Pixel circuit, image sensor, and imaging device

Abstract

The application discloses a pixel circuit, an image sensor and a shooting device. The pixel circuit comprises a charge generation module, a non-linear module and a reading module. The charge generation module is configured to convert a light signal into an electric signal. The non-linear module is connected with the charge generation module. The non-linear module comprises a sub-threshold transistor and a threshold compensation unit. The sub-threshold transistor is configured to perform non-linear mapping on the electric signal generated by the charge generation module, to generate a non-linear electric signal corresponding to the electric signal generated by the charge generation module. The threshold compensation unit is configured to perform threshold compensation on the sub-threshold transistor. The reading module is connected with the charge generation module and the non-linear module, and is configured to output a pixel signal according to the electric signal of the charge generation module or the non-linear electric signal generated by the non-linear module.

Description

Technical Field

[0001] This utility model relates to the field of image acquisition, and in particular to a pixel circuit, an image sensor, and an imaging device. Background Technology

[0002] Complementary metal-oxide-semiconductor (CMOS) image sensors have been practically used in imaging devices employing photoelectric conversion elements. These photoelectric conversion elements detect light and generate electrical charges. They are widely used in portable terminal devices such as digital cameras, camcorders, surveillance cameras, medical endoscopes, personal computers, automotive cameras, and mobile phones.

[0003] Nonlinear image sensors, as one of the technological directions for improving dynamic range, have promising application prospects. However, among related technologies, nonlinear image sensors have high FPN (Fixed Pattern Noise), which limits the development of this technological approach. Utility Model Content

[0004] The purpose of this application is to provide a pixel circuit, an image sensor, and an imaging device with low output noise.

[0005] This application discloses a pixel circuit, the pixel circuit comprising:

[0006] The charge generation module is configured to convert optical signals into electrical signals;

[0007] A nonlinear module is connected to the charge generation module. The nonlinear module includes a subthreshold transistor and a threshold compensation unit. The subthreshold transistor is configured to perform nonlinear mapping on the electrical signal generated by the charge generation module to generate a nonlinear electrical signal corresponding to the electrical signal generated by the charge generation module. The threshold compensation unit is configured to perform threshold compensation on the subthreshold transistor.

[0008] The reading module, connected to the charge generation module and the nonlinear module, is configured to output a pixel signal based on the electrical signal from the charge generation module or the nonlinear electrical signal generated by the nonlinear module.

[0009] Optionally, the pixel circuit further includes a second reference signal terminal;

[0010] The control electrode and the first electrode of the subthreshold transistor are both connected to the second reference signal terminal, and the second electrode of the subthreshold transistor is connected to the charge generation module.

[0011] Optionally, the pixel circuit further includes a first reference signal terminal, a fifth control signal terminal, a sixth control signal terminal, and a seventh control signal terminal;

[0012] The threshold compensation unit includes:

[0013] The fifth transistor has its first terminal connected to the fourth node, its second terminal connected to the third node, and its control terminal connected to the fifth control signal terminal.

[0014] The sixth transistor has its first terminal connected to the first reference signal terminal, its second terminal connected to the fourth node, and its control terminal connected to the sixth control signal terminal.

[0015] The seventh transistor has its first terminal connected to the second reference signal terminal, its second terminal connected to the fifth node, and its control terminal connected to the seventh control signal terminal.

[0016] A capacitor, wherein the first terminal of the capacitor is connected to the fourth node, and the second terminal is connected to the fifth node;

[0017] The third node is connected to the charge generation module and the second electrode of the subthreshold transistor, and the fifth node is connected to the control electrode of the subthreshold transistor.

[0018] Optionally, the pixel circuit further includes a fourth control signal terminal;

[0019] The nonlinear module further includes:

[0020] The fourth transistor has its first terminal connected to the third node, its second terminal connected to the second node, and its control terminal connected to the fourth control signal terminal.

[0021] The second node is connected to the charge generation module.

[0022] Optionally, the pixel circuit further includes a reset module and a first power signal terminal; the reset module is connected to the charge generation module and is configured to reset the charge generation module;

[0023] The reset module includes:

[0024] The tenth transistor has its first terminal connected to the first power signal terminal, its second terminal connected to the second node, and its control terminal connected to the reset signal terminal.

[0025] The second node is connected to the charge generation module.

[0026] Optionally, the pixel circuit further includes a second transistor and a second control signal terminal;

[0027] The first terminal of the second transistor is connected to the second node, the second terminal is connected to the first node, and the control terminal is connected to the second control signal terminal;

[0028] The first node is connected to the charge generation module and the reading module.

[0029] Optionally, the pixel circuit further includes a first control signal terminal and a second power supply signal terminal;

[0030] The charge generation module includes:

[0031] A photodiode, wherein the first terminal of the photodiode is connected to the second power signal terminal, and the second terminal is connected to the first terminal of the first transistor;

[0032] The second terminal of the first transistor is connected to the first node, and the control terminal is connected to the first control signal terminal.

[0033] The first node is connected to the nonlinear module and the reading module.

[0034] Optionally, the pixel circuit further includes a third control signal terminal, a first power supply signal terminal, and an output signal terminal;

[0035] The reading module includes:

[0036] The eighth transistor has its first terminal connected to the first power signal terminal, its second terminal connected to the first terminal of the ninth transistor, and its control terminal connected to the first node.

[0037] The second terminal of the ninth transistor is connected to the output signal terminal, and the control terminal is connected to the third control signal terminal;

[0038] The first node is connected to the charge generation module and the nonlinear module.

[0039] This application also discloses an image sensor, which includes the pixel circuit described above.

[0040] This application also discloses a shooting device, which includes the image sensor described above.

[0041] Compared with related technologies, this application sets up a nonlinear module, which includes a subthreshold transistor and a threshold compensation unit. The threshold compensation unit performs threshold compensation on the subthreshold transistor, eliminating the adverse effects caused by the different threshold voltages of different subthreshold transistors and reducing the noise of the image sensor.

[0042] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this specification. Attached Figure Description

[0043] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this specification and, together with the description, serve to explain the principles of this specification.

[0044] Figure 1 This is a schematic diagram of the pixel circuit module of this application.

[0045] Figure 2 As one embodiment Figure 1 The circuit diagram of the module is shown in the figure.

[0046] Figure 3 As one embodiment Figure 2 Timing diagram of the circuit. Detailed Implementation

[0047] The technical solutions in the embodiments (or "implementations") of this application will be clearly and completely described herein with reference to the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements.

[0048] If the embodiments of this application contain terms relating to directional indications or positional relationships (such as up, down, left, right, front, back, inside, outside, top, bottom, center, vertical, horizontal, longitudinal, transverse, length, width, counterclockwise, clockwise, axial, radial, circumferential, etc.), such terms are only used to explain the relative positional relationships and movements between components in a specific posture (as shown in the attached figures); if the specific posture changes, the directional indications or positional relationships will also change accordingly. Furthermore, the terms "first" and "second" used in the embodiments of this application are only for descriptive convenience and should not be construed as indicating or implying relative importance.

[0049] Nonlinear image sensors, as one of the technological directions for improving dynamic range, have promising application prospects. However, among related technologies, nonlinear image sensors have relatively high FPN (Fixed Pattern Noise). The inventors discovered through research that the different threshold voltages of different subthreshold transistors have a significant impact on the noise of the image sensor.

[0050] To this end, this application provides a pixel circuit, which includes a charge generation module 10, a nonlinear module 20, and a readout module 30.

[0051] The charge generation module 10 is configured to convert optical signals into electrical signals. A nonlinear module 20 is connected to the charge generation module 10. The nonlinear module 20 includes a subthreshold transistor T3 and a threshold compensation unit. The subthreshold transistor T3 is configured to perform nonlinear mapping on the electrical signal generated by the charge generation module 10, generating a nonlinear electrical signal corresponding to the electrical signal generated by the charge generation module 10. The threshold compensation unit is configured to perform threshold compensation on the subthreshold transistor T3. A readout module 30 is connected to the charge generation module 10 and the nonlinear module 20, and is configured to output pixel signals based on the electrical signals from the charge generation module 10 or the nonlinear electrical signals generated by the nonlinear module 20.

[0052] This application incorporates a nonlinear module, which includes a subthreshold transistor and a threshold compensation unit. The threshold compensation unit performs threshold compensation on the subthreshold transistor, eliminating the adverse effects caused by the different threshold voltages of different subthreshold transistors and reducing the noise of the image sensor.

[0053] The following will provide a detailed description of various embodiments of this application that conform to the above-described inventive concept.

[0054] like Figure 1 as well as Figure 2 As shown in the figure, this application discloses a pixel circuit, which includes a charge generation module 10, a nonlinear module 20, and a readout module 30.

[0055] The charge generation module 10 and the nonlinear module 20 are both connected to the readout module 30. Optionally, the pixel circuit may further include a reset module 40, which is connected to the charge generation module 10 and configured to reset the charge generation module 10.

[0056] The pixel circuit of this application may include a first power supply signal terminal VDD, a second power supply signal terminal VSS, a first reference signal terminal VREF1, a second reference signal terminal VREF2, a reset signal terminal RST, an output signal terminal OUT, and first control signal terminals S1 to seventh control signal terminals S7. The first power supply signal terminal VDD is configured to provide a first power supply signal vdd, which is a constant high-level signal. The second power supply signal terminal VSS is configured to provide a second power supply signal vss, which is a constant low-level signal. The first reference signal terminal VREF1 is configured to provide a first reference signal vref1, and the second reference signal terminal VREF2 is configured to provide a second reference signal vref2. The reset signal terminal RST is configured to provide a reset signal rst. The output signal terminal OUT is used to output the pixel signal. The first control signal terminals S1 to the seventh control signal terminals S7 are respectively configured to provide first control signals s1 to seventh control signals s7. In this embodiment, all transistors are N-type transistors as an example. In actual circuits, the transistor types can be adjusted according to requirements.

[0057] The charge generation module 10 may include a photodiode PD and a first transistor T1. The first terminal of the photodiode PD is connected to the second power signal terminal VSS, and the second terminal of the photodiode PD is connected to the first terminal of the first transistor T1. The second terminal of the first transistor T1 is connected to the first node N1, and the control terminal of the first transistor T1 is connected to the first control signal terminal S1.

[0058] The nonlinear module 20 may include a subthreshold transistor T3 and a threshold compensation unit. The control electrode and first electrode of the subthreshold transistor T3 are both connected to the second reference signal terminal VREF2, and the second electrode of the subthreshold transistor T3 is connected to the charge generation module 10. The subthreshold transistor T3 operates in the subthreshold region to achieve nonlinear mapping of the electrical signal generated by the charge generation module 10. The threshold compensation unit may include a fifth transistor T5, a sixth transistor T6, a seventh transistor T7, and a capacitor C1. The first electrode of the fifth transistor T5 is connected to the fourth node N4, the second electrode of the fifth transistor T5 is connected to the third node N3, and the control electrode of the fifth transistor T5 is connected to the fifth control signal terminal S5. The first electrode of the sixth transistor T6 is connected to the first reference signal terminal VREF1, the second electrode of the sixth transistor T6 is connected to the fourth node N4, and the control electrode of the sixth transistor T6 is connected to the sixth control signal terminal S6. The first electrode of the seventh transistor T7 is connected to the second reference signal terminal VRFE2, the second electrode is connected to the fifth node N5, and the control electrode is connected to the seventh control signal terminal S7. The first terminal of capacitor C1 is connected to the fourth node N4, and the second terminal is connected to the fifth node N5. Optionally, the nonlinear module 20 may further include a fourth transistor T4, the first terminal of which is connected to the third node N3, the second terminal of which is connected to the second node N2, and the control terminal of which is connected to the fourth control signal terminal S4.

[0059] The reading module 30 may include an eighth transistor T8 and a ninth transistor T9. The first terminal of the eighth transistor T8 is connected to the first power supply signal terminal VDD, the second terminal of the eighth transistor T8 is connected to the first terminal of the ninth transistor T9, and the control terminal of the eighth transistor T8 is connected to the first node N1. The second terminal of the ninth transistor T9 is connected to the output signal terminal OUT, and the control terminal of the ninth transistor T9 is connected to the third control signal terminal S3.

[0060] The reset module 40 may include a tenth transistor T10. The first terminal of the tenth transistor T10 is connected to the first power supply signal terminal VDD, the second terminal of the tenth transistor T10 is connected to the second node N2, and the control terminal of the tenth transistor T10 is connected to the reset signal terminal RST.

[0061] The pixel circuit may also include a second transistor T2, the first terminal of which is connected to the second node N2, the second terminal of which is connected to the first node N1, and the control terminal of which is connected to the second control signal terminal S2.

[0062] like Figure 3 As shown, Figure 3 As one embodiment Figure 2 The timing diagram of the pixel circuit is shown.

[0063] During period H1, transistors T1, T2, and T10 are turned on, while transistors T9 and T4 are turned off. The first power supply signal vdd resets the well of the photodiode PD. Simultaneously, transistors T5, T6, and T7 are turned on, and the first reference signal vref1 and the second reference signal vref2 are at low potentials, thus resetting capacitor C1.

[0064] During period H2, transistors T1, T6, and T10 are turned off, while the other transistors are turned on. Simultaneously, the first reference signal vref1 and the second reference signal vref2 go high. Transistor T3 operates in diode mode, and the voltage difference between the two terminals of capacitor C1 is Vth (the threshold voltage of transistor T3), where the second terminal of capacitor C1 is Vth higher than the first terminal. At the same time, the readout module 30 outputs the first pixel signal.

[0065] During period H3, transistors T5, T7, and T10 are off, while the other transistors are on. The second terminal of capacitor C1, i.e., the gate of transistor T3, is coupled to vref1+Vth.

[0066] When the circuit is in a steady state:

[0067]

[0068] Where a and k are constants, Vg and Vs are the gate and source voltages of the third transistor T3, respectively, and Iph is the electrical signal generated by the charge generation module 10. DS Vth is the drain current of the third transistor T3, and Vth is the threshold voltage of the third transistor T3.

[0069] Taking the natural logarithm from both sides of equation ① and rearranging, we get:

[0070]

[0071] Since the gate of the third transistor T3 is coupled to vref1+Vth, substituting into equation ② yields...

[0072]

[0073] From equation ③, it can be seen that the source voltage Vs of the third transistor T3 has a nonlinear relationship with the electrical signal Iph generated by the charge generation module 10, and the threshold voltage of the third transistor T3 has been compensated, so its source voltage Vs is independent of its threshold voltage Vth.

[0074] The reading module 30 reads the second pixel signal based on Vs. The second pixel signal is a photoelectric signal with a high dynamic range. The first pixel signal can then be used to reduce noise in the second pixel signal.

[0075] This application incorporates a nonlinear module including subthreshold transistors and a threshold compensation unit. The threshold compensation unit consists of only a few transistors and a capacitor. This allows for threshold compensation of the subthreshold transistors without significantly increasing the pixel circuit area, eliminating the adverse effects caused by the different threshold voltages of different subthreshold transistors and reducing the noise of the image sensor.

[0076] This application also discloses an image sensor, which includes the pixel circuit described above.

[0077] This application also discloses an imaging device, which includes the image sensor described above.

[0078] The shooting device can be a mobile phone, camera, wearable device, vehicle-mounted device, etc.

[0079] It should be noted that the technical solutions or features described in the above embodiments can be combined or supplemented with each other without conflict. The scope of protection of this application is not limited to the precise structures described in the above embodiments and shown in the accompanying drawings; all modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A pixel circuit, characterized in that, The pixel circuit includes: The charge generation module is configured to convert optical signals into electrical signals; A nonlinear module is connected to the charge generation module. The nonlinear module includes a subthreshold transistor and a threshold compensation unit. The subthreshold transistor is configured to perform nonlinear mapping on the electrical signal generated by the charge generation module to generate a nonlinear electrical signal corresponding to the electrical signal generated by the charge generation module. The threshold compensation unit is configured to perform threshold compensation on the subthreshold transistor. The reading module, connected to the charge generation module and the nonlinear module, is configured to output a pixel signal based on the electrical signal from the charge generation module or the nonlinear electrical signal generated by the nonlinear module.

2. The pixel circuit according to claim 1, characterized in that, The pixel circuit also includes a second reference signal terminal; The control electrode and the first electrode of the subthreshold transistor are both connected to the second reference signal terminal, and the second electrode of the subthreshold transistor is connected to the charge generation module.

3. The pixel circuit according to claim 2, characterized in that, The pixel circuit further includes a first reference signal terminal, a fifth control signal terminal, a sixth control signal terminal, and a seventh control signal terminal; The threshold compensation unit includes: The fifth transistor has its first terminal connected to the fourth node, its second terminal connected to the third node, and its control terminal connected to the fifth control signal terminal. The sixth transistor has its first terminal connected to the first reference signal terminal, its second terminal connected to the fourth node, and its control terminal connected to the sixth control signal terminal. The seventh transistor has its first terminal connected to the second reference signal terminal, its second terminal connected to the fifth node, and its control terminal connected to the seventh control signal terminal. A capacitor, wherein the first terminal of the capacitor is connected to the fourth node, and the second terminal is connected to the fifth node; The third node is connected to the charge generation module and the second electrode of the subthreshold transistor, and the fifth node is connected to the control electrode of the subthreshold transistor.

4. The pixel circuit according to claim 3, characterized in that, The pixel circuit also includes a fourth control signal terminal; The nonlinear module further includes: The fourth transistor has its first terminal connected to the third node, its second terminal connected to the second node, and its control terminal connected to the fourth control signal terminal. The second node is connected to the charge generation module.

5. The pixel circuit according to claim 1, characterized in that, The pixel circuit also includes a reset module and a first power signal terminal; the reset module is connected to the charge generation module and is configured to reset the charge generation module; The reset module includes: The tenth transistor has its first terminal connected to the first power supply signal terminal, its second terminal connected to the second node, and its control terminal connected to the reset signal terminal. The second node is connected to the charge generation module.

6. The pixel circuit according to claim 5, characterized in that, The pixel circuit also includes a second transistor and a second control signal terminal; The first terminal of the second transistor is connected to the second node, the second terminal is connected to the first node, and the control terminal is connected to the second control signal terminal; The first node is connected to the charge generation module and the reading module.

7. The pixel circuit according to claim 1, characterized in that, The pixel circuit also includes a first control signal terminal and a second power signal terminal; The charge generation module includes: A photodiode, wherein the first terminal of the photodiode is connected to the second power signal terminal, and the second terminal is connected to the first terminal of the first transistor; The second terminal of the first transistor is connected to the first node, and the control terminal is connected to the first control signal terminal. The first node is connected to the nonlinear module and the reading module.

8. The pixel circuit according to claim 1, characterized in that, The pixel circuit also includes a third control signal terminal, a first power signal terminal, and an output signal terminal; The reading module includes: The eighth transistor has its first terminal connected to the first power signal terminal, its second terminal connected to the first terminal of the ninth transistor, and its control terminal connected to the first node. The second terminal of the ninth transistor is connected to the output signal terminal, and the control terminal is connected to the third control signal terminal; The first node is connected to the charge generation module and the nonlinear module.

9. An image sensor, characterized in that, The image sensor includes the pixel circuitry as described in any one of claims 1-8.

10. A shooting device, characterized in that, The imaging device includes the image sensor as described in claim 9.

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