Pixel signal compensation circuit, image sensor, and electronic device

Abstract

The application discloses a pixel signal compensation circuit, an image sensor and electronic equipment, and the circuit comprises: a pixel circuit unit, which is used for photoelectric conversion of an input light signal and outputs a converted voltage; a first current source, which is used for providing an adjustable first current signal; a second current source, which is used for providing an adjustable second current signal; one end of a switch unit is connected with an output end of the pixel circuit unit, and the other end of the switch unit is switchably connected with the first current source or the second current source, so as to selectively connect the first current source or the second current source to the pixel circuit unit. The circuit can adjust the current values of the first current source and the second current source, and control the on and off of the transmission switch tube, the reset transistor, the first source follower transistor and the first selection transistor, so as to generate a positive or negative compensation signal, compensate the converted voltage, and meet the requirements of a rear-end analog signal processing module.

Description

Technical Field

[0001] This invention relates to the field of image sensor technology, and in particular to a pixel signal compensation circuit, an image sensor, and an electronic device. Background Technology

[0002] An image sensor is a photoelectric conversion device used to convert light signals into converted voltage signals. After various processing steps, the converted voltage signals are output to a back-end chip, which then performs image reconstruction and displays the image on a display device.

[0003] Because of the correlated double sampling circuit used in the pixel, the conversion voltage uses the difference between the reset level and the signal level, i.e., the reset level minus the signal level. Due to the presence of noise, in low light conditions, the reset level may be lower than the signal level, resulting in a negative conversion voltage. Since a negative conversion level cannot be quantized, a compensation signal needs to be added to the conversion level.

[0004] Existing technologies typically add a compensation signal at the back-end digital stage. This compensation signal is usually only set to a positive value, and its sign and magnitude cannot be adjusted. This lack of adjustment flexibility cannot adequately meet the voltage conversion requirements of the back-end analog signal processing module. Summary of the Invention

[0005] The present invention aims to at least solve one of the technical problems existing in the prior art. Therefore, the object of the present invention is to provide a pixel signal compensation circuit, an image sensor, and an electronic device.

[0006] The present invention proposes a pixel signal compensation circuit, comprising:

[0007] A pixel circuit unit, which is used to perform photoelectric conversion on the input optical signal and output a conversion voltage;

[0008] A first current source is used to provide an adjustable first current signal;

[0009] A second current source is used to provide an adjustable second current signal;

[0010] A switching unit, one end of which is connected to the output terminal of the pixel circuit unit, and the other end of which can be switched to be connected to the first current source or the second current source, so as to selectively connect the first current source or the second current source to the pixel circuit unit to perform voltage compensation on the conversion voltage output by the pixel circuit unit.

[0011] In addition, the pixel signal compensation circuit according to embodiments of the present invention may also have the following additional technical features:

[0012] Furthermore, the pixel circuit unit includes:

[0013] A photodiode, wherein the anode of the photodiode is grounded;

[0014] A transmission switch transistor, the first end of which is connected to the cathode of the photodiode;

[0015] A reset transistor, wherein the first terminal of the reset transistor is connected to the second terminal of the transmission switch transistor, and the second terminal of the reset transistor is connected to the voltage input terminal;

[0016] A first source follower transistor, the first terminal of the first source follower transistor is connected to the voltage input terminal, and the control terminal of the first source follower transistor is connected to the second terminal of the transmission switch and the first terminal of the reset transistor respectively.

[0017] A first selection transistor, wherein a first terminal of the first selection transistor is connected to a second terminal of the first source follower transistor, and the second terminal of the first selection transistor is connected to one end of the switching unit;

[0018] The switching unit switches between the first current source and the second current source, causing the second terminal of the first source follower transistor to output a first current signal or a second current signal, and a compensation signal is obtained based on the first current signal and the second current signal, so as to compensate the conversion voltage according to the compensation signal.

[0019] Further, the switching unit is switched to one of the first current source and the second current source, so that the first selection transistor is turned on under the control of the first control signal line, and the transmission switch and the reset transistor are turned on under the control of the second control signal line and the third control signal line, respectively, so as to reset the photodiode. After that, the transmission switch and the reset transistor are turned off under the control of the second control signal line and the third control signal line, respectively. After a first preset time, the reset transistor is turned on under the control of the third control signal line, so as to reset the control terminal of the first source follower transistor. After that, the reset transistor is turned off under the control of the third control signal line, so as to obtain the first reset voltage output by the first selection transistor.

[0020] Switch the switching unit to the other of the first current source and the second current source. After the transmission switch is turned on for a second preset time under the control of the second control signal line, the transmission switch is turned off under the control of the second control signal line to obtain the first signal voltage output by the first selection transistor.

[0021] The difference between the first reset voltage and the first signal voltage is used as the compensated conversion voltage, and the compensated conversion voltage is output.

[0022] Furthermore, the pixel circuit unit further includes:

[0023] The second source follower transistor has its first terminal connected to the voltage input terminal, and its control terminal is connected to the second terminal of the transmission switch, the first terminal of the reset transistor, and the control terminal of the first source follower transistor.

[0024] The second selection transistor has a first terminal connected to the second terminal of the second source follower transistor, and the second terminal of the second selection transistor is connected to the first current source.

[0025] The switching unit switches between the first current source and the second current source to compensate the conversion voltage based on the threshold voltage difference between the first source follower transistor and the second source follower transistor and the compensation signal.

[0026] Furthermore, the switching unit is switched to the second current source, causing the first selection transistor to turn off under the control of the first control signal line, and the second selection transistor to turn on under the control of the fourth control signal line;

[0027] The transmission switch and the reset transistor are turned on under the control of the second control signal line and the third control signal line, respectively, to reset the photodiode. After that, the transmission switch and the reset transistor are turned off under the control of the second control signal line and the third control signal line, respectively. After a third preset time, the control terminal of the second source follower transistor is reset, and the reset transistor is turned off under the control of the third control signal line to obtain the second reset voltage currently output by the second selection transistor. The first selection transistor is turned on under the control of the first control signal line, and the second selection transistor is turned off under the control of the fourth control signal line. After the transmission switch is turned on for a fourth preset time, the transmission switch is turned off under the control of the second control signal line to obtain the second signal voltage currently output by the first selection transistor.

[0028] The difference between the second reset voltage and the second signal voltage is used as the compensated conversion voltage, and the compensated conversion voltage is output.

[0029] Furthermore, the switching unit is switched to the second current source, so that the first selection transistor is turned on under the control of the first control signal line, and the second selection transistor is turned off under the control of the fourth control signal line;

[0030] The transmission switch and the reset transistor are turned on under the control of the second control signal line and the third control signal line, respectively, to reset the photodiode. After that, the transmission switch and the reset transistor are turned off under the control of the second control signal line and the third control signal line, respectively. After a fifth preset time, the control terminal of the first source follower transistor is reset, and the reset transistor is turned off under the control of the third control signal line to obtain the third reset voltage output by the second selection transistor. The first selection transistor is turned off under the control of the first control signal line, and the second selection transistor is turned on under the control of the fourth control signal line. After a sixth preset time when the transmission switch is turned on, the transmission switch is turned off under the control of the second control signal line to obtain the third signal voltage output by the second selection transistor.

[0031] The difference between the third reset voltage and the third signal voltage is used as the compensated conversion voltage, and the compensated conversion voltage is output.

[0032] Further, the switching unit is switched to one of the first current source and the second current source; causing the first selection transistor to be turned on under the control of the first control signal line, and the second selection transistor to be turned off under the control of the fourth control signal line;

[0033] The transmission switch and the reset transistor are turned on under the control of the second control signal line and the third control signal line, respectively, so that after the photodiode is reset, the transmission switch and the reset transistor are turned off under the control of the second control signal line and the third control signal line, respectively. After a seventh preset time, the control terminal of the first source follower transistor is reset, and the reset transistor is turned off under the control of the third control signal line to obtain the fourth reset voltage output by the first selection transistor.

[0034] Switch the switching unit to the other of the first current source and the second current source. After the transmission switch is turned on for an eighth preset time under the control of the second control signal line, turn the transmission switch off under the control of the second control signal line to obtain the fourth signal voltage output by the first selection transistor.

[0035] The difference between the fourth reset voltage and the fourth signal voltage is used as the compensated conversion voltage, and the compensated conversion voltage is output.

[0036] Furthermore, the voltage range of the compensation signal is 0–200 mV.

[0037] Furthermore, the threshold voltage difference between the first source follower transistor and the second source follower transistor is 100–200 mV.

[0038] According to an embodiment of the present invention, the pixel signal compensation circuit can adjust the current values ​​of the first current source and the second current source, or the threshold voltages of the first source follower transistor and the second source follower transistor, and generate positive or negative compensation signals by controlling the conduction and disconnection of the transmission switch transistor, the reset transistor, the first source follower transistor, the second source follower transistor, the first selection transistor, and the second selection transistor, to compensate the conversion voltage and meet the requirements of the back-end analog signal processing module.

[0039] To address the aforementioned problems, this invention also proposes an image sensor, comprising:

[0040] Pixel signal compensation circuit as described in any of the above embodiments.

[0041] According to an embodiment of the present invention, the image sensor can generate positive or negative compensation signals to compensate for the conversion voltage by adjusting the current values ​​of the first current source and the second current source, or the threshold voltages of the first source follower transistor and the second source follower transistor, and by controlling the conduction and disconnection of the transmission switch transistor, the reset transistor, the first source follower transistor, the second source follower transistor, the first selection transistor, and the second selection transistor, thereby well meeting the requirements of the back-end analog signal processing module.

[0042] To address the aforementioned problems, the present invention also proposes an electronic device, comprising:

[0043] Image sensors as described in any of the above embodiments.

[0044] According to an embodiment of the present invention, the electronic device can adjust the current values ​​of the first current source and the second current source, or the threshold voltages of the first source follower transistor and the second source follower transistor, and generate positive or negative compensation signals by controlling the conduction and disconnection of the transmission switch transistor, the reset transistor, the first source follower transistor, the second source follower transistor, the first selection transistor, and the second selection transistor, to compensate the conversion voltage and meet the requirements of the back-end analog signal processing module.

[0045] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0046] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0047] Figure 1 This is a schematic diagram of a pixel signal compensation circuit according to an embodiment of the present invention;

[0048] Figure 2 This is a pixel signal compensation circuit according to an embodiment of the present invention;

[0049] Figure 3 This is a pixel signal compensation circuit according to another embodiment of the present invention;

[0050] Figure 4 This is a schematic diagram of the process of obtaining the conversion voltage in a pixel signal compensation circuit according to an embodiment of the present invention;

[0051] Figure 5 This is a schematic diagram of the process of obtaining the conversion voltage in a pixel signal compensation circuit according to another embodiment of the present invention;

[0052] Figure 6 This is a schematic diagram of the process of obtaining the conversion voltage in a pixel signal compensation circuit according to another embodiment of the present invention;

[0053] Figure 7 This is a schematic diagram illustrating the relationship between different current source selections for pixels according to another embodiment of the present invention;

[0054] Figure 8 This is a schematic diagram of the process of obtaining the conversion voltage in a pixel signal compensation circuit according to another embodiment of the present invention. Detailed Implementation

[0055] The embodiments of the present invention are described in detail below. The embodiments described with reference to the accompanying drawings are exemplary. The embodiments of the present invention are described in detail below.

[0056] The following is for reference. Figures 1-8 A pixel signal compensation circuit and its control method, an image sensor, and an electronic device according to embodiments of the present invention are described.

[0057] Example 1

[0058] Figure 1 This is a pixel signal compensation circuit according to an embodiment of the present invention, such as... Figure 1 As shown, the pixel signal compensation circuit 10 includes: a pixel circuit unit 11, a first current source 12, a second current source 13, and a switching unit 14.

[0059] The pixel circuit unit 11 is used to perform photoelectric conversion on the input optical signal and output the conversion voltage.

[0060] The first current source 12 is used to provide an adjustable first current signal.

[0061] The second current source 13 is used to provide an adjustable second current signal.

[0062] One end of the switching unit 14 is connected to the output end of the pixel circuit unit, and the other end of the switching unit 14 can be switched to be connected to the first current source 12 or the second current source 13, so as to selectively connect the first current source 12 or the second current source 13 to the pixel circuit unit 11 to perform voltage compensation on the conversion voltage output by the pixel circuit unit 11.

[0063] In one embodiment of the present invention, the pixel circuit unit 11 includes: a photodiode, a transmission switch, a reset transistor, a first source follower transistor, and a first selection transistor.

[0064] In this case, the anode of the photodiode is grounded.

[0065] The first end of the transmission switch is connected to the cathode of the photodiode.

[0066] The first terminal of the reset transistor is connected to the second terminal of the transmission switch transistor, and the second terminal of the reset transistor is connected to the voltage input terminal, through which a preset voltage is input.

[0067] The first terminal of the first source follower transistor is connected to the voltage input terminal, and the control terminal of the first source follower transistor is connected to the second terminal of the transmission switch transistor and the first terminal of the reset transistor, respectively.

[0068] The first terminal of the first selection transistor is connected to the second terminal of the first source follower transistor, and the second terminal of the first selection transistor is connected to one terminal of the switching unit.

[0069] The switching unit switches between a first current source and a second current source, so that the second terminal of the first source following transistor outputs a first current signal or a second current signal, and a compensation signal is obtained based on the first current signal and the second current signal, so as to compensate the conversion voltage according to the compensation signal.

[0070] Specifically, the pixel signal compensation circuit of the above embodiment 1 sets two adjustable first current sources or second current sources at the pixel output end for switchable operation. At the first sampling reset level and the second sampling signal level of 4T pixel-related double sampling, the switching unit switches between the first current source and the second current source. That is, the first sampling reset level and the second sampling signal level correspond to different fixed current values ​​of the current sources. Different current values ​​will be superimposed between the control terminal of the first source follower transistor and the second terminal, and a compensation signal will be superimposed. This signal can be adjusted by changing the size of the current source. This signal can be regarded as the compensation signal of the pixel output signal.

[0071] Considering factors such as driving capability, the current value of the first or second current source cannot be adjusted arbitrarily, but only within a certain range. This adjustment range will result in a relatively small range for the compensation signal, for example, 0–200 mV. When a larger compensation voltage is required, it can be achieved through Embodiment 2 of the present invention.

[0072] As a specific embodiment, the following is combined with Figure 2 The pixel signal compensation circuit in a specific embodiment is described by way of example to provide a better understanding of the pixel signal compensation circuit in the embodiment of the present invention.

[0073] In a specific embodiment, such as Figure 2 As shown, the pixel signal compensation circuit includes a photodiode 21, a transmission switch 22, a reset transistor 23, a first source follower transistor 24, a first selection transistor 25, a switching unit 26, a first current source I1, and a second current source I2.

[0074] The transmission switch 22 is connected to the second control signal line and the photodiode 21. In response to the control of the second control signal provided by the second control signal line, it is used to transmit the electrical signal generated by the photodiode 21 to the control terminal of the first source follower transistor 24.

[0075] The reset transistor 23 is connected to the third control signal line, the voltage signal VDDP input to the voltage input terminal, and the transmission switch 22. In response to the control of the third control signal provided by the third control signal line, it is used to reset the photodiode 21.

[0076] The first terminal of the first source follower transistor 24 is connected to the voltage signal VDDP input to the voltage input terminal, and is used to output a corresponding current signal according to the voltage of the control terminal.

[0077] One end of the switching unit 26 is connected to the first selection transistor 25, and the other end of the switching unit 26 is connected to the first current source I1 or the second current source I2, so that the current signal output by the second electrode of the first source following the transistor 24 switches between the first current signal and the second current signal.

[0078] The first selection transistor 25 is connected to the second terminal of the first source follower transistor 24 and the first control signal line. In response to the control of the first control signal provided by the first control signal line, it is used to control the on / off connection between the second terminal of the first source follower transistor 24 and the image processor. When the second terminal of the first source follower transistor 24 outputs a first current signal or a second current signal, it outputs a corresponding first voltage signal or a second voltage signal. That is, when the other end of the switching unit 26 is connected to the first current source I1, the second terminal of the first selection transistor 25 outputs a first voltage signal; when the other end of the switching unit 26 is connected to the second current source I2, the second terminal of the first selection transistor 25 outputs a second voltage signal. Thus, a compensation signal is obtained according to the first current signal and the second current signal, so as to compensate the conversion voltage according to the compensation signal.

[0079] like Figure 4 As shown, the process of obtaining the conversion voltage by the pixel signal compensation circuit in Embodiment 1 above is described as follows:

[0080] S10: Switch the switching unit 14 to one of the first current source 12 and the second current source 13;

[0081] S11: The first selection transistor 25 is turned on under the control of the first control signal line, and the transmission switch 22 and the reset transistor 23 are turned on under the control of the second control signal line and the third control signal line, respectively, so that after the photodiode 21 is reset, the transmission switch 22 and the reset transistor 23 are turned off under the control of the second control signal line and the third control signal line, respectively. After a first preset time, the reset transistor 23 is turned on under the control of the third control signal line, so as to reset the control terminal of the first source follower transistor 24. After that, the reset transistor 23 is turned off under the control of the third control signal line, so as to obtain the first reset voltage output by the first selection transistor 25.

[0082] S12: Switch the switching unit 14 to the other of the first current source 12 and the second current source 13. After the transmission switch 22 is turned on under the control of the second control signal line for a second preset time, the transmission switch 22 is turned off under the control of the second control signal line to obtain the first signal voltage output by the first selection transistor 25.

[0083] S13: Use the difference between the first reset voltage and the first signal voltage as the compensated conversion voltage, and output the compensated conversion voltage.

[0084] As a specific embodiment, the following is combined with Figure 2 and Figure 7The working principle of the pixel signal compensation circuit in a specific embodiment is described by way of example to help to better understand the working principle of the pixel signal compensation circuit in the embodiment of the present invention.

[0085] That is to say Figure 7 Vr2 in the text refers to:

[0086]

[0087] Where I1 is the current value of current source I1, μ n It is electron mobility, C ox V is the gate oxide capacitance of the first source follower transistor, W / L is the width-to-length ratio of the first source follower transistor, and V is the gate oxide capacitance. th1 It is the threshold voltage of the first source follower transistor.

[0088] The process of acquiring the signal voltage is described as follows: The control switch unit 26 is switched to the second current source I2, causing the transmission switch transistor 22 to conduct under the control of the second control signal line for a second preset time. After this second preset time, the transmission switch transistor 22 is then turned off under the control of the second control signal line. The second preset time is the time required for all electrons in the photodiode 31 to travel to the control terminal of the first source follower transistor 34. The voltage output by the current first selection transistor 24 is then acquired as the signal voltage (i.e., the first signal voltage). Figure 7 Vs2 in the text refers to:

[0089]

[0090] Where I2 is the current value of current source I1, μ n It is electron mobility, C ox V is the gate oxide capacitance of the first source follower transistor, W / L is the width-to-length ratio of the first source follower transistor, and V is the gate oxide capacitance. th1 It is the threshold voltage of the first source follower transistor.

[0091] The difference between the first reset voltage and the first signal voltage is used as the compensated conversion voltage, and the output compensated conversion voltage is:

[0092] ΔV1=V r -V s =ΔV 光 +δV

[0093] Where δV is the compensation signal. ΔV 光 It is the voltage generated by the optical signal.

[0094] Similarly, under strong light conditions, when acquiring the reset voltage, the control switch unit 26 is switched to the second current source I2; when acquiring the signal voltage, the control switch unit 26 is switched to the first current source I1. The compensated conversion voltage is then:

[0095] ΔV2=V r -V s =ΔV 光 -δV

[0096] In summary, by switching between the first current source I1 or the second current source I2 through the switching unit 26, and controlling the conduction and disconnection of the transmission switch 22, the reset transistor 23, the first source follower transistor 24, and the first selection transistor 25, a positive or negative compensation signal δV can be obtained to compensate for the conversion voltage, thereby well meeting the requirements of the back-end analog signal processing module.

[0097] like Figure 7 As shown, Vr2 is the reset voltage in Embodiment 1 of the present invention, Vs2 is the signal voltage in Embodiment 1 of the present invention, Vr1 is the reset voltage without signal compensation, and Vs1 is the signal voltage without signal compensation. It can be seen that Embodiment 1 of the present invention can obtain a positive or negative compensation signal δV to compensate the conversion voltage, thereby well meeting the requirements of the back-end analog signal processing module.

[0098] Example 2

[0099] In one embodiment of the present invention, the pixel circuit unit further includes: a second source follower transistor and a second selection transistor.

[0100] The first terminal of the second source follower transistor is connected to the voltage input terminal, and the control terminal of the second source follower transistor is connected to the second terminal of the transmission switch, the first terminal of the reset transistor, and the control terminal of the first source follower transistor.

[0101] The first terminal of the second selection transistor is connected to the second terminal of the second source follower transistor, and the second terminal of the second selection transistor is connected to the first current source.

[0102] The switching unit switches between a first current source and a second current source to compensate the switching voltage based on the threshold voltage difference between the first source follower transistor and the second source follower transistor and a compensation signal.

[0103] Specifically, the pixel signal compensation circuit of Embodiment 2 of the present invention adds a second source follower transistor and a second selection transistor, so that a pixel has two output terminals connected to a first current source and a second current source respectively, so as to obtain the conversion level by acquiring the reset level and the signal level through separate channels. Furthermore, by adjusting the threshold voltages of the first current source and the second current source, the first source follower transistor and the second source follower transistor, a compensation value is added to the reset level or the signal level, so that the conversion level is compensated by an additional compensation value. Compared with Embodiment 1, this compensation value is greater than the difference between the threshold voltages of the first source follower transistor and the second source follower transistor, for example, 100 to 200 mV, so the range of the compensation value can reach 300 to 400 mV, which meets the range required for the compensation signal.

[0104] In a specific embodiment, under strong light conditions, the compensation value can be negative so that the obtained conversion level is within the input range of the back-end analog signal processing module, avoiding adverse phenomena such as front-end saturation.

[0105] As a specific embodiment, the following is combined with Figure 3 The pixel signal compensation circuit in a specific embodiment is described by way of example to provide a better understanding of the pixel signal compensation circuit in the embodiment of the present invention.

[0106] In a specific embodiment, such as Figure 3 As shown, the pixel signal compensation circuit includes a photodiode 31, a transmission switch 32, a reset transistor 33, a first source follower transistor 34, a second source follower transistor 37, a first selection transistor 35, a second selection transistor 38, a switching unit 36, a first current source I1, and a second current source I2.

[0107] The transmission switch 32 is connected to the second control signal line and the photodiode 31. In response to the control of the second control signal provided by the second control signal line, it is used to transmit the electrical signal generated by the photodiode 31 to the control terminal of the first source follower transistor 34 or the second source follower transistor 37.

[0108] The reset transistor 33 is connected to the third control signal line, the voltage signal VDDP input to the voltage input terminal, and the transmission switch 32. In response to the control of the third control signal provided by the third control signal line, it is used to reset the photodiode 31.

[0109] The first terminal of the first source follower transistor 34 is connected to the voltage signal VDDP input to the voltage input terminal, and is used to output a corresponding current signal according to the voltage of the control terminal.

[0110] One end of the switching unit 36 ​​is connected to the first selection transistor 35, and the other end of the switching unit 36 ​​is connected to the first current source I1 or the second current source I2, so that the current signal output from the second electrode of the first source follower transistor 34 or the second source follower transistor 37 is switched between the first current signal and the second current signal.

[0111] The first selection transistor 35 is connected to the second terminal of the first source follower transistor 34 and the first control signal line. In response to the control of the first control signal provided by the first control signal line, it is used to control the on / off connection between the second terminal of the first source follower transistor 34 and the image processor. When the second terminal of the first source follower transistor 34 outputs a first current signal or a second current signal, it outputs a corresponding first voltage signal or a second voltage signal. That is, when the other end of the switching unit 36 ​​is connected to the first current source I1, the second terminal of the first selection transistor 35 outputs a first voltage signal; when the other end of the switching unit 36 ​​is connected to the second current source I2, the second terminal of the first selection transistor 35 outputs a second voltage signal. Thus, a compensation signal is obtained according to the first current signal and the second current signal, so as to compensate the conversion voltage according to the compensation signal.

[0112] The first terminal of the second source follower transistor 37 is connected to the voltage signal VDDP input from the voltage input terminal. The control terminal of the second source follower transistor 37 is connected to the second terminal of the transmission switch transistor 32, the first terminal of the reset transistor 33, and the control terminal of the first source follower transistor 34, respectively.

[0113] The first terminal of the second selection transistor 38 is connected to the second terminal of the second source follower transistor 37, and the second terminal of the second selection transistor 38 is connected to the first current source I1.

[0114] The switching unit 36 ​​switches between the first current source I1 or the second current source I2 to compensate the switching voltage based on the threshold voltage difference between the first source follower transistor 34 and the second source follower transistor 37 and the compensation signal.

[0115] In one embodiment of the present invention, the voltage range of the compensation signal is 0 to 200 mV.

[0116] In one embodiment of the present invention, the threshold voltage difference between the first source follower transistor and the second source follower transistor is 100 to 200 mV.

[0117] Example 3

[0118] like Figure 5 As shown, under strong light conditions, the process of obtaining the conversion voltage by the pixel signal compensation circuit in Embodiment 2 above is described as follows:

[0119] S20: Switching unit 36 ​​switches to the second current source I2.

[0120] S21: The first selection transistor 35 is turned off under the control of the first control signal line, and the second selection transistor 38 is turned on under the control of the fourth control signal line.

[0121] S22: The transmission switch 32 and the reset transistor 33 are turned on under the control of the second control signal line and the third control signal line, respectively, to reset the photodiode 31. After that, the transmission switch 32 and the reset transistor 33 are turned off under the control of the second control signal line and the third control signal line, respectively. After a third preset time, the reset transistor 33 is controlled to reset the control terminal of the second source follower transistor 37. Then, the reset transistor 33 is turned off under the control of the third control signal line to obtain the second reset voltage output by the current second selection transistor 38. The first selection transistor 35 is turned on under the control of the first control signal line, the second selection transistor 38 is turned off under the control of the fourth control signal line, and the transmission switch 32 is turned on under the control of the second control signal line for a fourth preset time, and then turned off under the control of the second control signal line to obtain the second signal voltage output by the current first selection transistor 35.

[0122] S23: Use the difference between the second reset voltage and the second signal voltage as the compensated conversion voltage, and output the compensated conversion voltage.

[0123] As a specific embodiment, the following is combined with Figure 3 and Figure 7 The working principle of the pixel signal compensation circuit in a specific embodiment is described by way of example to help to better understand the working principle of the pixel signal compensation circuit in the embodiment of the present invention.

[0124] The process of obtaining the reset voltage is described as follows: the first selection transistor 35 is turned off under the control of the first control signal line, and the second selection transistor 38 is turned on under the control of the fourth control signal line; the transmission switch 32 and the reset transistor 33 are turned on under the control of the second control signal line and the third control signal line, respectively, to reset the photodiode 31. After that, the transmission switch 32 and the reset transistor 33 are turned off under the control of the second control signal line and the third control signal line, respectively. After an integration time (i.e., the third preset time), the reset transistor 33 is controlled to reset the control terminal of the second source follower transistor 37. Then, the reset transistor 33 is turned off under the control of the third control signal line. The voltage output by the second selection transistor 38 is obtained as the reset voltage (i.e., the second reset voltage). Figure 7 Vr3 in the text refers to:

[0125]

[0126] Where I2 is the current value of current source I2, μ n It is electron mobility, C ox This is the gate oxide capacitance of the second source follower transistor, W / L is the width-to-length ratio of the second source follower transistor, and V... th2 It is the threshold voltage of the second source follower transistor.

[0127] The process of acquiring the signal voltage is described as follows: the first selection transistor 35 is turned on under the control of the first control signal line; the second selection transistor 38 is turned off under the control of the fourth control signal line; the transmission switch 32 is turned on under the control of the second control signal line for a fourth preset time, and then turned off under the control of the second control signal line. The fourth preset time is the time required for all electrons in the photodiode 31 to be transferred to the control terminal of the first source follower transistor 34. The voltage currently output by the first selection transistor 35 is the signal voltage (i.e., the second signal voltage). Figure 7 Vs3 in the context is:

[0128]

[0129] Where I1 is the current value of current source I1, μ n It is electron mobility, C ox V is the gate oxide capacitance of the first source follower transistor, W / L is the width-to-length ratio of the first source follower transistor, and V is the gate oxide capacitance. th1 It is the threshold voltage of the first source follower transistor.

[0130] Using the difference between the second reset voltage and the second signal voltage as the compensated conversion voltage, the compensated conversion voltage is:

[0131]

[0132] Right now:

[0133] ΔV2=ΔV 光 -ΔV 补 ,in,

[0134] ΔV 补 =δV+δV th

[0135] δV th =V th1 -V th2

[0136]

[0137] In summary, according to Embodiment 3 of the present invention, the conversion voltage is compensated based on the threshold voltage difference between the first source follower transistor 34 and the second source follower transistor 37 and the compensation signal, i.e., δV. Furthermore, the transmission switch 32, reset transistor 33, first source follower transistor 34, second source follower transistor 37, first select transistor 35, and second select transistor 38 are controlled to turn on and off, thereby obtaining a negative compensation signal ΔV. 补 This compensates for the conversion voltage, thus well meeting the requirements of the back-end analog signal processing module.

[0138] Example 4

[0139] like Figure 6 As shown, in a dark environment, the process of obtaining the conversion voltage by the pixel signal compensation circuit in Embodiment 2 above is described as follows:

[0140] S30: Switching unit 36 ​​switches to the second current source I2.

[0141] S31: The first selection transistor 35 is turned on under the control of the first control signal line, and the second selection transistor 38 is turned off under the control of the fourth control signal line.

[0142] S32: The transmission switch 32 and the reset transistor 33 are turned on under the control of the second control signal line and the third control signal line, respectively, so that after the photodiode is reset, the transmission switch 32 and the reset transistor 33 are turned off under the control of the second control signal line and the third control signal line, respectively. After a fifth preset time, the reset transistor is controlled to reset the control terminal of the first source follower transistor. Then, the reset transistor 33 is turned off under the control of the third control signal line to obtain the third reset voltage output by the current first selected crystal 35.

[0143] S33: The first selection transistor 35 is turned off under the control of the first control signal line, the second selection transistor 38 is turned on under the control of the fourth control signal line, and the transmission switch 32 is turned on under the control of the second control signal line for a six-preset time, and then turned off under the control of the second control signal line to obtain the third signal voltage output by the second selection transistor 38.

[0144] S34: Use the difference between the third reset voltage and the third signal voltage as the compensated conversion voltage, and output the compensated conversion voltage.

[0145] As a specific embodiment, the following is combined with Figure 3 and Figure 7 The working principle of the pixel signal compensation circuit in a specific embodiment is described by way of example to help to better understand the working principle of the pixel signal compensation circuit in the embodiment of the present invention.

[0146] The process of obtaining the reset voltage is described as follows: the first selection transistor 35 is turned on under the control of the first control signal line, and the second selection transistor 38 is turned off under the control of the fourth control signal line; the transmission switch 32 and the reset transistor 33 are turned on under the control of the second control signal line and the third control signal line, respectively, to reset the photodiode 31. After that, the transmission switch 32 and the reset transistor 33 are turned off under the control of the second control signal line and the third control signal line, respectively. After an integration time (i.e., the fifth preset time), the reset transistor 33 is controlled to reset the control terminal of the first source follower transistor 34. Then, the reset transistor 33 is turned off under the control of the third control signal line. The voltage output by the first selection transistor 35 is obtained as the reset voltage (i.e., the third reset voltage). Figure 7 Vr3 in the text refers to:

[0147]

[0148] Where I2 is the current value of current source I2, μ n It is electron mobility, C ox V is the gate oxide capacitance of the first source follower transistor, W / L is the width-to-length ratio of the first source follower transistor, and V is the gate oxide capacitance. th2 It is the threshold voltage of the first source follower transistor.

[0149] The process of acquiring the signal voltage is described as follows: the first selection transistor 35 is turned off under the control of the first control signal line, the second selection transistor 38 is turned on under the control of the fourth control signal line, and the transmission switch 32 is turned on under the control of the second control signal line for a sixth preset time, and then turned off under the control of the second control signal line. The sixth preset time is the time required for all electrons in the photodiode 31 to be transferred to the control terminal of the second source follower transistor 34. The voltage currently output by the second selection transistor 35 is the signal voltage (i.e., the third signal voltage). Figure 7 Vs3 in the context is:

[0150]

[0151] Where I1 is the current value of current source I1, μ n It is electron mobility, C ox This is the gate oxide capacitance of the second source follower transistor, W / L is the width-to-length ratio of the second source follower transistor, and V... th2 This is the threshold voltage of the second source follower transistor. ΔV 光 It is the voltage generated by the optical signal.

[0152] Using the difference between the third reset voltage and the third signal voltage as the compensated conversion voltage, the compensated conversion voltage is:

[0153]

[0154] ΔV3=ΔV 光 +ΔV 补

[0155] in,

[0156] ΔV 补 =δV+δV th

[0157] δV th =V th1 -V th2

[0158] In summary, according to Embodiment 4 of the present invention, the conversion voltage is compensated based on the threshold voltage difference between the first source follower transistor 34 and the second source follower transistor 37 and the compensation signal, i.e., δV. Furthermore, the transmission switch 32, reset transistor 33, first source follower transistor 34, second source follower transistor 37, first select transistor 35, and second select transistor 38 are controlled to turn on and off, thereby obtaining a positive compensation signal ΔV. 补 This compensates for the conversion voltage, thus well meeting the requirements of the back-end analog signal processing module.

[0159] like Figure 7 As shown, Vr3 is the reset voltage in Embodiments 3 and 4 of the present invention, Vs3 is the signal voltage in Embodiments 3 and 4 of the present invention, Vr2 is the reset voltage in Embodiment 1 of the present invention, and Vs2 is the signal voltage in Embodiment 1 of the present invention. Therefore, it can be seen that Embodiments 3 and 4 of the present invention can obtain a positive or negative compensation signal ΔV. 补 The difference between the threshold voltages of the first and second source follower transistors, for example, 100 to 200 mV, is greater than δV in Example 1, thus the compensation value ΔV 补 The range can reach 300-400mV, which meets the range required for compensation signals.

[0160] Example 5

[0161] like Figure 8 As shown, in a dark environment, the process of obtaining the conversion voltage by the pixel signal compensation circuit in Embodiment 2 above is described as follows:

[0162] S40: Switch the switching unit 36 ​​to one of the first current source I1 and the second current source I2.

[0163] S41: The first selection transistor 35 is turned on under the control of the first control signal line, and the second selection transistor 38 is turned off under the control of the fourth control signal line.

[0164] S42: The transmission switch 32 and the reset transistor 33 are turned on under the control of the second control signal line and the third control signal line, respectively, so that after resetting the photodiode, they are turned off under the control of the second control signal line and the third control signal line. After a seventh preset time, the reset transistor is controlled to reset the control terminal of the first source follower transistor. Then, the reset transistor 33 is turned off under the control of the third control signal line to obtain the fourth reset voltage output by the current first selection transistor.

[0165] S43: Switch the switching unit 36 ​​to the other of the first current source I1 and the second current source I2, and after the transmission switch 32 is turned on for an eighth preset time under the control of the second control signal line, it is turned off under the control of the second control signal line to obtain the fourth signal voltage output by the first selection transistor 35.

[0166] S44: Use the difference between the fourth reset voltage and the fourth signal voltage as the compensated conversion voltage, and output the compensated conversion voltage.

[0167] As a specific embodiment, the following is combined with Figure 3 The working principle of the pixel signal compensation circuit in a specific embodiment is described by way of example to help to better understand the working principle of the pixel signal compensation circuit in the embodiment of the present invention.

[0168] In a specific embodiment, such as Figure 3 As shown, the first selection transistor 35 is turned on under the control of the first control signal line, and the second selection transistor 38 is turned off under the control of the fourth control signal line. In a dark environment, the process of obtaining the reset voltage is described as follows: the control switch unit 36 ​​is switched to the first current source I1. The transmission switch transistor 32 and the reset transistor 33 are turned on under the control of the second and third control signal lines, respectively, to reset the photodiode 31. After resetting, they are turned off under the control of the second and third control signal lines. After an integration time (i.e., the seventh preset time), the reset transistor 33 resets the control terminal of the first source follower transistor 35. Then, the reset transistor 33 is turned off under the control of the third control signal line. The voltage currently output by the first selection transistor 35 is the reset voltage (i.e., the fourth reset voltage).

[0169]

[0170] Where I1 is the current value of current source I1, μ n It is electron mobility, C ox V is the gate oxide capacitance of the first source follower transistor, W / L is the width-to-length ratio of the first source follower transistor, and V is the gate oxide capacitance. th1 It is the threshold voltage of the first source follower transistor.

[0171] The process of acquiring the signal voltage is described as follows: the control switch unit 36 ​​switches to the second current source I2, and the transmission switch transistor 32 is turned on under the control of the second control signal line for an eighth preset time, and then turned off under the control of the second control signal line. The eighth preset time is the time required for all electrons in the photodiode 31 to be transferred to the control terminal of the first source follower transistor 35. The voltage output by the first selection transistor 35 is the signal voltage (i.e., the fourth signal voltage).

[0172]

[0173] Where I1 is the current value of current source I1, μ n It is electron mobility, C ox This is the gate oxide capacitance of the second source follower transistor, W / L is the width-to-length ratio of the first source follower transistor, and V... th1 This is the threshold voltage of the first source follower transistor. ΔV 光 It is the voltage generated by the optical signal.

[0174] The difference between the first reset voltage and the first signal voltage is used as the compensated conversion voltage, and the output compensated conversion voltage is:

[0175] ΔV4=V r -V s =ΔV 光 +δV

[0176] Where δV is the compensation signal.

[0177] Similarly, under strong light conditions, when acquiring the reset voltage, the control switch unit 26 is switched to the second current source I2; when acquiring the signal voltage, the control switch unit 26 is switched to the first current source I1. The compensated conversion voltage is then:

[0178] ΔV2=V r -V s =ΔV 光 -δV

[0179] In summary, by switching between the first current source I1 or the second current source I2 through the switching unit 36, and controlling the conduction and disconnection of the transmission switch 32, the reset transistor 33, the first source follower transistor 34, and the first selection transistor 35, a positive or negative compensation signal δV can be obtained to compensate for the conversion voltage, thereby well meeting the requirements of the back-end analog signal processing module.

[0180] The conversion voltage obtained in Embodiment 5 of the present invention is the same as that in Embodiment 1, that is, Embodiment 5 is compatible with Embodiment 1. The compensation voltage δV can be adjusted by adjusting the current values ​​of the first current source and the second current source.

[0181] According to an embodiment of the present invention, the pixel signal compensation circuit can generate positive or negative compensation signals to compensate for the conversion voltage by adjusting the current values ​​of the first current source I1 and the second current source I2, or the threshold voltages of the first source follower transistor 34 and the second source follower transistor 37, and by controlling the conduction and disconnection of the transmission switch transistor 32, the reset transistor 33, the first source follower transistor 34, the second source follower transistor 37, the first selection transistor 35, and the second selection transistor 38, thereby well meeting the requirements of the back-end analog signal processing module.

[0182] A further embodiment of the present invention also discloses an image sensor.

[0183] In some embodiments, the image sensor includes a pixel signal compensation circuit as described in any of the above embodiments.

[0184] According to an embodiment of the present invention, the image sensor can generate positive or negative compensation signals to compensate for the conversion voltage by adjusting the current values ​​of the first current source and the second current source, or the threshold voltages of the first source follower transistor and the second source follower transistor, and by controlling the conduction and disconnection of the transmission switch transistor, the reset transistor, the first source follower transistor, the second source follower transistor, the first selection transistor, and the second selection transistor, thereby well meeting the requirements of the back-end analog signal processing module.

[0185] Further embodiments of the present invention disclose an electronic device comprising:

[0186] Image sensors as described in any of the above embodiments.

[0187] According to an embodiment of the present invention, the electronic device can generate positive or negative compensation signals to compensate for the conversion voltage by adjusting the current values ​​of the first current source and the second current source, or the threshold voltages of the first source follower transistor and the second source follower transistor, and by controlling the conduction and disconnection of the transmission switch transistor, the reset transistor, the first source follower transistor, the second source follower transistor, the first selection transistor, and the second selection transistor, thereby well meeting the requirements of the back-end analog signal processing module.

[0188] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example.

[0189] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A pixel signal compensation circuit, applied to a correlation double sampling circuit, characterized in that, include: A pixel circuit unit, which is used to perform photoelectric conversion on the input optical signal and output a conversion voltage; A first current source is used to provide an adjustable first current signal; A second current source is used to provide an adjustable second current signal; A switching unit, one end of which is connected to the output terminal of the pixel circuit unit, and the other end of which can be switched to be connected to the first current source or the second current source, so as to selectively connect the first current source or the second current source to the pixel circuit unit to perform voltage compensation on the conversion voltage output by the pixel circuit unit.

2. The pixel signal compensation circuit according to claim 1, characterized in that, The pixel circuit unit includes: A photodiode, wherein the anode of the photodiode is grounded; A transmission switch transistor, the first end of which is connected to the cathode of the photodiode; A reset transistor, wherein the first terminal of the reset transistor is connected to the second terminal of the transmission switch transistor, and the second terminal of the reset transistor is connected to the voltage input terminal; A first source follower transistor, the first terminal of the first source follower transistor is connected to the voltage input terminal, and the control terminal of the first source follower transistor is connected to the second terminal of the transmission switch and the first terminal of the reset transistor respectively. A first selection transistor, wherein a first terminal of the first selection transistor is connected to a second terminal of the first source follower transistor, and the second terminal of the first selection transistor is connected to one end of the switching unit; The switching unit switches between the first current source and the second current source, causing the second terminal of the first source follower transistor to output a first current signal or a second current signal, and a compensation signal is obtained based on the first current signal and the second current signal, so as to compensate the conversion voltage according to the compensation signal.

3. The pixel signal compensation circuit according to claim 2, characterized in that, The switching unit is switched to one of the first current source and the second current source, so that the first selection transistor is turned on under the control of the first control signal line, the transmission switch and the reset transistor are turned on under the control of the second control signal line and the third control signal line, respectively, to reset the photodiode. After that, the transmission switch and the reset transistor are turned off under the control of the second control signal line and the third control signal line, respectively. After a first preset time, the reset transistor is turned on under the control of the third control signal line to reset the control terminal of the first source follower transistor. After that, the reset transistor is turned off under the control of the third control signal line to obtain the first reset voltage output by the first selection transistor. Switch the switching unit to the other of the first current source and the second current source. After the transmission switch is turned on for a second preset time under the control of the second control signal line, the transmission switch is turned off under the control of the second control signal line to obtain the first signal voltage output by the first selection transistor. The difference between the first reset voltage and the first signal voltage is used as the compensated conversion voltage, and the compensated conversion voltage is output.

4. The pixel signal compensation circuit according to claim 2, characterized in that, Also includes: The second source follower transistor has its first terminal connected to the voltage input terminal, and its control terminal is connected to the second terminal of the transmission switch, the first terminal of the reset transistor, and the control terminal of the first source follower transistor. The second selection transistor has a first terminal connected to the second terminal of the second source follower transistor, and the second terminal of the second selection transistor is connected to the first current source. The switching unit switches between the first current source and the second current source to compensate the conversion voltage based on the threshold voltage difference between the first source follower transistor and the second source follower transistor and the compensation signal.

5. The pixel signal compensation circuit according to claim 4, characterized in that, Switch the switching unit to the second current source, so that the first selection transistor is turned off under the control of the first control signal line, and the second selection transistor is turned on under the control of the fourth control signal line; The transmission switch and the reset transistor are turned on under the control of the second control signal line and the third control signal line, respectively, to reset the photodiode. After that, the transmission switch and the reset transistor are turned off under the control of the second control signal line and the third control signal line, respectively. After a third preset time, the control terminal of the second source follower transistor is reset, and the reset transistor is turned off under the control of the third control signal line to obtain the second reset voltage currently output by the second selection transistor. The first selection transistor is turned on under the control of the first control signal line, and the second selection transistor is turned off under the control of the fourth control signal line. After the transmission switch is turned on for a fourth preset time, the transmission switch is turned off under the control of the second control signal line to obtain the second signal voltage currently output by the first selection transistor. The difference between the second reset voltage and the second signal voltage is used as the compensated conversion voltage, and the compensated conversion voltage is output.

6. The pixel signal compensation circuit according to claim 4, characterized in that, Switch the switching unit to the second current source, so that the first selection transistor is turned on under the control of the first control signal line, and the second selection transistor is turned off under the control of the fourth control signal line; The transmission switch and the reset transistor are turned on under the control of the second control signal line and the third control signal line, respectively, to reset the photodiode. After that, the transmission switch and the reset transistor are turned off under the control of the second control signal line and the third control signal line, respectively. After a fifth preset time, the control terminal of the first source follower transistor is reset, and the reset transistor is turned off under the control of the third control signal line to obtain the third reset voltage output by the second selection transistor. The first selection transistor is turned off under the control of the first control signal line, and the second selection transistor is turned on under the control of the fourth control signal line. After a sixth preset time when the transmission switch is turned on, the transmission switch is turned off under the control of the second control signal line to obtain the third signal voltage output by the second selection transistor. The difference between the third reset voltage and the third signal voltage is used as the compensated conversion voltage, and the compensated conversion voltage is output.

7. The pixel signal compensation circuit according to claim 4, characterized in that, Switch the switching unit to one of the first current source and the second current source; turn on the first selection transistor under the control of the first control signal line, and turn off the second selection transistor under the control of the fourth control signal line; The transmission switch and the reset transistor are turned on under the control of the second control signal line and the third control signal line, respectively, so that after the photodiode is reset, the transmission switch and the reset transistor are turned off under the control of the second control signal line and the third control signal line, respectively. After a seventh preset time, the control terminal of the first source follower transistor is reset, and the reset transistor is turned off under the control of the third control signal line to obtain the fourth reset voltage output by the first selection transistor. Switch the switching unit to the other of the first current source and the second current source. After the transmission switch is turned on for an eighth preset time under the control of the second control signal line, turn the transmission switch off under the control of the second control signal line to obtain the fourth signal voltage output by the first selection transistor. The difference between the fourth reset voltage and the fourth signal voltage is used as the compensated conversion voltage, and the compensated conversion voltage is output.

8. The pixel signal compensation circuit according to claim 2, characterized in that, The voltage range of the compensation signal is 0 to 200 mV.

9. The pixel signal compensation circuit according to claim 4, characterized in that, The threshold voltage difference between the first source follower transistor and the second source follower transistor is 100-200mV.

10. An image sensor, characterized in that, include: The pixel signal compensation circuit as described in any one of claims 1-9.

11. An electronic device, characterized in that, include: The image sensor as described in claim 10 above.

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