A proximity light detection sensor with adaptive ambient light cancellation

Abstract

The invention discloses a proximity light detection sensor with adaptive ambient light elimination, belonging to the technical field of light detection sensors. The light detection sensor comprises: a photodiode, a transimpedance amplifier TIA, a filter, an integrator, an operational amplifier AMP3, a current conduction tube MP0 and an analog-to-digital converter ADC. The invention can effectively eliminate the external ambient light interference of the proximity light detection sensor, and compared with the method of eliminating the ambient light interference by two ADC conversions, the circuit power consumption can be significantly reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of light detection sensors, and in particular, relates to a proximity light detection sensor capable of adaptively eliminating ambient light. Background Art

[0002] In the field of mobile phones and tablets, high-performance optical sensor chips are used as standard configuration for proximity light detection. Designers can automatically adjust the brightness of the display screen according to the distance between the display screen and the object being detected, thereby reducing system power consumption. In actual under-screen application scenarios, due to the attenuation of infrared light by the display screen and the requirements of the screen on the LED light, the proximity light detection sensor needs to be able to distinguish weak infrared reflection signals of objects.

[0003] In actual applications, due to the influence of the external ambient light of the mobile phone on the optical path of the optical sensor chip, the ambient light interference will cause sensor output deviation, thereby affecting the optical sensor chip's judgment of the proximity state of the object being measured. The existing technical solution uses an adaptive elimination method to reduce the influence of ambient light interference. The typical proximity light detection system in the prior art is as follows: Figure 1 As shown, it consists of an LED transmitting end and a proximity light detection receiving end. The LED light is controlled by controlling the on and off of the LED switch SW. When the photodiode photo diode receives the ambient light and the proximity light reflection signal, the light signal is converted into an electrical signal by the analog front end AFE, and then converted into a digital signal Data by the analog-to-digital converter ADC for system-level digital signal processing. The existing technical solution eliminates the ambient light interference through the difference between two ADC conversions. The first ADC conversion is to the ambient light signal DATA1, and the second ADC conversion is to the ambient light plus proximity light signal DATA2. The ambient light interference is eliminated by converting the difference DATA2-DATA1. If the ambient light changes during the two ADC conversions, the ambient light cannot be completely eliminated, and the two ADC conversion circuits consume a large amount of power. Summary of the invention

[0004] The purpose of the present invention is to provide a proximity light detection sensor with adaptive ambient light elimination, so as to solve the problem that in the prior art, the ambient light interference is eliminated by the difference of two ADC conversions, and if the ambient light changes during the two ADC conversions, the ambient light cannot be completely eliminated, and the power consumption of the two ADC conversion circuits is large.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] A proximity light detection sensor with adaptive ambient light elimination comprises a photodiode, a transimpedance amplifier TIA, a filter, an integrator, an operational amplifier AMP3, a current conduction tube MP0 and an analog-to-digital converter ADC;

[0007] The photodiode output is connected to a transimpedance amplifier TIA composed of a feedback resistor Rf and an operational amplifier AMP1;

[0008] The output of the transimpedance amplifier TIA is connected to a DC low-pass filter composed of a MOS resistor MP1 and a filter capacitor C1;

[0009] The filter output is connected to an integrator consisting of an operational amplifier AMP2, a MOS resistor MP2 and an integrating capacitor C2;

[0010] The output of the integrator is connected to an operational amplifier AMP3, and the operational amplifier AMP3 controls the current conduction tube MP0 to generate a compensation current Icomp.

[0011] Furthermore, the transimpedance amplifier TIA is connected in parallel with a compensation resistor Rz and a compensation capacitor Cz, and the compensation resistor Rz and the compensation capacitor Cz generate a zero point.

[0012] Furthermore, the working method of the above light detection sensor is:

[0013] The photodiode converts the received DC ambient light and AC proximity light into a photocurrent signal Iamb and a photocurrent signal Iled respectively;

[0014] The transimpedance amplifier TIA converts the photocurrent signal Iamb and the photocurrent signal Iled formed by the photodiode into a voltage signal V1, wherein V1 includes a DC ambient light voltage signal and an AC proximity light voltage signal;

[0015] The filter removes the AC close to light voltage signal in the voltage signal V1 and outputs a voltage signal V2;

[0016] The integrator provides a low frequency high gain loop to eliminate ambient light interference caused at the output of the transimpedance amplifier TIA;

[0017] The operational amplifier AMP3 increases the loop gain of the system and converts the differential output of the integrator into a single-ended output voltage V3 to control the current conduction tube MP0 to generate the compensation current Icomp.

[0018] Beneficial effects of the present invention:

[0019] The present invention can effectively eliminate the external ambient light interference of the proximity light detection sensor, and compared with the method of eliminating the ambient light interference by performing two ADC conversions, it can significantly reduce the power consumption of the circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention will be further described below in conjunction with the accompanying drawings.

[0021] Figure 1It is a schematic diagram of the structure of a typical proximity light detection system in the prior art;

[0022] Figure 2 A schematic diagram of the structure of a proximity light detection sensor with adaptive ambient light cancellation;

[0023] Figure 3 It is a simulation comparison diagram of the light detection sensor of the present invention. DETAILED DESCRIPTION

[0024] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] A proximity light detection sensor with adaptive ambient light cancellation, such as Figure 2 As shown, it includes: a photodiode, a transimpedance amplifier TIA, a filter, an integrator, an operational amplifier AMP3, a current conduction tube MP0 and an analog-to-digital converter ADC;

[0026] A photodiode (Photo diode), wherein the photodiode converts the received DC ambient light and AC proximity light into a photocurrent signal Iamb and a photocurrent signal Iled respectively; the output of the photodiode is connected to a transimpedance amplifier TIA;

[0027] A transimpedance amplifier TIA, the transimpedance amplifier TIA is composed of a feedback resistor Rf and an operational amplifier AMP1, and the transimpedance amplifier TIA is used to convert the photocurrent signal Iamb and the photocurrent signal Iled formed by the photodiode into a voltage signal V1, wherein V1 includes a DC ambient light voltage signal and an AC proximity light voltage signal; the output of the transimpedance amplifier TIA is connected to a DC low-pass filter;

[0028] A filter, the filter is composed of a MOS resistor MP1 and a filter capacitor C1, and the filter is used to filter the voltage signal V1. The filter filters out the AC near-light voltage signal in the voltage signal V1, retains the DC ambient light voltage signal in V1, and outputs a voltage signal V2; the filter output is connected to an integrator;

[0029] An integrator, the integrator is composed of an operational amplifier AMP2, a MOS resistor MP2 and an integral capacitor C2, and the integrator provides a low-frequency high-gain loop to ensure that the current Icomp generated by the current-conducting tube MP0 can accurately compensate for the ambient light current Iamb to eliminate the ambient light interference caused by the output of the transimpedance amplifier TIA;

[0030] The operational amplifier AMP3 increases the loop gain of the system and converts the differential output of the integrator into a single-ended output voltage V3 to control the current conduction tube MP0 to generate the compensation current Icomp.

[0031] In addition, in order to improve the loop stability of the entire system, the transimpedance amplifier TIA is connected in parallel with a compensation resistor Rz and a compensation capacitor Cz, and the compensation resistor Rz and the compensation capacitor Cz generate a zero point to improve the loop stability.

[0032] Figure 3 For the simulation comparison of the present invention, the circuit input is 100nA DC Iamb and 0-50nA AC Iled, and the transimpedance amplifier TIA feedback resistor Rz is 4Mohm.

[0033] The red waveform is the output of the transimpedance amplifier TIA without ambient light elimination, and the output has 400mV of ambient light voltage interference. The purple waveform is the output of the transimpedance amplifier TIA after ambient light elimination, and the output voltage center value is 0V. The ambient light interference is well eliminated.

[0034] The measured ambient light interference in the 16-bit analog-to-digital converter ADC output CODE is reduced from 3000LSB to 10LSB.

[0035] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the invention or exceed the scope defined by the claims, they shall all fall within the protection scope of the present invention.

Claims

1. A proximity light detection sensor with adaptive ambient light cancellation, characterized in that: It includes a photodiode, a transimpedance amplifier TIA, a filter, an integrator, an operational amplifier AMP3, a current conduction tube MP0 and an analog-to-digital converter ADC; The photodiode output is connected to a transimpedance amplifier TIA composed of a feedback resistor Rf and an operational amplifier AMP1; The output of the transimpedance amplifier TIA is connected to a DC low-pass filter composed of a MOS resistor MP1 and a filter capacitor C1; The filter output is connected to an integrator consisting of an operational amplifier AMP2, a MOS resistor MP2 and an integrating capacitor C2; The integrator output is connected to an operational amplifier AMP3, which controls the current conduction tube MP0 to generate a compensation current Icomp; The working method of the light detection sensor is: The photodiode converts the received DC ambient light and AC proximity light into a photocurrent signal Iamb and a photocurrent signal Iled respectively; The transimpedance amplifier TIA converts the photocurrent signal Iamb and the photocurrent signal Iled formed by the photodiode into a voltage signal V1, wherein V1 includes a DC ambient light voltage signal and an AC proximity light voltage signal; The filter removes the AC close to light voltage signal in the voltage signal V1 and outputs a voltage signal V2; The integrator provides a low frequency high gain loop to eliminate ambient light interference caused at the output of the transimpedance amplifier TIA; The operational amplifier AMP3 increases the loop gain of the system and converts the differential output of the integrator into a single-ended output voltage V3 to control the current conduction tube MP0 to generate the compensation current Icomp.

2. The proximity light detection sensor with adaptive ambient light cancellation according to claim 1, characterized in that: The transimpedance amplifier TIA is connected in parallel with a compensation resistor Rz and a compensation capacitor Cz, and the compensation resistor Rz and the compensation capacitor Cz generate a zero point.

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