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CN-122002147-A - Pixel circuit and image sensor

CN122002147ACN 122002147 ACN122002147 ACN 122002147ACN-122002147-A

Abstract

The invention discloses a pixel circuit and an image sensor, relates to the technical field of pixel circuits, and is used for realizing flexible switching of different gains of the pixel circuit. The pixel circuit comprises an input end of a feedback sub-circuit, an amplifying sub-circuit and a gain switching sub-circuit, wherein the input end of the feedback sub-circuit is suitable for being connected with a sensing diode, the feedback sub-circuit is configured to receive and store exposure current output by the sensing diode, the input end of the amplifying sub-circuit is suitable for being connected with the sensing diode, the amplifying sub-circuit is configured to amplify voltage of the input end of the amplifying sub-circuit based on the exposure current output by the sensing diode, the voltage of the sensing diode is clamped at a preset potential through the feedback sub-circuit, the gain switching sub-circuit is connected between a second end of a fourth capacitor and a grounding end, and between the second end of the fourth capacitor and an output end of the amplifying sub-circuit, and the gain switching sub-circuit is configured to control capacitance values between the input end and the output end of the feedback sub-circuit to change gains of the exposure current.

Inventors

  • HUANG FUJUN
  • LI ZHIQIAN

Assignees

  • 天津希格玛微电子技术有限公司

Dates

Publication Date
20260508
Application Date
20260410

Claims (10)

  1. 1. A pixel circuit is characterized by comprising a feedback sub-circuit, an amplifying sub-circuit and a gain switching sub-circuit; The feedback sub-circuit comprises a first capacitor, a second capacitor, a third capacitor and a fourth capacitor, wherein the first end of the first capacitor is suitable for being connected with the light sensing diode, the second end of the first capacitor, the first end of the second capacitor, the first end of the third capacitor and the first end of the fourth capacitor are connected, the second end of the second capacitor is connected with the output end of the amplifying sub-circuit, the second end of the third capacitor is connected with a first voltage end, and the second end of the fourth capacitor is connected with a ground end; The input end of the amplifying sub-circuit is suitable for being connected with the light sensing diode, and the amplifying sub-circuit is configured to amplify the voltage of the input end of the amplifying sub-circuit based on the exposure current output by the light sensing diode; The gain switching sub-circuit is connected between the second end of the fourth capacitor and the ground terminal, and between the second end of the fourth capacitor and the output terminal of the amplifying sub-circuit, and is configured to control a capacitance value between the input terminal and the output terminal of the feedback sub-circuit to change so as to change the gain of the feedback sub-circuit to the exposure current.
  2. 2. The pixel circuit of claim 1, wherein the gain switching sub-circuit comprises a first gain switching switch and a second gain switching switch; The first end of the first gain change-over switch is connected with the second end of the fourth capacitor, and the second end of the first gain change-over switch is connected with the grounding end; the first end of the second gain change-over switch is connected with the second end of the fourth capacitor, and the second end of the second gain change-over switch is connected with the output end of the amplifying sub-circuit; The gain switching subcircuit is configured to: when the first gain change-over switch is in a closed state and the second gain change-over switch is in an open state, the pixel circuit works in a first gain mode; When the second gain change-over switch is in a closed state and the first gain change-over switch is in an open state, the pixel circuit works in a second gain mode; The gain of the amplifying sub-circuit to the exposure current in the first gain mode is larger than that of the amplifying sub-circuit to the exposure current in the second gain mode.
  3. 3. The pixel circuit according to claim 2, wherein, In the first gain mode, the voltage provided by the first voltage end is a grounding voltage before the light sensing diode is exposed, and the grounding voltage is increased to a first preset reference voltage during the light sensing diode is exposed; In the second gain mode, the voltage provided by the first voltage end is a grounding voltage before the light sensing diode is exposed, and the grounding voltage is increased to a second preset reference voltage during the light sensing diode is exposed; Wherein the first preset reference voltage is smaller than the second preset reference voltage.
  4. 4. A pixel circuit according to any one of claims 1-3, wherein the first capacitor has a first capacitance, the second capacitor has a second capacitance, the third capacitor has a third capacitance, and the fourth capacitor has a fourth capacitance; Any one of the first capacity value, the second capacity value and the third capacity value is smaller than the fourth capacity value.
  5. 5. The pixel circuit of claim 4, wherein the first capacitance, the second capacitance, and the third capacitance are the same predetermined capacitance, and the fourth capacitance is N times the predetermined capacitance, N being greater than or equal to 2.
  6. 6. A pixel circuit according to any one of claims 1-3, wherein the pixel circuit further comprises: a first switch coupled between the photodiode and the output terminal of the amplifying sub-circuit; The first switch is configured to be in a closed state between a first time point and a second time point, wherein the first time point is the starting moment of the operation of the pixel circuit, and the second time point is after the first time point, so as to reset the voltage of the output end of the amplifying sub-circuit and the voltage of the light-sensing diode.
  7. 7. The pixel circuit of claim 6, wherein the pixel circuit further comprises: A reset sampling capacitor, a first end of which is coupled to the output end of the amplifying sub-circuit, and a second end of which is coupled to the ground end; The second switch is coupled between the first end of the reset sampling capacitor and the output end of the amplifying sub-circuit, and is configured to be in a closed state between the first time point and a third time point so as to reset the reset sampling capacitor; An exposure sampling capacitor, a first end of which is coupled to the output end of the amplifying sub-circuit, and a second end of which is coupled to the ground end; The third switch is coupled between the first end of the exposure sampling capacitor and the output end of the amplifying sub-circuit, and is configured to be in a closed state between the first time point and a fourth time point so as to reset the exposure sampling capacitor; the third time point is after the second time point and before the light sensing diode starts to expose, and the fourth time point is after the light sensing diode ends to expose.
  8. 8. The pixel circuit of claim 7, wherein, In the first gain mode, after the fourth time point, the voltage provided by the first voltage terminal is reduced from a first preset reference voltage to a ground voltage; in the second gain mode, after the fourth time point, the voltage provided by the first voltage end is reduced from a second preset reference voltage to a ground voltage, wherein the first preset reference voltage is smaller than the second preset reference voltage.
  9. 9. The pixel circuit according to claim 7 or 8, wherein the pixel circuit further comprises: A fourth switch having a first end connected to the first end of the reset sampling capacitor and a second end connected to the first end of the exposure sampling capacitor, the fourth switch being configured to be in an off state when a row selection signal is enabled and a column selection signal is not enabled so that the first end of the reset sampling capacitor is not connected to the first end of the exposure sampling capacitor; The first readout sub-circuit is coupled between the first end and the negative output end of the reset sampling capacitor, and is configured to output a first negative output voltage based on the reset voltage when the fourth switch is in an open state; The second readout sub-circuit is coupled between the first end of the exposure sampling capacitor and the positive output end, and is configured to output a first positive output voltage based on the exposure voltage when the fourth switch is in an open state, and output a second positive output voltage based on the reset voltage and the exposure voltage when the fourth switch is in a closed state.
  10. 10. An image sensor comprising an array of pixels, at least one pixel in the array of pixels comprising a photodiode, and a pixel circuit as claimed in any one of claims 1 to 9.

Description

Pixel circuit and image sensor Technical Field The present invention relates to the field of pixel circuits, and more particularly, to a pixel circuit and an image sensor. Background In the design of pixel circuits of image sensors, the core requirement is to effectively receive, store and amplify the exposure current output by the light-sensing diode so as to ensure the imaging quality. The image sensor includes a plurality of pixel circuits, the performance of each of which together determine the sharpness, uniformity and dynamic range of the final image. The gain of a conventional pixel circuit (such as a 3T pixel circuit, i.e., a pixel circuit including three transistors) is determined by the capacitance value of its internal capacitor, which makes it difficult to flexibly adjust the gain of exposure current according to illumination intensity or noise environment, and thus it is impossible to switch between high-sensitivity and low-noise imaging modes, and applicability in complex illumination scenes is limited. Disclosure of Invention The invention aims to provide a pixel circuit and an image sensor, which are used for realizing flexible switching of different gains of the pixel circuit and meeting imaging gain requirements in different scenes. In order to achieve the above purpose, the embodiment of the invention provides the following technical scheme: In a first aspect, the present invention provides a pixel circuit comprising a feedback sub-circuit, an amplification sub-circuit, and a gain switching sub-circuit. The feedback sub-circuit is configured to receive and store an exposure current output by the light-sensing diode, and comprises a first capacitor, a second capacitor, a third capacitor and a fourth capacitor, wherein the first end of the first capacitor is suitable for being connected with the light-sensing diode, the second end of the first capacitor, the first end of the second capacitor, the first end of the third capacitor and the first end of the fourth capacitor are connected, the second end of the second capacitor is connected with the output end of the amplifying sub-circuit, the second end of the third capacitor is connected with the first voltage end, and the second end of the fourth capacitor is connected with the ground end. The input end of the amplifying sub-circuit is suitable for being connected with the sensing diode, and the amplifying sub-circuit is configured to amplify the voltage of the input end of the amplifying sub-circuit based on the exposure current output by the sensing diode and clamp the voltage of the sensing diode at a preset potential through the feedback sub-circuit. The gain switching sub-circuit is connected between the second end of the fourth capacitor and the ground, and between the second end of the fourth capacitor and the output end of the amplifying sub-circuit, and is configured to control the capacitance value between the input end and the output end of the feedback sub-circuit to change so as to change the gain of the feedback sub-circuit to the exposure current. The invention can effectively control the capacitance value between the input end and the output end of the feedback sub-circuit by introducing the feedback sub-circuit formed by the first capacitor to the fourth capacitor and combining the gain switching sub-circuit. The gain switching sub-circuit is connected between the second end of the fourth capacitor and the grounding end, and between the second end of the fourth capacitor and the output end of the amplifying sub-circuit, and the connection state of the gain switching sub-circuit is switched, so that the connection mode of the fourth capacitor in the circuit can be changed, the equivalent capacitance of the feedback sub-circuit can be flexibly adjusted, the adjustment of the gain of exposure current can be further realized, and the pixel circuit can adapt to different exposure condition requirements. In some embodiments, the gain switching sub-circuit comprises a first gain switching switch and a second gain switching switch, wherein a first end of the first gain switching switch is connected with a second end of the fourth capacitor, a second end of the first gain switching switch is connected with a ground end, a first end of the second gain switching switch is connected with a second end of the fourth capacitor, and a second end of the second gain switching switch is connected with an output end of the amplifying sub-circuit. The gain switching sub-circuit is configured to operate in a first gain mode when the first gain switching switch is in a closed state and the second gain switching switch is in an open state, and operate in a second gain mode when the second gain switching switch is in a closed state and the first gain switching switch is in an open state, wherein the gain of the amplifying sub-circuit to the exposure current in the first gain mode is greater than the gain of the amplifying sub-circuit to the exposure