Light sensing circuit, chip and electronic device

Abstract

The application provides a light sensing circuit, a chip and an electronic device. An input end of a clamping circuit is connected to a cathode of a photodiode, and an output end of the clamping circuit is connected to an input end of an amplifier circuit. The photodiode and the amplifier circuit are isolated by using the clamping circuit. The clamping circuit can clamp the cathode voltage of the photodiode to a target voltage, maintain the zero bias state of the photodiode, avoid affecting the photoelectric current characteristic of the photodiode, and still keep the input current flowing into the amplifier circuit equal to the photoelectric current of the photodiode, that is, the size of the photoelectric current extracted from the integrating capacitor is not changed, and the amplifier circuit does not affect the normal amplification of the photoelectric current. Therefore, the linearity of photoelectric conversion can be improved, and the precision of light detection can be improved.

Description

Technical Field

[0001] This application relates to photoelectric conversion technology, and more particularly to a photosensitive circuit, chip, and electronic device. Background Technology

[0002] A light-sensing circuit uses a light-sensing element to convert an input light signal into an electrical signal output, thus enabling light detection. Common light-sensing circuits use photodiodes to sense light and amplifiers to amplify the photocurrent output by the photodiode.

[0003] However, the cathode of a photodiode is usually directly connected to the input of an amplifier. There is a coupling relationship between the cathode voltage of the photodiode and the output voltage of the amplifier. Due to the virtual short characteristic of operational amplifiers, the photodiode may be slightly forward biased. In this case, the photoelectric conversion efficiency of the photodiode will deviate from that at zero bias, affecting the linear relationship between its photocurrent and the detected light intensity. Summary of the Invention

[0004] This application provides a photosensitive circuit, chip, and electronic device for maintaining a photodiode in a zero-bias state and improving the linearity of photoelectric conversion.

[0005] In a first aspect, embodiments of this application provide a photosensitive circuit, including: a photodiode, an amplifier circuit, and a clamping circuit;

[0006] The output terminal of the clamping circuit is connected to the input terminal of the amplifier circuit, the input terminal of the clamping circuit is connected to the cathode of the photodiode, and the anode of the photodiode is grounded.

[0007] The clamping circuit is used to clamp the cathode voltage of the photodiode to the target voltage and to transfer the photocurrent generated by the photodiode to the input terminal of the amplifier circuit.

[0008] Optionally, the clamping circuit includes: a feedback module and a voltage clamping module;

[0009] The input terminal of the feedback module serves as the input terminal of the clamping circuit, and the output terminal of the feedback module serves as the output terminal of the clamping circuit. It is used to output clamping current according to the cathode voltage of the photodiode and to transmit the photocurrent generated by the photodiode to the input terminal of the amplifier circuit.

[0010] The first end of the voltage clamping module is connected to the input end of the feedback module, and the second end of the voltage clamping module is connected to the anode of the photodiode, for stabilizing the cathode voltage of the photodiode at the target voltage based on the clamping current.

[0011] Optionally, the voltage clamping module includes: a clamping resistor;

[0012] The first end of the clamping resistor serves as the first end of the voltage clamping module, and the second end of the clamping resistor serves as the second end of the voltage clamping module.

[0013] Optionally, the feedback module includes: an operational amplifier and a transistor;

[0014] The non-inverting input of the operational amplifier receives a reference voltage, the inverting input of the operational amplifier serves as the input of the feedback module, and the output of the operational amplifier is connected to the gate of the transistor.

[0015] The drain of the transistor serves as the output terminal of the feedback module, and the source of the transistor is connected to the inverting input terminal of the operational amplifier.

[0016] Wherein, the magnitude of the reference voltage is equal to the target voltage;

[0017] The transistor is used to transfer the photocurrent generated by the photodiode from its source to its drain so that it flows into the input terminal of the amplifier circuit.

[0018] Optionally, the feedback module further includes:

[0019] A current source, connected to the drain of the transistor, is used to provide bias current to the transistor in order to provide clamping current to the voltage clamping module.

[0020] Optionally, when the transistor is operating in saturation, the square of the difference between the output voltage of the operational amplifier and the threshold voltage of the transistor is proportional to the magnitude of the clamping current.

[0021] And / or, the difference between the reference voltage and the cathode voltage clamp of the photodiode is proportional to the output voltage of the operational amplifier.

[0022] Optionally, the amplifier circuit includes: a capacitor feedback transimpedance amplifier, an integrating capacitor, and a reset switch;

[0023] The inverting input terminal of the capacitor feedback transimpedance amplifier serves as the input terminal of the amplifier circuit and is connected to the output terminal of the clamping circuit.

[0024] Both the integrating capacitor and the reset switch are connected across the inverting input and output of the capacitor feedback transimpedance amplifier.

[0025] Optionally, the output voltage of the capacitor feedback transimpedance amplifier is equal to the sum of the common-mode voltage and the integral voltage increment of the capacitor feedback transimpedance amplifier; the integral voltage increment is equal to the ratio of the integral value of the photocurrent generated by the photodiode during the integration time to the capacitance value of the integrating capacitor.

[0026] Secondly, embodiments of this application provide a chip including the photosensitive circuit described in the first aspect.

[0027] Thirdly, this application provides an electronic device including the chip described in the second aspect.

[0028] The photosensitive circuit, chip, and electronic device provided in this application have a clamping circuit whose input terminal is connected to the cathode of a photodiode, and whose output terminal is connected to the input terminal of an amplifier circuit. The clamping circuit isolates the photodiode and the amplifier circuit. The clamping circuit can clamp the cathode voltage of the photodiode to the target voltage, maintain the photodiode in a zero-bias state, and avoid affecting the photocurrent characteristics of the photodiode. At the same time, the input current flowing into the amplifier circuit is still equal to the photocurrent of the photodiode, that is, it does not change the photocurrent of the condenser capacitor, and does not affect the normal amplification of the photocurrent by the amplifier circuit. This can improve the linearity of photoelectric conversion and improve the accuracy of photodetection. Attached Figure Description

[0029] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0030] Figure 1 This is a schematic diagram of the structure of a photosensitive circuit in an exemplary related technology;

[0031] Figure 2 This is a schematic diagram of the structure of a photosensitive circuit provided in an embodiment of this application.

[0032] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0033] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0034] In this application, a module refers to a functional module or a logical module. It can be in software form, where its function is implemented by a processor executing program code; or it can be in hardware form. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. The character " / " generally indicates that the preceding and following related objects have an "OR" relationship.

[0035] First, some terms used in the embodiments of this application will be explained.

[0036] Zero bias: The voltage difference across the photodiode is zero.

[0037] Reverse bias: The voltage difference between the anode and cathode of a photodiode is negative.

[0038] A light-sensing circuit uses a light-sensing element to convert an input light signal into an electrical signal output, thus enabling light detection. Common light-sensing circuits use photodiodes to sense light and amplifiers to amplify the photocurrent output by the photodiode.

[0039] like Figure 1 As shown, the photosensitive circuit includes a photodiode PD, a capacitor feedback transimpedance amplifier CTIA, an integrating capacitor Cint, and a reset switch rst. The anode of the photodiode is grounded, and the cathode is connected to the PD_K terminal, which is also the inverting input VIN of the capacitor feedback transimpedance amplifier. The non-inverting input of the capacitor feedback transimpedance amplifier receives the common-mode voltage VCM. The integrating capacitor is connected across the inverting input and output of the capacitor feedback transimpedance amplifier, serving as a feedback branch. The reset switch is connected in parallel with the integrating capacitor to reset the voltage across the integrating capacitor before integration, clearing the charge from the previous integration.

[0040] During the reset phase: the reset switch is closed, the two ends of the integrating capacitor are shorted, the voltage across the integrating capacitor is cleared to zero, at this time the output voltage VO of the capacitor feedback transimpedance amplifier is equal to the common-mode voltage VCM, and the circuit completes the reset.

[0041] During the integration phase: When the reset switch is open, the photodiode is illuminated and generates a photocurrent Ipd, which flows from the cathode to the anode of the photodiode. Due to the virtual short characteristic of the operational amplifier, the photocurrent cannot flow into the capacitor feedback transimpedance amplifier; instead, it flows entirely through the integrating capacitor, charging it.

[0042] Based on the voltage-current relationship of the capacitor, the output voltage VO can be expressed as:

[0043]

[0044] Where Tint is the integration time, and if the light intensity is constant and the photocurrent Ipd is constant, then the output voltage can be simplified to:

[0045]

[0046] In optical sensing applications, photodiodes typically operate in a zero-bias or reverse-biased state. Figure 1 In the structure shown, the cathode of the photodiode is directly connected to the inverting input of the capacitor feedback transimpedance amplifier. Therefore, the cathode voltage VPD of the photodiode is equal to the inverting input voltage VIN of the capacitor feedback transimpedance amplifier. According to the virtual short characteristic of the operational amplifier, there is the following relationship between the inverting input voltage VIN and the output voltage VO: VPD = VCM - VO / G; where G is the open-loop gain of the amplifier.

[0047] Because the cathode voltage VPD of the photodiode is directly coupled to the output voltage VO of the amplifier, VPD will fluctuate as VO changes with the integration time. Specifically:

[0048] When the photodiode is operating in a zero-bias state (VCM=0), as VO increases, VPD may be greater than 0, causing the photodiode to be slightly forward biased.

[0049] When the photodiode is operating in reverse bias (VCM>0), the bias voltage of the photodiode will also fluctuate with the change of photocurrent.

[0050] Such bias fluctuations can affect the photocurrent characteristics of photodiodes, worsen the linearity of photoelectric conversion, and thus reduce the accuracy of photodetection.

[0051] To address the aforementioned technical problems, this application provides a photosensitive circuit and a photodetector, which clamps the cathode voltage of the photodiode using a clamping module to prevent fluctuations in the cathode voltage of the photodiode from affecting its photocurrent characteristics.

[0052] The technical solutions of this application are illustrated below with specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments.

[0053] Figure 2 This is a schematic diagram of a photosensitive circuit provided in an embodiment of this application. Figure 2 As shown, the photosensitive circuit 10 provided in this application embodiment includes: a photodiode PD, an amplifier circuit 200, and a clamping circuit 100.

[0054] The output terminal of the clamping circuit 100 is connected to the input terminal of the amplifier circuit 200, the input terminal of the clamping circuit 100 is connected to the cathode of the photodiode PD, and the anode of the photodiode PD is grounded.

[0055] Clamping circuit 100 is used to clamp the cathode of photodiode PD to the target voltage and to transfer the photocurrent generated by photodiode PD to the input terminal of amplifier circuit 200.

[0056] For example, during the photosensitive process, the photodiode PD generates a photocurrent, which flows out from the cathode of the photodiode PD and is injected into the input terminal of the amplifier circuit 200 through the clamping circuit 100, charging the integrating capacitor in the amplifier circuit 200, thereby causing a change in the output voltage of the amplifier circuit 200.

[0057] The clamping circuit 100 acts as an isolation device between the input terminal of the amplifier circuit 200 and the cathode of the photodiode PD. This isolation prevents the cathode of the photodiode PD from being directly connected to the input terminal of the amplifier circuit 200, thereby preventing the cathode voltage of the photodiode PD from fluctuating with the output voltage of the amplifier circuit 200.

[0058] On one hand, the clamping circuit 100 clamps the cathode voltage of the photodiode PD to the target voltage, preventing it from being affected by changes in the amplifier output voltage. By maintaining the cathode voltage of the photodiode PD at the target voltage, the photodiode PD can operate in ideal zero-bias, reverse-bias, and other operating states, avoiding the influence of changes in the cathode voltage of the photodiode PD on the photocurrent characteristics of the photodiode PD, ensuring that the photocurrent maintains a linear relationship with the incident light intensity, thereby stabilizing the bias voltage of the photodiode PD and enabling it to generate a stable photocurrent that is linearly related to the incident light intensity.

[0059] On the other hand, while clamping the voltage, the clamping circuit 100 also transfers the photocurrent generated by the photodiode PD to the input terminal of the amplifier circuit 200, making the input current flowing into the amplifier circuit 200 essentially equal to the photocurrent generated by the photodiode PD. This characteristic ensures that the linear photocurrent generated by the photodiode PD is fully received by the amplifier circuit 200 and used to extract (i.e., charge) the integrating capacitor, avoiding signal distortion caused by the shunting or loss of the photocurrent by the clamping circuit 100, and not affecting the normal amplification process of the photocurrent by the amplifier circuit 200.

[0060] Through the synergistic effect of voltage clamping and current transfer, the linear photocurrent generated by the photodiode PD is completely converted into the output voltage of the amplifier circuit 200. This ensures that the output voltage of the amplifier circuit 200 remains proportional to the magnitude of the photocurrent, improving the linearity of the output voltage of the amplifier circuit 200 to the photocurrent. Consequently, the output voltage of the amplifier circuit 200 can accurately reflect the light intensity, effectively improving the accuracy of light detection. The optimization effect is particularly significant in low light intensity or long-term integration scenarios.

[0061] In some embodiments, the clamping circuit 100 includes a feedback module 110 and a voltage clamping module 120;

[0062] The output terminal of the feedback module 110 serves as the output terminal of the clamping circuit 100 and is connected to the input terminal of the amplifier circuit 200. The input terminal of the feedback module 110 serves as the input terminal of the clamping circuit 100 and is connected to the cathode of the photodiode PD. The first terminal of the voltage clamping module 120 is connected to the first terminal of the feedback module 110, and the second terminal of the voltage clamping module 120 is connected to the anode of the photodiode PD. That is, the voltage clamping module 120 is connected in parallel with the photodiode PD.

[0063] Feedback module 110 is used to output clamping current Ic to voltage clamping module 120 based on the cathode voltage of photodiode PD, and to transmit the photocurrent generated by photodiode PD to the input terminal of amplifier circuit 200; voltage clamping module 120 is used to stabilize the cathode voltage of photodiode PD at the target voltage based on clamping current Ic.

[0064] The voltage clamping module 120 is connected in parallel with the photodiode PD. Therefore, by injecting a clamping current Ic into the voltage clamping module 120, the voltage across the voltage clamping module 120 can be controlled, thereby clamping the cathode voltage of the photodiode PD to the target voltage. Simultaneously, the input current flowing into the amplifier circuit 200 remains equal to the photocurrent of the photodiode PD, meaning the photocurrent of the condenser capacitor is not changed, and the normal current amplification by the amplifier circuit 200 is not affected. The feedback module 110 can adjust the clamping current Ic according to the cathode voltage of the photodiode PD. The voltage across the voltage clamping module 120 changes with the clamping current, thereby clamping the cathode voltage of the photodiode PD to the required voltage.

[0065] Through this closed-loop feedback control, the cathode voltage of the photodiode PD remains stable and is not affected by changes in the amplifier output voltage, ensuring that the photocurrent maintains a linear relationship with the incident light intensity. At the same time, the photocurrent is completely transmitted to the input terminal of the amplifier circuit 200, so that the output voltage of the amplifier circuit 200 linearly reflects the incident light intensity, effectively improving the accuracy of light detection.

[0066] It should be noted that the clamping circuit 100, including the feedback module 110 and the voltage clamping module 120, is only one example. The clamping circuit 100 can also include other implementations, such as a single-stage feedback amplifier. The input terminal of this single-stage feedback amplifier is connected to the cathode of the photodiode PD, and the output terminal is connected to the input terminal of the amplifier circuit 200. This single-stage feedback amplifier forms a negative feedback loop to clamp the cathode voltage of the photodiode PD to the target voltage and transfer the photocurrent generated by the photodiode PD to the input terminal of the amplifier circuit 200. This single-stage feedback amplifier can be an operational amplifier, with its non-inverting input terminal connected to the target voltage, its inverting input terminal connected to the cathode of the photodiode PD, and its output terminal connected to the input terminal of the amplifier circuit 200. During operation, the operational amplifier clamps the cathode voltage of the photodiode PD to the reference voltage (i.e., the target voltage) at the non-inverting input terminal through the virtual ground characteristic of its inverting input terminal. At the same time, the photocurrent generated by the photodiode PD flows out from the cathode, flows into the operational amplifier through the inverting input terminal, charges the integrating capacitor in the amplifier circuit 200, and thus transfers the photocurrent to the input terminal of the amplifier circuit 200. Through this negative feedback, the operational amplifier simultaneously achieves voltage clamping and current transfer.

[0067] In one possible implementation, the voltage clamping module 120 includes: a clamping resistor R;

[0068] The first end of the clamping resistor R serves as the first end of the voltage clamping module 120 and is connected to the cathode of the photodiode PD; the second end of the clamping resistor R serves as the second end of the voltage clamping module 120 and is connected to the anode of the photodiode PD.

[0069] The voltage across the clamping resistor R changes linearly with the magnitude of the current flowing through it. Therefore, the photosensitive circuit 10 can control the voltage across the clamping resistor R by controlling the magnitude of the clamping current Ic, thus achieving the purpose of clamping the cathode voltage of the photodiode PD. The clamping resistor R is a passive component, simple in structure, easy to integrate, and inexpensive. Furthermore, the linear relationship between the voltage across the clamping resistor R and the clamping current Ic allows the feedback module 110 to precisely control the cathode voltage of the photodiode PD by linearly adjusting the clamping current Ic.

[0070] For example, in a stable clamping state, the voltage across the clamping resistor R is equal to the target voltage Vc, and the current flowing through the clamping resistor R is the clamping current Ic. According to Ohm's law, in a stable clamping state, Ic = Vc / R is satisfied.

[0071] It should be noted that the voltage clamping module 120 including a clamping resistor is only one example. The voltage clamping module 120 can also include other implementations, such as including a transistor. The control terminal of the transistor is connected to the output terminal of the feedback module 110. The first terminal of the transistor serves as the first terminal of the voltage clamping module 120 and is connected to the cathode of the photodiode PD. The second terminal of the transistor serves as the second terminal of the voltage clamping module 120 and is connected to the anode of the photodiode PD. The feedback module 110 controls the conduction level of the transistor by adjusting the voltage at the control terminal of the transistor, thereby generating a stable voltage drop across the transistor. This voltage drop is the cathode voltage of the photodiode PD.

[0072] In one possible implementation, the feedback module 110 includes: an operational amplifier U2 and a transistor M; the non-inverting input of the operational amplifier U2 receives a reference voltage Vref, the inverting input of the operational amplifier U2 is connected to the source of the transistor M and the first terminal of the voltage clamping module 120, and the output of the operational amplifier U2 is connected to the gate of the transistor M; the drain of the transistor M serves as the output of the feedback module 110 and is connected to the input of the amplifier circuit 200; the source of the transistor M serves as the input of the feedback module 110 and is connected to the cathode of the photodiode PD.

[0073] The reference voltage Vref is equal to the target voltage; the transistor M is used to transfer the photocurrent generated by the photodiode PD from its source to its drain so that it flows into the input terminal of the amplifier circuit 200.

[0074] Operational amplifier U2 compares the cathode voltage Vc of photodiode PD with a reference voltage Vref. Based on the difference between the two, it outputs a control voltage Vg to the gate of transistor M, controlling the conduction level of transistor M and thus adjusting the current flowing through transistor M. After transistor M is turned on, the current path of feedback module 110 is established. The source current Is flowing from the source of transistor M is divided into two paths: one is the photocurrent Ipd generated by photodiode PD, which flows from the source of transistor M into the cathode of photodiode PD; the other is the clamping current Ic, which flows from the source of transistor M into voltage clamping module 120. Therefore, clamping current Ic = Is - Ipd.

[0075] The output voltage Vg of operational amplifier U2 is proportional to the difference between the reference voltage Vref and the cathode voltage Vc of photodiode PD, i.e., Vg = A × (Vref - Vc), where A is the open-loop gain of operational amplifier U2.

[0076] The reference voltage Vref is equal to the target voltage. When the cathode voltage Vc of the photodiode PD deviates from the target voltage, the operational amplifier U2 adjusts the output voltage Vg, changes the conduction level of the transistor M, adjusts the source current Is, thereby changing the clamping current Ic, causing the voltage across the voltage clamping module 120 to change, and finally stabilizes the cathode voltage Vc of the photodiode PD at the target voltage.

[0077] The high open-loop gain of operational amplifier U2 makes the error between the cathode voltage Vc of photodiode PD and the reference voltage Vref extremely small, achieving high-precision voltage clamping; transistor M transfers the photocurrent Ipd generated by photodiode PD from the source to the drain and flows into the input terminal of amplifier circuit 200, realizing low-noise and high-fidelity current transfer.

[0078] It should be noted that the feedback module 110, which includes an operational amplifier and a transistor, is only one example. The feedback module 110 can also be implemented in other ways. For example, the feedback module 110 can also adopt other circuit structures that can realize voltage-to-current conversion, such as transconductance amplifiers, current mirrors, or common-source cascode amplifiers, as long as they can generate a corresponding clamping current according to the cathode voltage of the photodiode and transfer the photocurrent to the amplifier circuit.

[0079] In one possible implementation, the feedback module 110 further includes a current source Ib connected to the drain of the transistor M, for providing a bias current Ibias to the transistor M, so as to provide at least a portion of the clamping current Ic to the voltage clamping module 120.

[0080] Specifically, the bias current Ibias provided by the current source Ib flows into the drain of transistor M, exits from the source of transistor M, and reaches the cathode of photodiode PD. Since the source current Is of transistor M is equal to the sum of the clamping current Ic flowing through voltage clamping module 120 and the photocurrent Ipd flowing through photodiode PD, and the drain current Id of transistor M is equal to the source current Is, and the drain current is equal to the bias current Ibias, then Ibias = Id = Is = Ic + Ipd. Therefore, the clamping current Ic = Ibias - Ipd. This bias current constitutes the basic component of the clamping current Ic. Under static (no light) conditions, the clamping current Ic is entirely provided by the bias current Ibias; under dynamic (with light) conditions, the clamping current Ic is composed of the bias current Ibias and the photocurrent Ipd, i.e., Ic = Ibias - Ipd.

[0081] For example, the bias current provided by the current source Ib can be flexibly set, so that the dynamic range of the clamping current Ic is adjustable to adapt to the changes in photocurrent under different lighting conditions.

[0082] For example, when the cathode voltage of the actual photodiode PD is not equal to the target voltage, the switch M acts as a voltage-controlled current source. The square of the difference between the control terminal voltage VGS and the threshold voltage VTH of the switch M is proportional to the magnitude of the clamping current Ic output by the switch M, as shown in the following formula:

[0083] For example, transistor M operates in the saturation region, acting as a voltage-controlled current source. Its drain current Id (i.e., the current flowing through transistor M) is related to the gate-source voltage V. GS and threshold voltage V TH It satisfies the following square law relationship:

[0084]

[0085] Where μn is the electron mobility, Cox is the capacitance per unit area of ​​the gate oxide layer, and W / L is the width-to-length ratio of the channel.

[0086] The above formula can be simplified to:

[0087]

[0088] In steady-state clamping, the cathode voltage of the photodiode PD is stabilized at the target voltage. At this time, the clamping current Ic flowing through the clamping resistor R is composed of the bias current and the photocurrent Ipd. The drain current Id of the transistor M is equal to Ic, and this current is transferred from the source to the drain through the transistor M, ultimately flowing into the input terminal of the amplifier circuit 200. During this process, the magnitude of the photocurrent Ipd remains unchanged and is completely transferred to the amplifier circuit 200.

[0089] For example, transistor M can be an NMOS transistor.

[0090] For example, the difference between the reference voltage and the cathode voltage clamp of the photodiode is proportional to the output voltage of the operational amplifier.

[0091] The operational amplifier continuously compares the voltage at its non-inverting input terminal with the voltage at its inverting input terminal. The difference between the two is the error voltage. The operational amplifier amplifies this tiny error voltage to produce a large output voltage. This output voltage is sent to the gate of transistor M to control the conduction level of M, thereby adjusting the current flowing through M (i.e., the clamping current).

[0092] In one possible implementation, the amplifier circuit 200 includes: a capacitor feedback transimpedance amplifier U1, an integrating capacitor Cint, and a reset switch rst; the inverting input terminal of the capacitor feedback transimpedance amplifier U1 serves as the input terminal of the amplifier circuit 200 and is connected to the output terminal of the clamping circuit 100; the integrating capacitor Cint and the reset switch rst are both connected across the inverting input terminal and the output terminal of the capacitor feedback transimpedance amplifier U1.

[0093] In this circuit, the anode of the photodiode is grounded, and the cathode is connected to the PD_K terminal, which is also the inverting input terminal VIN of the capacitor feedback transimpedance amplifier. The non-inverting input terminal of the capacitor feedback transimpedance amplifier receives the common-mode voltage VCM. The integrating capacitor is connected between the inverting input terminal and the output terminal of the capacitor feedback transimpedance amplifier as a feedback branch. The reset switch is connected in parallel with the integrating capacitor to reset the voltage across the integrating capacitor before integration, clearing the charge from the previous integration.

[0094] During the reset phase: the reset switch rst closes. At this time, the two ends of the integrating capacitor Cint are short-circuited by the reset switch rst, and the voltage across the integrating capacitor Cint is cleared to zero. Due to the virtual short characteristic of the capacitor feedback transimpedance amplifier U1, the voltage at its inverting input is clamped to the common-mode voltage VCM. Therefore, at the end of the reset phase, the output voltage VO of the capacitor feedback transimpedance amplifier U1 is equal to the common-mode voltage VCM, the circuit completes the reset, and is ready for the next integration.

[0095] During the integration phase: the reset switch rst is open. The photodiode PD generates a photocurrent Ipd when illuminated. This photocurrent flows from the cathode of the photodiode PD and is transferred through the clamping circuit 100 to the inverting input of the capacitive feedback transimpedance amplifier U1. Due to the virtual short characteristic of the capacitive feedback transimpedance amplifier U1, the voltage at its inverting input is stabilized at the common-mode voltage VICM. The photocurrent Ipd cannot flow into the interior of the capacitive feedback transimpedance amplifier U1; instead, it flows entirely through the integrating capacitor Cint, charging (i.e., extracting charge from the integrating capacitor Cint).

[0096] As the integrating capacitor Cint is charged, the voltage difference across it gradually increases. Based on the voltage-current relationship of the capacitor, the output voltage VO of the transimpedance amplifier U1 can be expressed as:

[0097]

[0098] Where Tint is the integration time, and if the light intensity is constant and the photocurrent Ipd is constant, then the output voltage can be simplified to:

[0099]

[0100] From the above formula, it can be seen that the output voltage change ΔVO of the capacitor feedback transimpedance amplifier U1 is directly proportional to the product of the photocurrent Ipd and the integration time Tint (i.e., the total extracted charge Qout = Ipd × Tint) and inversely proportional to the integrating capacitor Cint, that is:

[0101] ΔVO = Qout / Cint

[0102] Therefore, by measuring the output voltage VO of the capacitor feedback transimpedance amplifier U1, the magnitude of the photocurrent generated by the photodiode PD can be accurately calculated, and the incident light intensity can be deduced from there.

[0103] The clamping circuit 100 and the amplifier circuit 200 work in concert: Throughout the integration process, the clamping circuit 100 consistently stabilizes the cathode voltage of the photodiode PD at the target voltage (i.e., the reference voltage Vref), ensuring it is unaffected by changes in the output voltage of the transimpedance amplifier U1. Simultaneously, the clamping circuit 100 transmits the photocurrent Ipd generated by the photodiode PD completely and without loss to the inverting input of the transimpedance amplifier U1, ensuring that the current flowing into the integrating capacitor Cint is precisely equal to the photocurrent Ipd, without altering its magnitude. This synergistic effect guarantees a highly linear relationship between the output voltage and photocurrent of the transimpedance amplifier U1, thereby achieving high-precision light intensity detection.

[0104] In one possible implementation, the output voltage of the capacitive feedback transimpedance amplifier is equal to the sum of the common-mode voltage and the integral voltage increment of the amplifier; the integral voltage increment is equal to the ratio of the integral value of the photocurrent generated by the photodiode over the integration time to the capacitance of the integrating capacitor.

[0105] A precise linear relationship is established between the output voltage of the capacitor feedback transimpedance amplifier U1 and the photocurrent generated by the photodiode PD. This linear relationship ensures that the output voltage of the amplifier circuit 200 can accurately and without distortion reflect the incident light intensity, thereby improving the accuracy of light detection.

[0106] In this embodiment, a capacitive transimpedance amplifier circuit is used to convert the weak current drawn from the integrating capacitor into a stable voltage output, thereby achieving low-noise and high-linearity photoelectric conversion.

[0107] This application also provides a chip including the aforementioned photosensitive circuit.

[0108] This application also provides an electronic device including the chip described above.

[0109] For example, the electronic device is a photodetector, which can be flexibly applied to various scenarios that require converting light signals into electrical signals for detection, measurement or control, and is not limited here.

[0110] The following provides an exemplary description of the application scenarios of the optical detection device provided in this application.

[0111] For example, in industrial automation scenarios, optical detection devices can be used to perform object presence detection, location positioning, counting, and sorting on a production line.

[0112] For example, in robot control or autonomous driving scenarios, optical detection devices can be used to perform environmental scanning and navigation obstacle avoidance.

[0113] For example, in the field of electronic devices, light detection devices can be installed in electronic devices such as mobile phones and tablets to perform operations such as automatically adjusting screen brightness according to ambient light, turning off the screen when a face is detected approaching, and achieving fast focusing through laser ranging.

[0114] For example, in the field of communications, optical detection devices can be used to convert light pulses into electrical signals for fiber optic communication, enabling high-speed data transmission.

[0115] For example, in the medical and health field, optical detection devices can be applied to blood oxygen measurement, heart rate measurement with fluorescence detection, and DNA sequencing. Taking blood oxygen measurement as an example, optical detection devices can use red and infrared light transmitted through a finger to calculate blood oxygen saturation through photoelectric detection.

[0116] For example, in security monitoring scenarios, optical detection devices can be used for night vision and perimeter intrusion detection.

[0117] For example, in the automotive field, optical detection devices can be used to detect water droplets on the windshield to control wipers, recognize user gestures, and so on.

[0118] The photodetector provided in this application embodiment can effectively improve the linearity of the photodetector output result to the photocurrent and improve the accuracy of photodetection by using the above-described photosensitive circuit.

[0119] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of this application are indicated by the following claims.

[0120] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this application is limited only by the appended claims.

Claims

1. A photosensitive circuit, characterized in that, include: Photodiodes, amplifier circuits, and clamping circuits; The output terminal of the clamping circuit is connected to the input terminal of the amplifier circuit, the input terminal of the clamping circuit is connected to the cathode of the photodiode, and the anode of the photodiode is grounded. The clamping circuit is used to clamp the cathode voltage of the photodiode to the target voltage and to transfer the photocurrent generated by the photodiode to the input terminal of the amplifier circuit.

2. The circuit according to claim 1, characterized in that, The clamping circuit includes: a feedback module and a voltage clamping module; The input terminal of the feedback module serves as the input terminal of the clamping circuit, and the output terminal of the feedback module serves as the output terminal of the clamping circuit. It is used to output clamping current according to the cathode voltage of the photodiode and to transmit the photocurrent generated by the photodiode to the input terminal of the amplifier circuit. The first end of the voltage clamping module is connected to the input end of the feedback module, and the second end of the voltage clamping module is connected to the anode of the photodiode, for stabilizing the cathode voltage of the photodiode at the target voltage based on the clamping current.

3. The circuit according to claim 2, characterized in that, The voltage clamping module includes: a clamping resistor; The first end of the clamping resistor serves as the first end of the voltage clamping module, and the second end of the clamping resistor serves as the second end of the voltage clamping module.

4. The circuit according to claim 3, characterized in that, The feedback module includes: an operational amplifier and a transistor; The non-inverting input of the operational amplifier receives a reference voltage, the inverting input of the operational amplifier serves as the input of the feedback module, and the output of the operational amplifier is connected to the gate of the transistor. The drain of the transistor serves as the output terminal of the feedback module, and the source of the transistor is connected to the inverting input terminal of the operational amplifier. Wherein, the magnitude of the reference voltage is equal to the target voltage; The transistor is used to transfer the photocurrent generated by the photodiode from its source to its drain so that it flows into the input terminal of the amplifier circuit.

5. The circuit according to claim 4, characterized in that, The feedback module also includes: A current source, connected to the drain of the transistor, is used to provide bias current to the transistor in order to provide clamping current to the voltage clamping module.

6. The circuit according to claim 4, characterized in that, When the transistor is operating in saturation, the square of the difference between the output voltage of the operational amplifier and the threshold voltage of the transistor is proportional to the magnitude of the clamping current. And / or, the difference between the reference voltage and the cathode voltage clamp of the photodiode is proportional to the output voltage of the operational amplifier.

7. The circuit according to any one of claims 1-6, characterized in that, The amplifier circuit includes: a capacitor feedback transimpedance amplifier, an integrating capacitor, and a reset switch; The inverting input terminal of the capacitor feedback transimpedance amplifier serves as the input terminal of the amplifier circuit and is connected to the output terminal of the clamping circuit. Both the integrating capacitor and the reset switch are connected across the inverting input and output of the capacitor feedback transimpedance amplifier.

8. The circuit according to claim 7, characterized in that, The output voltage of the capacitor feedback transimpedance amplifier is equal to the sum of the common-mode voltage and the integral voltage increment of the capacitor feedback transimpedance amplifier. The integral voltage increment is equal to the ratio of the integral value of the photocurrent generated by the photodiode during the integral time to the capacitance value of the integral capacitor.

9. A chip, characterized in that, Includes the light-sensing circuit as described in any one of claims 1-8.

10. An electronic device, characterized in that, Includes the chip described in claim 9.

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