog current signal, and a second output end of the linear DAC circuit is used for outputting the second linear analog current signal;

the exponential current generating circuit is used for acquiring a first linear analog current signal output by the linear DAC circuit and a preset minimum expected output current, and generating and outputting an exponential current based on the first linear analog current signal and the preset minimum expected output current;

a first node as an output terminal of the current DAC circuit, selectively outputting a second linear analog current signal output by the linear DAC circuit or an exponential current output by the exponential current generation circuit.

2. the current DAC circuit of claim 1 wherein the exponential reference current generation circuit comprises:

The first constant current source, the second constant current source, the first diode, the second diode and the transconductance amplifier;

the input end of the first diode is connected with the output end of the first constant current source and the non-inverting input end of the transconductance amplifier, and the output end of the first diode is grounded;

The input end of the second diode is connected with the output end of the second constant current source and the inverting input end of the transconductance amplifier, and the output end of the second diode is grounded;

The output end of the transconductance amplifier is used as the output end of the exponential reference current generating circuit;

The first constant current source is for providing the maximum desired output current and the second constant current source is for providing the minimum desired output current.

3. The current DAC circuit of claim 1 wherein the exponential current generation circuit comprises:

the input end of the buffer is used as the input end of the exponential current generating circuit;

a first end of the first resistor is connected to the input end of the buffer, and the input voltage of a second end of the first resistor is the terminal voltage of the second diode;

The input end of the third diode is connected with the output end of the buffer, and the output end of the third diode is grounded;

The drain electrode and the grid electrode of the first MOS tube are connected with the output end of the buffer, and the source electrode of the first MOS tube is connected with a third current source;

And the drain electrode of the second MOS tube is used as the output end of the exponential current generating circuit, the grid electrode of the second MOS tube is connected with the output end of the buffer, and the source electrode of the second MOS tube is connected with a third current source.

4. the current DAC circuit of claim 3 wherein the exponential current generation circuit outputs an exponential current of:

Wherein, the I_{o_exp}Is exponential current, said I_minfor the minimum desired output current, I_maxFor the maximum desired output current, the Code is a digital Code of the linear DAC circuit;

the second linear analog current signal output by the linear DAC circuit is:

said I_{o_lin}Is a second linear analog current signal.

5. the current DAC circuit of claim 3 further comprising a pull-down resistor, wherein the first node is coupled to ground through the pull-down resistor.

6. the current DAC circuit according to claim 3, wherein the transconductance coefficient gm of the transconductance amplifier is 1/R1, and the value of the R1 is the resistance value of the first resistor.

7. The current DAC circuit of claim 1, further comprising:

and the control signal output circuit is used for providing a first control signal and a second control signal which are complementary according to the acquired trigger instruction, wherein the first control signal is used for controlling the connection or disconnection between the linear DAC circuit and the first node, and the second control signal is used for controlling the connection or disconnection between the exponential current generation circuit and the first node.

8. the current DAC circuit of claim 1 wherein the output current of the linear reference current source is a maximum desired output current.

9. The current DAC circuit of claim 1, further comprising:

The output end of the exponential reference current generating circuit is connected with the input end of the linear DAC circuit, and the exponential reference current generating circuit is used for outputting and providing the exponential reference current for the linear DAC circuit based on a preset maximum expected output current and a preset minimum expected output current;

And the output end of the linear reference current source is connected with the input end of the linear DAC circuit, and the linear reference current source is used for providing the linear reference current for the linear DAC circuit.

10. the current DAC circuit of claim 9, further comprising:

a first control switch provided between the linear DAC circuit and the exponential reference current generation circuit, the first control switch being configured to control a conduction state between the linear DAC circuit and the exponential reference current generation circuit according to a first control signal;

A second control switch provided between the linear DAC circuit and the linear reference current source, the second control switch being configured to control a conduction state between the linear DAC circuit and the linear reference current source generation circuit according to a second control signal;

a third control switch disposed between the first output terminal of the linear DAC circuit and the exponential current generating circuit, or between the exponential current generating circuit and the first node, the third control switch being configured to control a conduction state between the first output terminal of the linear DAC circuit and the exponential current generating circuit, or between the exponential current generating circuit and the first node, according to the first control signal;

a fifth control switch disposed between the second output terminal of the linear DAC circuit and the first node, the fifth control switch being configured to control a conduction state between the second output terminal of the linear DAC circuit and the first node according to a second control signal.

11. a method for outputting current, which is applied to a linear DAC circuit, and comprises the following steps:

Taking the obtained exponential reference current or linear reference current as a reference, and performing linear digital-to-analog conversion on the digital code to obtain a first linear analog current signal and a second linear analog current signal;

Obtaining an exponential current according to the first linear analog current signal and a preset minimum expected output current;

Selecting one of the second linear analog current signal and the exponential current as an output current.

12. the method of outputting current according to claim 11,

The exponential current is generated based on the following formula:

Wherein, the I_{o_exp}is exponential current, said I_minFor minimum desired output current, I_maxthe Code is a digital Code of the linear DAC circuit at the maximum expected output current;

The second linear analog current signal is calculated based on the following formula:

Said I_{o_lin}is a second linear analog current signal.

13. an LED driving chip, characterized in that the current DAC circuit according to any one of claims 1 to 10 is applied.

Technical Field

The invention relates to the technical field of integrated circuits, in particular to a DAC circuit capable of configuring linear or exponential current and a method for outputting current.

Background

In recent years, with the development of science and technology and the improvement of living standard of people, digital products are widely applied. LCD screens are mostly used for screens of digital products, and the brightness control of the LCDs is adjusted by backlight LED driving chips. Since the human eye's perception of light is in the form of a logarithmic curve, i.e. more sensitive at low brightness, the more insensitive the brightness is. Therefore, the LED current regulation curve in the form of the index enables human eyes to sense light rays to be closer to linearity, is more comfortable in experience, and provides a healthy driving and protecting navigation for users with eyes, so that more and more LED driving chips at the high end of the main current adopt a linear or index current regulation scheme capable of supporting the users at the same time.

The prior art solutions mainly include two categories, digital and analog, which are exemplified separately here.

A DIGITAL scheme is presented in patent 1, APPATUS FOR IMPROVING THE ACCURACY OF AN EXPONTIAL CURRENT DIGITAL-TO-ANANGLOG (IDAC) USE A BINARY-WEIGHTED MSB. The scheme realizes an exponential current by realizing exponential mapping on MSB (MostSignificantBIT ) and LSB (Last) SignificantBIT (Least significant bit) parts of a regulation code (digital code of a linear DAC circuit) in a digital part;

a simulation scheme is mentioned in patent 2 "SYSTEM AND METHOD FOR the explicit two TO ANALOG CONVERSION". The scheme realizes exponential current by using an iterative addition method of output current in an analog part.

although the exponential current is realized in the scheme, the conversion or selection of the exponential current and the linear current cannot be realized.

disclosure of Invention

embodiments of the present invention provide a current DAC (Digital to analog converter) circuit and a method for outputting a current, so as to realize conversion or selection between an exponential current and a linear current.

In order to achieve the above purpose, the embodiments of the present invention provide the following technical solutions:

A current DAC circuit, comprising:

The linear DAC circuit is used for performing linear digital-to-analog conversion on a digital code input to the linear DAC circuit to obtain a first linear analog current signal and a second linear analog current signal by taking the obtained exponential reference current or linear reference current as a reference, wherein a first output end of the linear DAC circuit is used for outputting the first linear analog current signal, and a second output end of the linear DAC circuit is used for outputting the second linear analog current signal;

the exponential current generating circuit is used for acquiring a first linear analog current signal output by the linear DAC circuit and a preset minimum expected output current, and generating an exponential current based on the first linear analog current signal and the preset minimum expected output current;

A first node as an output terminal of the current DAC circuit, selectively outputting a second linear analog current signal output by the linear DAC circuit or an exponential current output by the exponential current generation circuit.

optionally, in the current DAC circuit, the exponential reference current generating circuit includes:

the first constant current source, the second constant current source, the first diode, the second diode and the transconductance amplifier;

the input end of the first diode is connected with the output end of the first constant current source and the non-inverting input end of the transconductance amplifier, and the output end of the first diode is grounded;

The input end of the second diode is connected with the output end of the second constant current source and the inverting input end of the transconductance amplifier, and the output end of the second diode is grounded;

the output end of the transconductance amplifier is used as the output end of the exponential reference current generating circuit;

the first constant current source is for providing the maximum desired output current and the second constant current source is for providing the minimum desired output current.

Optionally, in the current DAC circuit, the exponential current generating circuit includes:

The input end of the buffer is used as the input end of the exponential current generating circuit;

a first end of the first resistor is connected to the input end of the buffer, and the input voltage of a second end of the first resistor is the terminal voltage of the second diode;

The input end of the third diode is connected with the output end of the buffer, and the output end of the third diode is grounded;

the drain electrode and the grid electrode of the first MOS tube are connected with the output end of the buffer, and the source electrode of the first MOS tube is connected with a third current source;

and the drain electrode of the second MOS tube is used as the output end of the exponential current generating circuit, the grid electrode of the second MOS tube is connected with the output end of the buffer, and the source electrode of the second MOS tube is connected with a third current source.

optionally, in the current DAC circuit, the output current of the exponential current generating circuit is:

wherein, the I_minfor the minimum desired output current, the_maxFor the maximum desired output current, the Code is a digital Code of the linear DAC circuit;

The second linear analog current signal output by the linear DAC circuit is:

Optionally, in the current DAC circuit, the current DAC circuit further includes a pull-down resistor, and the first node is grounded through the pull-down resistor.

optionally, in the current DAC circuit, a transconductance coefficient gm of the transconductance amplifier is 1/R1, and a value of the R1 is a resistance value of the first resistor.

Optionally, the current DAC circuit further includes:

And the control signal output circuit is used for providing a first control signal and a second control signal which are complementary according to the acquired trigger instruction, wherein the first control signal is used for controlling the connection or disconnection between the linear DAC circuit and the first node, and the second control signal is used for controlling the connection or disconnection between the exponential current generation circuit and the first node.

optionally, in the current DAC circuit, an output current of the linear reference current source is a maximum desired output current.

Optionally, the current DAC circuit further includes:

the output end of the exponential reference current generating circuit is connected with the input end of the linear DAC circuit, and the exponential reference current generating circuit is used for outputting and providing the exponential reference current for the linear DAC circuit based on a preset maximum expected output current and a preset minimum expected output current;

the output end of the linear reference current source is connected with the input end of the linear DAC circuit, and the linear reference current source is used for providing the linear reference current for the linear DAC circuit;

Optionally, the current DAC circuit further includes:

a first control switch provided between the linear DAC circuit and the exponential reference current generation circuit, the first control switch being configured to control a conduction state between the linear DAC circuit and the exponential reference current generation circuit according to a first control signal;

A second control switch provided between the linear DAC circuit and the linear reference current source, the second control switch being configured to control a conduction state between the linear DAC circuit and the linear reference current source generation circuit according to a second control signal;

a third control switch disposed between the first output terminal of the linear DAC circuit and the exponential current generating circuit, the third control switch for controlling a conduction state between the first output terminal of the linear DAC circuit and the exponential current generating circuit according to a first control signal;

A fifth control switch disposed between the second output terminal of the linear DAC circuit and the first node, the fifth control switch being configured to control a conduction state between the second output terminal of the linear DAC circuit and the first node according to a second control signal.

A method for outputting current is applied to a linear DAC circuit, and comprises the following steps:

taking the obtained exponential reference current or linear reference current as a reference, and performing linear digital-to-analog conversion on the digital code to obtain a first linear analog current signal and a second linear analog current signal;

Obtaining an exponential current according to the first linear analog current signal and a preset minimum expected output current;

selecting one of the second linear analog current signal and the exponential current as an output current.

Optionally, in the method of outputting current described above,

the exponential current is generated based on the following formula:

wherein, the I_{o_exp}is exponential current, said I_minfor minimum desired output current, I_maxthe Code is a digital Code of the linear DAC circuit at the maximum expected output current;

the second linear analog current signal is calculated based on the following formula:

said I_{o_lin}is a second linear analog current signal.

an LED driving chip, which applies any one of the current DAC circuit.

Based on the above technical solution, in the above scheme provided in the embodiment of the present invention, the linear DAC circuit obtains the first linear analog current signal and the second linear analog current signal by performing linear digital-to-analog conversion on the digital code input to the linear DAC circuit with the obtained exponential reference current and the obtained linear reference current as references, the exponential current generating circuit generates an exponential current based on the first linear analog current signal and a preset minimum expected output current, and uses the exponential current as an output signal of the current DAC circuit, or the linear DAC circuit directly uses the second linear analog current signal as the output signal of the current DAC circuit, the embodiment of the invention can select the output signal of the linear DAC circuit according to the requirement and carry out necessary processing, realizes the conversion or self-selection of the output index current or the output linear current of the current DAC circuit, and realizes the self-selection purpose of the output index current or the output linear current of the current DAC circuit.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.

fig. 1 is a schematic structural diagram of a current DAC circuit according to an embodiment of the present disclosure;

Fig. 2 is a schematic structural diagram of a current DAC circuit according to another embodiment of the present application;

FIG. 3 is a diagram illustrating a relationship between an exponential current, a linear current, and a code of a linear DAC circuit according to an embodiment of the present disclosure;

fig. 4 is a schematic structural diagram of a buffer according to an embodiment of the present disclosure.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

referring to fig. 1, fig. 1 is a current DAC circuit provided in an embodiment of the present application, where the current DAC circuit includes:

linear DAC circuit 100 and exponential current generation circuit 300, specifically:

the linear DAC circuit 100 is configured to obtain a first linear analog current signal and a second linear analog current signal by taking the obtained exponential reference current and the obtained linear reference current as references and performing linear digital-to-analog conversion on a digital Code input to the linear DAC circuit 100, where a first output terminal of the linear DAC circuit 100 is configured to output the first linear analog current signal and a second output terminal of the linear DAC circuit 100 is configured to output the second linear analog current signal, where the linear DAC circuit 100 is a linear current DAC, and a resolution of the linear DAC circuit 100 may be selected according to a user requirement, for example, in the technical solution disclosed in this application, the resolution of the linear DAC circuit 100 is set to 11 bits (bit), that is, the digital Code input to the linear DAC circuit 100 may be represented as Code <10:0 >.

an exponential current generating circuit 300, an input end of the exponential current generating circuit 300 is configured to obtain a first linear analog current signal and a preset minimum expected output current Imin, where the first linear analog current signal and the preset minimum expected output current Imin can only be input by one, the first linear analog current signal and the minimum expected output current Imin are commonly loaded on the input end of the exponential current generating circuit 300, and the exponential current generating circuit 300 generates and outputs an exponential current based on the first linear analog current signal and the preset minimum expected output current Imin.

the first node O, which is an output terminal of the current DAC circuit, outputs the second linear analog current signal provided by the linear DAC circuit 100 or the exponential current provided by the exponential current generating circuit 300.

in the implementation of the technical solution disclosed in the above embodiment of the present application, the linear DAC circuit 100 obtains the first linear analog current signal and the second linear analog current signal by performing linear digital-to-analog conversion on the digital code input to the linear DAC circuit 100 with the acquired exponential reference current and linear reference current as references, the exponential current generating circuit 300 generates an exponential current based on the first linear analog current signal and a preset minimum expected output current Imin, and uses the exponential current as an output signal of the current DAC circuit, or the linear DAC circuit 100 directly uses the second linear analog current signal as an output signal of the current DAC circuit, and may select an output signal of the linear DAC circuit 100 according to its own requirements and perform necessary processing, so as to implement self-selection of whether the current DAC circuit outputs the exponential current or the output linear current.

the current DAC circuit provided in the embodiment of the present application may be configured with, in addition to the linear DAC circuit 100 and the exponential current generating circuit 300: an exponential reference current generating circuit 200, an exponential current generating circuit 300, a linear reference current source VCC0, a first control switch K1, a second control switch K2, a third control switch K3, a fourth control switch K4, and a fifth control switch K5.

the exponential reference current generating circuit 200 is configured to provide an exponential reference current to the linear DAC circuit 100, and specifically, an output terminal of the exponential reference current generating circuit 200 is connected to an input terminal of the linear DAC circuit 100, and the exponential reference current generating circuit 200 is configured to output the exponential reference current based on a preset maximum expected output current Imax and a preset minimum expected output current Imin, and provide the exponential reference current to the linear DAC circuit 100.

The linear reference current source VCC0 is configured to provide a linear reference current to the linear DAC circuit 100, and specifically, the output terminal of the linear reference current source VCC0 is connected to the input terminal of the linear DAC circuit 100, and the linear reference current source VCC0 is configured to provide a linear reference current to the linear DAC circuit 100.

The first control switch K1 is used for controlling the conducting state between the linear DAC circuit 100 and the exponential reference current generating circuit 200, specifically, the first control switch K1 is arranged between the linear DAC circuit 100 and the exponential reference current generating circuit 200, the first control switch K1 is used for controlling the conducting and disconnecting state between the linear DAC circuit 100 and the exponential reference current generating circuit 200 under the control of the first control signal sel, that is, the conducting and disconnecting state is switched, for example, when the first control signal sel is 1, the first control switch K1 is closed, the linear DAC circuit 100 and the exponential reference current generating circuit 200 are conducted, when the first control signal sel is 0, the first control switch K1 is opened, and the linear DAC circuit 100 and the exponential reference current generating circuit 200 are disconnected;

the second control switch K2 is used for controlling the conducting state between the linear DAC circuit 100 and the linear reference current source VCC0, specifically, the second control switch K2 is disposed between the linear DAC circuit 100 and the linear reference current source VCC0, the output of the linear reference current source VCC0 is the maximum desired output current Imax, and the second control switch K2 is used for controlling the conducting and disconnecting state between the linear DAC circuit 100 and the linear reference current source VCC0 generating circuit according to the second control signal sel; for example, when the second control signal sel is 1, the second control switch K2 is closed, the connection between the DAC circuit 100 and the circuit generating the linear reference current source VCC0 is made, and when the second control signal sel is 0, the second control switch K2 is opened, the connection between the DAC circuit 100 and the circuit generating the linear reference current source VCC0 is made disconnected;

the third control switch K3 is used for controlling the conduction state between the first output terminal of the linear DAC circuit 100 and the exponential current generating circuit 300, specifically, the third control switch K3 is disposed between the first output terminal of the linear DAC circuit 100 and the exponential current generating circuit 300, the third control switch K3 is used for controlling the conduction and disconnection state between the first output terminal of the linear DAC circuit 100 and the exponential current generating circuit 300 according to the first control signal, for example, when the first control signal sel is 1, the third control switch K3 is closed, the first output terminal of the linear DAC circuit 100 is conducted with the exponential current generating circuit 300, when the first control signal sel is 0, the third control switch K3 is opened, and the first output terminal of the linear DAC circuit 100 is disconnected with the exponential current generating circuit 300;

The fourth control switch K4 is used for controlling the conduction state between the output terminal of the exponential current generating circuit 300 and the first node O, and specifically, the fourth control switch K4 is arranged between the output terminal of the exponential current generating circuit 300 and the first node O, and the fourth control switch K4 is used for controlling the conduction and disconnection state between the output terminal of the exponential current generating circuit 300 and the first node O according to the first control signal;

the fifth control switch K5 is used for controlling the conducting state between the second output terminal of the linear DAC circuit 100 and the first node O, and specifically, the fifth control switch K5 is arranged between the second output terminal of the linear DAC circuit 100 and the first node O, and the fifth control switch K5 is used for controlling the conducting and disconnecting state between the second output terminal of the linear DAC circuit 100 and the first node O according to the second control signal, wherein, in the specific circuit design, the third control switch K3 and the fifth control switch K5 can be alternatively arranged, and of course, both can be arranged in the circuit according to the arrangement manner described above.

in the implementation of the technical solution disclosed in the above embodiment of the present application, the exponential reference current generating circuit 200 generates an exponential reference current, the linear reference current source VCC0 generates a linear reference current, the first control switch K1 and the second control switch K2 select whether the exponential reference current or the linear reference current is input to the linear DAC circuit 100, the linear DAC circuit 100 obtains a first linear analog current signal and a second linear analog current signal by performing a linear digital-to-analog conversion on a digital code input to the linear DAC circuit 100 with the obtained exponential reference current or the linear reference current as a reference, the fifth control switch K5 is opened when the third control switch K3 and the fourth control switch K4 are closed, the exponential current generating circuit 300 generates an exponential current based on the first linear analog current signal and a preset minimum desired output current Imin, and uses the exponential current as an output signal of the current DAC circuit, when the fifth control switch K5 is closed, the circuit where the third control switch K3 and the fourth control switch K4 are located is opened, the linear DAC circuit 100 directly uses the second linear analog current signal as the output signal of the current DAC circuit, and a user can control the on-state of the first control switch K1, the second control switch K2, the third control switch K3, the fourth control switch K4 and the fifth control switch K5 according to the own requirements through the first control signal and the second control signal, so that the self-selection of the exponential current output or the linear current output by the current DAC circuit is realized.

in addition, referring to fig. 2, the embodiment of the present application further specifically discloses a specific structure of an index reference current generating circuit 200 and an index current generating circuit 300, and referring to fig. 2, the index reference current generating circuit 200 includes:

A first constant current source VCC1, a second constant current source VCC2, a first diode D1, a second diode D2, and a transconductance amplifier a 1;

The input end of the first diode D1 is connected with the output end of the first constant current source VCC1 and the non-inverting input end of the transconductance amplifier A1, and the output end of the first diode D1 is grounded;

the input end of the second diode D2 is connected with the output end of the second constant current source VCC2 and the inverting input end of the transconductance amplifier a1, and the output end of the second diode D2 is grounded;

the output end of the transconductance amplifier a1 is used as the output end of the exponential reference current generating circuit 200 to output an exponential reference current Iexpr;

The first constant current source VCC1 is for providing a maximum desired output current Imax and the second constant current source VCC2 is for providing a minimum desired output current Imin.

the following derivation explains the operation principle of the linear DAC circuit 100:

first, from the V-I characteristic equation of the diode, the Vmax and Vmin equations in the circuit 1 can be derived as follows:

Wherein Imax is the maximum expected output current Imax provided by the first constant current source VCC1, Imin is the minimum expected output current Imin provided by the second constant current source VCC2, and Vmax is the maximum voltage at the end of the first diode D1; vmin is the minimum voltage at the end of the second diode D2; v_tis the thermoelectric potential of a diode; is reverse saturation current of the diode;

the calculation formula for obtaining the exponential reference current Iexpr provided by the exponential reference current generation circuit 200 based on the formula (1) and the formula (2) is as follows:

where R1 refers to the resistance of transconductance amplifier a 1.

taking the resolution of the linear DAC circuit 100 as 11bit as an example, the relationship between the input current Iin and the output current Io of the linear DAC circuit 100 with 11bit is known as follows:

Wherein code is the digital code of the linear DAC circuit 100;

in combination with equation 3, the calculation equations of the first linear analog current signal Io1 output by the linear DAC circuit 100 and the second linear analog current signal Io2 output by the linear DAC circuit 100 can be derived:

when the first control switch K1 is closed,

when the second control switch K2 is closed,

Referring to fig. 2, the exponential current generating circuit 300 includes:

A buffer A2, an input terminal of the buffer A2 being an input terminal of the exponential current generating circuit 300;

A first resistor R1, a first end of the first resistor R1 is connected to the input end of the buffer a2, an input voltage at a second end of the first resistor R1 is a terminal voltage (Vmin) of the second diode D2, and a second end of the first resistor R1 may be directly connected to the input end of the second diode D2 to obtain the Vmin, where, in circuit design, preferably, a resistance value of the first resistor R1 is the same as a resistance value of the transconductance amplifier a1, that is, a transconductance coefficient gm of the transconductance amplifier a1 is 1/R1, a value of R1 is a resistance value of the first resistor R1, where R1 denotes the first resistor R1, and also denotes resistances of the first resistor R1 and the transconductance amplifier a 1;

an input end of a third diode D3, an input end of a third diode D3 is connected with an output end of the buffer A2, and an output end of the third diode D3 is grounded;

a drain and a gate of the first MOS transistor M1 are connected with an output end of the buffer, and a source of the first MOS transistor M1 is connected with a third current source VCC 3;

the second MOS transistor M2, the drain of the second MOS transistor M2 is used as the output terminal of the exponential current generating circuit 300, the gate of the second MOS transistor M2 is connected to the output terminal of the buffer, and the source of the second MOS transistor M2 is connected to the third current source, wherein the first MOS transistor M1 and the second MOS transistor M2 form a 1:1 current mirror, and the types of the two switching transistors can be selected according to the user's requirements, for example, they may be PMOS switching transistors shown in the drawings, NMOS switching transistors, or triodes, and so on.

When sel is 1, Io1 generates a voltage drop on the resistor R1, and after the voltage Vmin below the resistor is superimposed, the calculation formula of Vo can be obtained as follows:

Vo is the output voltage of the buffer A2, and since Vo is added to the diode D3, the exponential current Io _ exp can be calculated by the equation of the V-I characteristic of the diode as follows:

Is reverse saturation current of the third diode, Vo Is output voltage of the buffer, V_tFor the thermoelectric voltage of the third diode, when sel is 0, Io2 is directly output, and the linear current Io _ lin can be calculated as:

as can be seen from the above linear current Io _ lin equation (9) and exponential current Io _ exp equation (8), the scheme switches the on states of the first control switch K1 to the fifth control switch K5 through the first control signal sel and the second control signal sel, so that the exponential and linear conversion from the digital dimming code to the output current can be realized. For example, if Imin is 50uA and Imax is 20mA, the formula of the exponential current and the linear current can be obtained as follows:

I_{o_exp}＝50uA×1.00293124^Code (10)

I_{o_lin}＝9.77uA×Code (11)

when Imin is 50uA and Imax is 20mA, the exponential current and the linear current trend, and the relationship between the two and the dimming Code of the linear DAC circuit 100 are shown in fig. 3.

in addition to the above structure, referring to fig. 4, the present application also discloses a specific structural schematic diagram of a buffer a2, referring to fig. 4, the buffer a2 includes:

A third constant current source VCC 3;

a bias trimmer A3 connected to a third constant current source VCC 3;

a first triode Q1 connected with the first output end of the bias trimmer A3, wherein the base electrode of the first triode Q1 is used for acquiring a first input signal INN signal input to the buffer, and the emitting electrode of the first triode Q1 is connected with the first output end of the bias trimmer A3;

A second triode Q2 connected to the second output terminal of the bias trimmer A3, a base of the second triode Q2 being connected to the second output terminal of the bias trimmer A3 for obtaining a second input signal INP signal input to the buffer, an emitter of the second triode Q2 being connected to the second output terminal of the bias trimmer A3, the first triode Q1 and the second triode Q2 being specifically bipolar junction transistors;

A third MOS transistor M3, a fifth MOS transistor M5, a seventh MOS transistor M7, and a ninth MOS transistor M9, which are connected in series in sequence, specifically, a drain of the third MOS transistor M3 is connected to a source of the fifth MOS transistor M5, a drain of the fifth MOS transistor M5 is connected to a drain of the seventh MOS transistor M7, and a source of the seventh MOS transistor M7 is connected to a drain of the ninth MOS transistor M9; the source electrode of the third MOS transistor M3 is grounded, and the source electrode of the ninth MOS transistor M9 is connected with a direct-current power supply;

A fourth MOS transistor M4, a sixth MOS transistor M6, an eighth MOS transistor M8, and a tenth MOS transistor M10 that are connected in series in sequence, specifically, a drain of the fourth MOS transistor is connected to a source of the sixth MOS transistor M6, a drain of the sixth MOS transistor is connected to a drain of the eighth MOS transistor M8, and a source of the eighth MOS transistor is connected to a drain of the tenth MOS transistor M10; the source electrode of the fourth MOS transistor M4 is grounded, and the source electrode of the tenth MOS transistor M10 is connected with a direct-current power supply;

the drain electrode of the fifth MOS transistor M5 is further connected to the gate electrodes of the third MOS transistor M4 and the fourth MOS transistor M4;

And one end of a compensation capacitor C1 and one end of a compensation capacitor C1 are connected with the common end of the sixth open MOS tube and the eighth open MOS tube, and the other end of the compensation capacitor C1 is grounded.

in the above-provided buffer a2 structure, the first transistor Q1 and the second transistor Q2 are input pair transistors, the MOS transistors M3-M10 form a folded cascode output stage, and the compensation capacitor C1 is an output compensation capacitor. The error of precision mainly comes from offset voltage, and this circuit has carried out two points to offset voltage optimization: 1) the input geminate transistors are bipolar junction transistors, and because the offset of the bipolar junction transistors is naturally smaller than that of MOS transistors, and the main source of offset voltage is the input geminate transistors, the offset voltage can be reduced to a greater extent by adopting BJT transistors as the input geminate transistors; 2) an offset trimming A3(offset trimming module) is added in the circuit, the offset trimming module can trim the offset of each chip according to the measurement result in the production stage, and the precision of the offset trimming A3 can be determined by the compromise according to the circuit area and the performance requirement.

in addition to the above structure, in order to facilitate a user to control the current states of the first signal and the second signal according to the user's own needs, in the technical solution disclosed in the above embodiment of the present application, the method may further include: the control signal output circuit is used for providing a first control signal and a second control signal according to the acquired trigger instruction, wherein the control signals output by the control signal output circuit are complementary signals, namely, when one of the signals is in a first state for controlling the control switch to be closed, the other signal is in a second state for controlling the control switch to be opened.

corresponding to the circuit, the application also discloses a method for outputting current, which is applied to an exponential current generation circuit and comprises the following steps:

When the exponential reference current or linear reference current input by the exponential current generation circuit is detected as a reference, the obtained exponential reference current or linear reference current is used as a reference, and digital codes are subjected to linear digital-to-analog conversion to obtain a first linear analog current signal and a second linear analog current signal; obtaining an exponential current according to the first linear analog current signal and a preset minimum expected output current; selecting one of the second linear analog current signal and the exponential current as an output current.

in the above method, the exponential current is based on a formulaCalculated, the second linear analog current signal is based on a formulaand (4) calculating.

wherein, the I_{o_exp}is exponential current, said I_minfor minimum desired output current, I_maxFor maximum desired output current, the Code is the digital Code of the linear DAC circuit, I_{o_lin}Is a second linear analog current signal.

corresponding to the current DAC circuit, the embodiment of the present application further discloses a driving chip using the current DAC circuit, where the driving chip may be an LED driving chip or a driving chip for driving other loads.

In the present specification, a plurality of embodiments are described, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other.

the previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.