Light sensor circuit

Abstract

A light sensor circuit includes a photodiode and a capacitor unit. By controlling the capacitor unit to maintain the photodiode's cathode at the same or similar voltage level as the photodiode's anode, the effects of the photodiode's dark current can be significantly reduced. When the light sensor circuit is used in an analog-to-digital conversion device, the performance and accuracy of the device can be effectively maintained, while significantly reducing circuit design difficulty and manufacturing costs.

Description

Technical Field

[0001] The present invention relates to a light sensor circuit, and more particularly to a light sensor circuit using a photodiode. Background Art

[0002] Light sensors, implemented using light-sensing technology, are widely used in many applications. For example, ambient light sensors (ALS) are used in electronic products to detect ambient light intensity and adjust display brightness. Light sensors can also be used to measure distance or position in space. For example, mobile devices often include proximity sensors that can detect the distance between a user's face and the electronic device's display. When the proximity sensor is close to the user's face, the electronic device can disable the display and touch functions.

[0003] Generally speaking, light sensors require an analog-to-digital converter (ADC) to convert the analog input signal generated by sensing light into a digital signal that can be processed by digital circuits. There are many different types of ADCs, each with different operating mechanisms, characteristics, and functions. Chinese Patent Publication No. 107124184 discloses an ADC with a high dynamic range and high linearity. This ADC utilizes an integration unit and other corresponding circuitry to convert an analog input signal obtained by sensing light from a photodiode into a digital signal.

[0004] However, the problem encountered by this analog-to-digital conversion device is that the photodiode has characteristics such as junction capacitance and dark current. Figure 1 As shown, the signal of a light sensor circuit 9 is derived from a photocurrent generated by a photodiode 90, wherein the photocurrent includes a dark current I DARK and light current I PD In order to improve the linearity of the sensor, it is necessary to pre-calibrate the dark current I DARK , so as to avoid affecting the integration unit 92 and reducing the accuracy of the sensing result.

[0005] Although the applicant's previously filed Chinese patent application No. 112449126 has proposed a light sensor circuit 8 that can reduce the junction capacitance of the photodiode 80 to improve the charging and discharging speed and accuracy of the analog front-end circuit. Figure 2As shown in FIG. 1 , the patent application must use a voltage follower 82 to control the bias voltage across the photodiode 80. Therefore, additional consideration must be given to the driving capability, error value, and other conditions of the operational amplifier or corresponding circuit used to constitute the voltage follower 82. Figure 1 As shown, if the integration unit 92 actually operates at a reference voltage VCM, the design difficulty of the patent case will be further increased.

[0006] In view of the above problems, the present invention provides another light sensor circuit to solve the problems of junction capacitance or dark current of the photodiode. Summary of the Invention

[0007] The present invention provides a light sensor circuit comprising a photodiode and a capacitor unit. By controlling the capacitor unit to maintain the cathode of the photodiode at a voltage level equal to or close to that of the anode, the photodiode's visible junction capacitance approaches zero, significantly reducing the effects of the photodiode's dark current. Consequently, when the light sensor circuit is used in an analog-to-digital conversion device, the performance and accuracy of the analog-to-digital conversion device can be effectively maintained. Furthermore, the present invention reduces the effects of the photodiode's dark current by utilizing only a simple circuit structure consisting of capacitor elements and switch elements, significantly reducing circuit design complexity and manufacturing costs.

[0008] The present invention relates to a light sensor circuit comprising a photodiode, an integrating unit, and a capacitor unit. The cathode of the photodiode is coupled to a first side of the capacitor unit, an integrating input terminal of the integrating unit is coupled to a second side of the capacitor unit, two terminals of an integrating capacitor of the integrating unit are coupled to the first side of the capacitor unit and an integrating output terminal of the integrating unit, respectively, and a switch element of the capacitor unit is coupled between the anode of the photodiode and the first side of the capacitor unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 : It is a partial circuit diagram of an existing analog-to-digital conversion circuit;

[0010] Figure 2 :It is a partial circuit diagram of an existing light sensor circuit;

[0011] Figure 3 : It is a structural diagram of a light sensor circuit according to an embodiment of the present invention;

[0012] Figure 4 : It is a schematic diagram of the relationship between the dark current and temperature of the photodiode in the prior art and the embodiment of the present invention; and

[0013] Figure 5 : It is a structural diagram of a light sensor circuit according to another embodiment of the present invention.

[0014]

Figure number comparison

[0015] 1 Light sensor circuit

[0016] 10 Photodiode

[0017] 12 Integral Unit

[0018] 14 capacitor units

[0019] 14a First side

[0020] 14b Second side

[0021] 140 holding capacitor

[0022] 142 Switching elements

[0023] 144 control unit

[0024] 146 Switching elements

[0025] V IN Integral input

[0026] V OUT Integral output

[0027] Cf integrating capacitor

[0028] VCM reference voltage

[0029] I PD Light current

[0030] I DARK Dark current

[0031] Vdiff bias

[0032] 9.8 Light sensor circuit

[0033] 90, 80 photodiode

[0034] 92 Integral Unit

[0035] 82 Voltage Follower DETAILED DESCRIPTION

[0036] In order to further understand and appreciate the structural features and effects achieved by the present invention, preferred embodiments and detailed descriptions are provided as follows:

[0037] Certain terms are used in the specification and claims to refer to specific components. However, a person of ordinary skill in the art to which the present invention relates may use different terms to refer to the same component. Furthermore, the specification and claims do not distinguish components by name, but rather by overall technical differences. The term "including" as used throughout the specification and claims is an open-ended term and should be interpreted as "including but not limited to." Furthermore, the term "coupled" includes both direct and indirect connection methods. Therefore, if a first device is described as being coupled to a second device, it means that the first device can be directly connected to the second device, or can be indirectly connected to the second device through other devices or other connection methods, so that signals can be transmitted between the first and second devices.

[0038] See also Figure 3 , which is a schematic diagram of the architecture of a light sensor circuit 1 according to one embodiment of the present invention. As shown, light sensor circuit 1 includes a photodiode 10, an integrating unit 12, and a capacitor unit 14. The anode of photodiode 10 is coupled to a common signal terminal of the system, represented by ground in this embodiment, but the present invention is not limited thereto. The cathode of photodiode 10 is coupled to a first side 14a of capacitor unit 14.

[0039] The integration unit 12 is applied to the integration circuit of the analog-to-digital conversion device, and includes an integration input terminal V IN , an integral output terminal V OUT And an integrating capacitor Cf, the integrating input terminal V IN is coupled to a second side 14b of the capacitor unit 14, and two ends of the integrating capacitor Cf are coupled to the first side 14a of the capacitor unit 14 and the integrating output terminal V OUT In this embodiment, a basic integration circuit implemented by an operational amplifier is used as an example. Therefore, the integration unit 12 includes an operational amplifier. A non-inverting input terminal of the operational amplifier can receive a reference voltage VCM, and an inverting input terminal of the operational amplifier is the integration input terminal V IN , one output terminal of the operational amplifier is the integral output terminal V OUT .

[0040] In other words, compared to Figure 1 In the prior art, both ends of the integration capacitor Cf of the integration unit 92 are coupled to the integration input terminal V IN With the integral output V OUT In this embodiment, the capacitor unit 14 is additionally provided, and the two ends of the integrating capacitor Cf are respectively coupled to the first side 14a of the capacitor unit 14 and the integral output terminal V OUT , then the integral input terminal VIN coupled to the second side 14 b of the capacitor unit 14 .

[0041] The detailed structure and operation of the capacitor unit 14 are described in detail below. The capacitor unit 14 includes a holding capacitor 140, a switch element 142 and a control unit 144. The two ends of the holding capacitor 140 are the first side 14a and the second side 14b of the capacitor unit 14. The switch element 142 is coupled between the anode of the photodiode 10 and the first side 14a. The control unit 144 is coupled to the switch element 142 to control whether it is turned on or off. During the time period when the integration unit 12 has not yet performed the integration operation, the control unit 144 controls the switch element 142 to be turned on, so that the first side 14a of the capacitor unit 14 maintains the same voltage level as the anode of the photodiode 10. In this embodiment, the anode of the photodiode 10 is coupled to the ground terminal, so the switch element 142 can be coupled between the ground terminal and the first side 14a. Thus, when the control unit 144 controls the switch element 142 to be turned on, the first side 14 a of the capacitor unit 14 can be kept at the ground voltage.

[0042] The control unit 144 controls the switch element 142 to be turned off during the time interval when the integration unit 12 performs the integration operation. PD The integrating capacitor Cf enables the integrating unit 12 to perform an integrating operation. The holding capacitor 140 of the capacitor unit 14 can maintain a voltage difference even after the switch element 142 is turned off, thereby maintaining the first side 14a of the capacitor unit 14 at a voltage level that is the same as or close to the anode voltage of the photodiode 10 (i.e., ground voltage in this embodiment). Thus, even if the reference voltage VCM received by the non-inverting input terminal of the operational amplifier is not ground voltage in this embodiment, the first side 14a of the capacitor unit 14 can still be maintained at ground voltage or at least close to ground voltage, maintaining the photodiode 10 at or near zero bias. The switch element 142 can be formed by a metal oxide semiconductor field effect transistor (MOSFET), a bipolar junction transistor (BJT), or other circuit switching element.

[0043] The so-called dark current I DARK When the photodiode does not receive light, the current generated by the photodiode itself is affected by the bias voltage. The current formula is as follows:

[0044]

[0045] Among them, I CO is the reverse saturation current, V T(unit: V) is the temperature T (unit: °K) / 11600, which is positively correlated with temperature, V is the photodiode bias value, and η is the photodiode material coefficient. From the above formula, it can be seen that if the photodiode bias is 0V, it will not be affected by the coefficient V T Affects its dark current.

[0046] Accordingly, by maintaining the first side 14a of the capacitor unit 14 at a voltage level equal to or close to that of the anode of the photodiode 10, the embodiment of the present invention can maintain the photodiode 10 at or near zero bias, thereby preventing the photodiode 10 from being affected by transient voltage fluctuations. This means that the junction capacitance of the photodiode 10 does not generate charge or discharge currents. Consequently, the light sensor circuit 1 of the present invention can effectively reduce the apparent junction capacitance of the photodiode 10 to near zero, significantly reducing the impact of dark current on the photodiode 10.

[0047] In contrast, Figure 1 As shown, in the prior art, both ends of the integration capacitor Cf of the integration unit 92 are coupled to the integration input terminal V IN With the integral output V OUT At this time, if a non-inverting input terminal of the integration unit 12 receives a reference voltage VCM for operation, due to the virtual short-circuit characteristic of the operational amplifier, the reference voltage VCM will be coupled to the integration input terminal V IN If the reference voltage VCM is not equal to the anode voltage of the photodiode 90, a non-zero bias voltage Vdiff is formed across the photodiode 90. In this case, the photodiode 90 will inevitably be affected by temperature and generate dark current.

[0048] Please refer to Figure 4 As shown in FIG. 1 , S1 is a curve showing the relationship between the dark current and temperature of the photodiode 90 in the prior art, and S2 is a curve showing the relationship between the dark current and temperature of the photodiode 10 in the aforementioned embodiment of the present invention. Comparing S1 and S2, it can be seen that the aforementioned embodiment of the present invention, by controlling the photodiode 10 to maintain a zero bias or near-zero bias state, can indeed significantly reduce the impact of the dark current of the photodiode 10, and this effect becomes more significant as the temperature rises.

[0049] It should be noted that, although the control unit 144 of the capacitor unit 14 in this embodiment can be a standalone circuit for generating the control signal required to control the switch element 142, in practice, analog-to-digital conversion devices all have a frequency control signal that determines whether the integration unit 12 performs an integration operation. Therefore, the control unit 144 can be integrated into the control circuit of the analog-to-digital conversion device to directly use the analog-to-digital conversion device's existing frequency control signal to control the switching element 142 to be turned on or off.

[0050] Please refer to Figure 5 FIG. 1 is a schematic diagram of a light sensor circuit 1 according to another embodiment of the present invention. The difference from the above embodiment is that the capacitor unit 14 includes another switch element 146, which is coupled to the integral input terminal V IN With the integral output V OUT The control unit 144 is coupled to the other switch element 146 to control it to be turned on or off synchronously with the switch element 142. In this way, the control unit 144 controls the other switch element 146 to be turned on during the time interval when the integration unit 12 has not yet performed the integration operation, so that the second side 14b of the capacitor unit 14 remains connected to the integration output terminal V OUT The control unit 144 controls the other switch element 146 to be turned off during the time interval when the integration unit 12 performs the integration operation. IN With the integral output V OUT There is no longer any signal conduction path other than the integrating capacitor Cf and the holding capacitor 140 , so that the integrating unit 12 performs an integrating operation.

[0051] By additionally providing the other switch element 146, when the integration unit 12 has not yet performed the integration operation, the second side 14b of the capacitor unit 14 is controlled to maintain contact with the integration output terminal V OUT The same voltage level, when the integration unit 12 performs an integration operation, the holding capacitor 140 of the capacitor unit 14 is more likely to maintain a voltage difference, so that the first side 14a of the capacitor unit 14 maintains the same or close voltage level as the anode of the photodiode 10.

[0052] In summary, the present invention provides a light sensor circuit comprising a photodiode and a capacitor unit. By controlling the capacitor unit to maintain the photodiode's cathode at or near the same voltage level as the photodiode's anode, the photodiode's apparent junction capacitance approaches zero, significantly reducing the effects of the photodiode's dark current. Consequently, when the light sensor circuit is used in an analog-to-digital converter, the performance and accuracy of the converter can be effectively maintained.

[0053] Furthermore, compared to the aforementioned prior art, in which the voltage across the photodiode is controlled by a voltage follower composed of circuits such as an operational amplifier or a common-drain amplifier, in each embodiment of the present invention, the same technical effect can be achieved only through simple circuit structures such as capacitor elements and switch elements, significantly reducing the difficulty of circuit design and manufacturing costs.

[0054] The above is only a preferred embodiment of the present invention and is not intended to limit the scope of the present invention. All equivalent changes and modifications in the shape, structure, characteristics and spirit described in the scope of the claims of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A light sensor circuit, characterized in that: It includes: a photodiode comprising an anode and a cathode; an integration unit comprising an integration input terminal, an integration output terminal, and an integration capacitor; and A capacitor unit includes a holding capacitor and a switch element, wherein two ends of the holding capacitor are a first side and a second side of the capacitor unit; The cathode of the photodiode is coupled to the first side of the capacitor unit, the integral input terminal is coupled to the second side of the capacitor unit, the two ends of the integral capacitor are coupled to the first side of the capacitor unit and the integral output terminal respectively, and the switching element is coupled between the anode of the photodiode and the first side of the capacitor unit.

2. The light sensor circuit according to claim 1, wherein: in, The capacitor unit further includes a control unit, which is coupled to the switch element to control the switch element to be turned on or off.

3. The light sensor circuit according to claim 2, wherein: in, The control unit controls the switch element to be turned on during a time interval when the integration unit has not yet performed an integration operation; Furthermore, during the time interval when the integration unit performs the integration operation, the switch element is controlled to be cut off.

4. The light sensor circuit according to claim 1, wherein: in, The capacitor unit includes another switch element coupled between the integration input terminal and the integration output terminal of the integration unit.

5. The light sensor circuit according to claim 4, wherein: in, The capacitor unit further includes a control unit coupled to the switch element and the other switch element to control on / off.

6. The light sensor circuit according to claim 5, wherein: in, The control unit controls the switch element and the other switch element to be turned on during a time interval in which the integration unit has not yet performed an integration operation; Furthermore, during the time interval when the integration unit performs the integration operation, the switch element and the other switch element are controlled to be turned off.

7. The light sensor circuit according to claim 1, wherein: in, The integration unit includes an operational amplifier. A non-inverting input terminal of the operational amplifier receives a reference voltage. An inverting input terminal of the operational amplifier serves as the integration input terminal. An output terminal of the operational amplifier serves as the integration output terminal.

8. The light sensor circuit according to claim 7, wherein: in, The reference voltage is not equal to the anode voltage of the photodiode.

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