Ambient light elimination method, light detection sensor and system
By directly eliminating ambient photocurrent through photodiodes and analog feedback loops, the problem of analog front-end saturation caused by ambient light interference is solved, improving the ambient photocurrent elimination range and detection accuracy of proximity light detection sensors.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-28
- Publication Date
- 2026-04-14
AI Technical Summary
In existing technologies, ambient light interference affects the detection accuracy of proximity light detection sensors and may cause analog front-end saturation, which is difficult to eliminate effectively.
An analog feedback loop composed of photodiodes, integrator modules, current compensation modules, and chopper modulation modules is used to directly cancel ambient photocurrent before analog-to-digital conversion, thus achieving front-end analog cancellation.
The ambient photocurrent elimination range of the proximity light detection sensor has been improved, the elimination time has been reduced, the delay and accuracy limitations of digital processing have been avoided, and the detection accuracy has been improved.
Smart Images
Figure CN121856936A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of proximity light sensor technology, specifically relating to an ambient light elimination method, a light detection sensor, and a system. Background Technology
[0002] In the field of mobile phones and tablets, high-performance optical sensor chips are used as standard configurations for proximity light detection. System designers can automatically adjust the brightness of the display screen according to the distance between the display screen and the object being measured, thereby reducing system power consumption.
[0003] In current mobile devices, the performance of proximity sensors directly impacts power consumption and user experience. Traditional solutions face significant challenges in detecting weak reflected signals from objects due to the attenuation effect of infrared light on displays and the stringent requirements on LED turn-on times. Ambient light interference not only affects detection accuracy but can also lead to saturation of subsequent circuitry.
[0004] Existing technical solutions provide compensation control signals through digital signal processing, introducing a feedback current DAC at the system input to compensate for ambient light and minimize the ambient light entering the analog front end. For example... Figure 1 As shown, it consists of an LED emitter and a proximity light detection receiver. Switch SW controls the LED's emission timing. The photodiode receives light signals from the LED and ambient light signals, transmits them to the analog front-end (AFE) for conversion into electrical signals, and then the analog-to-digital converter (ADC) generates digital signals (Data) for system-level digital signal processing. Since ambient light is considered external interference and poses a risk of saturating the AFE output, it requires specific processing. Summary of the Invention
[0005] The purpose of this invention is to provide an ambient light cancellation method, a light detection sensor, and a system, which solves the problem in the prior art that when ambient light is cancelled by controlling a current-feedback digital-to-analog converter (ambient DAC) through digital signal processing, there is a risk that ambient light is an external interference and that the analog front-end AFE output will be saturated.
[0006] The objective of this invention can be achieved through the following technical solutions: The light detection sensor includes: A photodiode is used to receive optical signals and convert them into electrical signals. An integrator module, whose input is connected to the photodiode, is used to integrate the difference current between the current signal and the compensation current and output a voltage signal. A current compensation module is used to obtain a compensation control signal based on the voltage signal and generate the compensation current through the compensation control signal. The chopper modulation module is used to receive the differential current, input the differential current to the integrator module, and generate a periodically switching chopper control signal to control the optical detection sensor to work alternately between the calibration stage and the detection stage. During the calibration phase, the light signal is the ambient light signal, and the current compensation module dynamically adjusts the compensation current according to the compensation control signal to counteract the current signal generated by the ambient light signal and establish a compensation state. During the detection phase, the light signal is an ambient light signal and an LED light signal. The current compensation module maintains the established compensation state and continues to cancel the current signal generated by the ambient light signal through the compensation current, so that the integrator module only integrates the current signal corresponding to the LED light signal.
[0007] As a further aspect of the present invention, the current compensation module includes: An error amplification module, whose input is connected to the output of the integrator module, is used to amplify the error between the voltage signal and the first reference voltage and output a compensation control signal. A sample-and-hold module, whose input is connected to the output of the error amplification module, is used to track and sample the compensation control signal during the calibration phase and hold the compensation control signal during the detection phase. A controlled current source, the control terminal of which is connected to the output terminal of the sample-and-hold module, and its output current is used as the compensation current.
[0008] As a further aspect of the present invention, a bias current source is also included, which is connected to the input terminal of the integrator module and its operating state is controlled by a first switch; the first switch is turned on during the calibration and detection phases and turned off at other times.
[0009] The present invention also discloses an ambient light cancellation method applied to the above-mentioned light detection sensor, the method comprising: During the calibration phase, an ambient light signal is received and an ambient light current is generated. The ambient light current is integrated to obtain an ambient light voltage signal. A compensation control signal is obtained based on the ambient light voltage signal, and a compensation current is generated through the compensation control signal to counteract the ambient light current. During the detection phase, an optical signal is received and a current signal is generated. The optical signal includes an LED optical signal and an ambient light signal. The compensation control signal is kept unchanged, and a compensation current is generated through the compensation control signal to continue to cancel the current signal corresponding to the ambient light signal, so as to obtain the current signal corresponding to the LED optical signal.
[0010] As a further aspect of the present invention, the calibration phase and the detection phase are alternately controlled by a periodically switching chopper control signal.
[0011] The present invention also discloses a light detection system, including the above-mentioned light detection sensor, an LED load, and a control switch. The control switch is used to control the light emission timing of the LED load so that the light detection sensor receives an ambient light signal or an LED light signal and an ambient light signal.
[0012] The beneficial effects of this invention are: This invention abandons the traditional approach of relying on digital signal processing (DSP) and digital-to-analog converters (DAC) for post-compensation, and proposes a front-end analog direct cancellation mechanism. In the initial stage of the signal chain, i.e. before analog-to-digital conversion, the ambient photocurrent is directly canceled through an analog feedback loop, avoiding the delay and accuracy limitations caused by digital processing.
[0013] This invention can reduce ambient light interference in proximity light detection sensors to avoid saturation of subsequent circuits, improve the dynamic range of input signals, and achieve fast and synchronous ambient light elimination. Attached Figure Description
[0014] The invention will now be further described with reference to the accompanying drawings.
[0015] Figure 1 This is a schematic diagram of a scheme in the prior art that provides compensation control signals through digital signal processing; Figure 2 This is a circuit diagram of a light detection sensor according to the present invention; Figure 3 This is the timing diagram of the chopper modulation module. Detailed Implementation
[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0017] A light detection sensor, such as Figure 2 As shown, it includes: a photodiode, a chopper modulation module, an integrator module, an error amplifier module (Aerr(s)), a sample-and-hold module (S / H), a PMOS current source, a bias current source (IBIAS), and an analog-to-digital converter (ADC). The photodiode is used to convert the received optical signal into a current signal. The anode of the photodiode is grounded, and the cathode is connected to the virtual ground input node of the integrator via a chopper modulation module. The integrator module includes an operational amplifier, a feedback capacitor, and a reset switch connected in parallel with the feedback capacitor. The input terminal of the integrator module is connected to the photodiode, and is used to integrate the difference current between the current signal and the compensation current and output a voltage signal. The chopper modulation module synchronously controls the working state (sampling / holding) of the sample-and-hold module and the LED switch based on the chopper modulation signal; The chopper modulation module is used to receive the differential current, input the differential current to the integrator module, and generate a periodically switching chopper control signal to control the alternation of the calibration phase and the detection phase. The inverting input of the operational amplifier is a virtual ground node, which receives the combined signal of the photodiode current and the compensation current; the non-inverting input of the operational amplifier is grounded or connected to a fixed bias.
[0018] The integrator's output is compared with the reference voltage VREF and connected to the inverting input of the error amplifier, while the output is sent to the analog-to-digital converter (ADC) for digitization. The input terminal of the integrator module is connected to the photodiode, and is used to integrate the difference current between the current signal and the compensation current and output a voltage signal. The input of the analog-to-digital converter (ADC) is connected to the output of the integrator module. The ADC converts the integrated analog voltage into a digital signal for subsequent processing.
[0019] The inverting input of the error amplifier module receives the output voltage of the integrator, the non-inverting input of the error amplifier module is connected to the reference voltage VREF, and the output of the error amplifier module generates a compensation voltage VCTRL, which is used to control the PMOS current source. The input of the sample-and-hold module is connected to the compensation voltage VCTRL output by the error amplifier. The sample-and-hold module samples and tracks the compensation voltage VCTRL in the Chop0 stage (calibration stage) and holds the compensation voltage VCTRL in the Chop1 stage (detection stage). The output of the sample-and-hold module controls the gate of the PMOS current source. The source of the PMOS current source is connected to the power supply voltage, the gate is controlled by the output voltage of the sample-and-hold module, and the drain outputs a compensation current. This current is injected into the integrator input node through a chopper modulation module. The bias current source is connected to the integrator input node via a switch controlled by the Chop2 signal to provide bias when the ambient photocurrent is very small, ensuring compensation current matching.
[0020] like Figure 3 As shown, the sensor operates as follows: Chop0 stage (calibration stage): LEDs are off, and the circuit is dedicated to detecting ambient light and quickly establishing the corresponding compensation current; at this time, the sample-and-hold module is in sampling mode, tracking and locking the compensation voltage VCTRL. Specifically: When the LED light control switch is off, the photodiode only receives the ambient light signal and it flows forward into the integrator module for conversion. The sample-and-hold module S / H is in the sampling phase. At this time, the output voltage of the integrator module begins to deviate from the reference voltage VREF and enters the negative input terminal of the error amplifier module. Under the amplification effect of the error amplifier module, a compensation voltage VCTRL is generated at its output terminal. The compensation voltage VCTRL controls the PMOS current source to generate a certain amount of current. The difference between this current and the bias current IBIAS forms the compensation current.
[0021] From a polarity perspective, the compensation current cancels out the input ambient light, forming negative feedback, which ultimately stabilizes the integrator output voltage near the reference voltage VREF, thus completing the ambient light compensation. If the ambient light current exceeds the integrator's range; If the compensation setup process can be completed within the integration period, ambient light can be eliminated, thereby improving the ambient light current elimination range of the proximity light detection sensor.
[0022] The purpose of the bias current IBIAS is to ensure that the compensation current matches the magnitude of the ambient photocurrent even when the ambient photocurrent is very small. Its conduction is controlled by the chop2 signal, and it is turned off the rest of the time to better stabilize the voltage of the photodiode PD.
[0023] Chop1 stage (detection stage): The LED is turned on, the sample-and-hold module is in hold mode, maintaining the compensation voltage from the previous stage, keeping the feedback current constant, thus amplifying and converting only the LED reflected signal. Specifically: When the LED light control switch is turned on, the proximity light detection receiver simultaneously receives the ambient light signal and the LED light signal, which flow back into the integrator for conversion. At this time, the sample-and-hold module is in the hold phase, keeping the voltage VCTRL constant and the compensation current is the same as the value established in the chop0 phase, thus eliminating the ambient light current. At this time, the current signal entering the integrator is only the LED photocurrent signal.
[0024] This invention abandons the traditional approach of relying on digital signal processing (DSP) and digital-to-analog converters (DAC) for post-compensation, and proposes a front-end analog direct cancellation mechanism. In the initial stage of the signal chain, i.e. before analog-to-digital conversion, the ambient photocurrent is directly canceled through an analog feedback loop, avoiding the delay and accuracy limitations caused by digital processing.
[0025] Test and Results Analysis Table 1. Comparison of Current Test Data Ambient photocurrent elimination range Current elimination loop settling time Original plan 180n Tled + Tdigital This invention 1000n <0.5Tled As shown in the test results in Table 1, the present invention improves the ambient light current elimination range of the proximity light detection sensor by 5.6 times, while reducing the ambient light elimination time to 0.5Tled.
[0026] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.
Claims
1. A light detection sensor, characterized in that, include: A photodiode is used to receive optical signals and convert them into electrical signals. An integrator module, whose input is connected to the photodiode, is used to integrate the difference current between the current signal and the compensation current and output a voltage signal. A current compensation module is used to obtain a compensation control signal based on the voltage signal and generate the compensation current through the compensation control signal. The chopper modulation module is used to receive the differential current, input the differential current to the integrator module, and generate a periodically switching chopper control signal to control the optical detection sensor to work alternately between the calibration stage and the detection stage. During the calibration phase, the light signal is the ambient light signal, and the current compensation module dynamically adjusts the compensation current according to the compensation control signal to counteract the current signal generated by the ambient light signal and establish a compensation state. During the detection phase, the light signal is an ambient light signal and an LED light signal. The current compensation module maintains the established compensation state and continues to cancel the current signal generated by the ambient light signal through the compensation current, so that the integrator module only integrates the current signal corresponding to the LED light signal.
2. The optical detection sensor according to claim 1, characterized in that, The current compensation module includes: An error amplification module, whose input is connected to the output of the integrator module, is used to amplify the error between the voltage signal and the first reference voltage and output a compensation control signal. A sample-and-hold module, whose input is connected to the output of the error amplification module, is used to track and sample the compensation control signal during the calibration phase and hold the compensation control signal during the detection phase. A controlled current source, the control terminal of which is connected to the output terminal of the sample-and-hold module, and its output current is used as the compensation current.
3. The optical detection sensor according to claim 2, characterized in that, It also includes a bias current source, which is connected to the input terminal of the integrator module and its working state is controlled by a first switch; the first switch is turned on during the calibration and detection phases and turned off at other times.
4. The optical detection sensor according to claim 1, characterized in that, The integrator module includes an operational amplifier, a feedback capacitor, and a reset switch; The inverting input of the operational amplifier forms a virtual ground node, which serves as the input of the integrator module and is used to receive the combined signal of the current signal and the compensation current. The non-inverting input of the operational amplifier is connected to a second reference voltage; The feedback capacitor is connected between the inverting input terminal and the output terminal of the operational amplifier; The reset switch is connected in parallel with the feedback capacitor.
5. The light detection sensor according to any one of claims 4, characterized in that, It also includes an analog-to-digital converter, whose input is connected to the output of the integrator module, for converting the integrated analog signal into a digital signal.
6. An ambient light cancellation method, applied to the light detection sensor according to any one of claims 1 to 5, characterized in that, The method includes: During the calibration phase, an ambient light signal is received and an ambient light current is generated. The ambient light current is integrated to obtain an ambient light voltage signal. A compensation control signal is obtained based on the ambient light voltage signal, and a compensation current is generated through the compensation control signal to counteract the ambient light current. During the detection phase, an optical signal is received and a current signal is generated. The optical signal includes an LED optical signal and an ambient light signal. The compensation control signal is kept unchanged, and a compensation current is generated through the compensation control signal to continue to cancel the current signal corresponding to the ambient light signal, so as to obtain the current signal corresponding to the LED optical signal.
7. The method according to claim 6, characterized in that, The calibration phase and the detection phase are alternately controlled by a periodically switching chopper control signal.
8. The method according to claim 6, characterized in that, Generating a compensation current via the compensation control signal includes: The compensation control signal controls a controlled current source to generate a first control current; the controlled current source is a PMOS current source. The compensation current is obtained based on the difference between the first control current and a bias current.
9. The method according to claim 8, characterized in that, During the calibration phase, a fixed bias current is provided to the controlled current source to provide a compensation reference when the ambient photocurrent is below a threshold.
10. A light detection system, characterized in that, The device includes a light detection sensor as described in any one of claims 1-5, an LED load, and a control switch, wherein the control switch is used to control the light emission timing of the LED load so that the light detection sensor receives an ambient light signal or an LED light signal and an ambient light signal.