Self-adaptive ambient light elimination proximity light detection sensorTechnical Field
The invention belongs to the technical field of light detection sensors, and particularly relates to a self-adaptive ambient light elimination proximity light detection sensor.
Background
In the field of mobile phones and tablet computers, a high-performance optical sensor chip is used as standard configuration for proximity light detection, and a designer can automatically adjust the on-off of a display screen according to the distance between the display screen and a measured object, so that the power consumption of the system is reduced. In an actual under-screen application scene, due to the attenuation of the display screen to infrared rays and the requirement of the screen to the starting time of the LED lamp, the proximity light detection sensor is required to be capable of distinguishing weak infrared reflection signals of objects.
In practical application, because of the influence of the external environment light of the mobile phone on the light path of the optical sensor chip, the sensor output deviation can be caused by the interference of the environment light, so that the optical sensor chip is influenced to judge the approaching and distant state of the measured object. The prior art scheme reduces the influence of ambient light interference by a self-adaptive elimination method, and a typical proximity light detection system in the prior art is shown in fig. 1 and consists of an LED transmitting end and a proximity light detection receiving end. The LED lamp is controlled to emit light by controlling the on and off of the LED switch SW, and when the photodiode receives the ambient light and the near light reflection signal, the light signal is converted into an electric signal by the analog front end AFE, and then is converted into a digital signal Data by the analog-to-digital converter ADC for system digital signal processing. In the prior art, ambient light interference is eliminated through the difference value of two ADC conversions, the ambient light signal DATA1 is converted by the first ADC, the ambient light is converted by the second ADC and is adjacent to the light signal DATA2, the ambient light interference is eliminated through converting the difference value DATA2-DATA1, the ambient light cannot be completely eliminated if the ambient light changes in the two ADC conversion processes, and the power consumption of the two ADC conversion circuits is larger.
Disclosure of Invention
The invention aims to provide a self-adaptive ambient light elimination proximity light detection sensor, which solves the problems that in the prior art, ambient light cannot be completely eliminated if the ambient light changes in the two ADC conversion processes in a mode of eliminating ambient light interference through a difference value of the two ADC conversions, and the power consumption of a two ADC conversion circuit is larger.
The aim of the invention can be achieved by the following technical scheme:
The self-adaptive ambient light elimination proximity light detection sensor comprises a photodiode, a transimpedance amplifier TIA, a filter, an integrator, an operational amplifier AMP3, a current conducting pipe MP0 and an analog-to-digital converter ADC;
the photodiode output is connected with a transimpedance amplifier TIA consisting of a feedback resistor Rf and an operational amplifier AMP 1;
the TIA output of the transimpedance amplifier is connected with a direct-current low-pass filter consisting of a MOS resistor MP1 and a filter capacitor C1;
the output of the filter is connected with 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, and the operational amplifier AMP3 controls the current conduction pipe MP0 to generate the compensation current Icomp.
Further, 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.
Further, the working method of the light detection sensor comprises the following steps:
The photodiode converts the received direct current ambient light and alternating current proximity light into a photocurrent signal Iamb and a photocurrent signal Iled respectively;
the transimpedance amplifier TIA converts a photocurrent signal Iamb formed by converting a photodiode and a photocurrent signal Iled into a voltage signal V1, wherein V1 comprises a direct current environment photovoltage signal and an alternating current near photovoltage signal;
the filter filters an Alternating Current (AC) near-photovoltage signal in the voltage signal V1 and outputs a voltage signal V2;
the integrator provides a low-frequency high-gain loop and eliminates the ambient light interference caused by TIA output of the transimpedance amplifier;
the operational amplifier AMP3 increases the system loop gain and converts the integrator differential output to a single-ended output voltage V3 to control the current-conduction pipe MP0 to generate the compensation current Icomp.
The invention has the beneficial effects that:
the invention can well eliminate the external ambient light interference close to the light detection sensor, and compared with a mode of eliminating the ambient light interference by twice ADC conversion, the invention can remarkably reduce the circuit power consumption.
Drawings
The invention is further described below with reference to the accompanying drawings.
FIG. 1 is a schematic diagram of a typical proximity light detection system of the prior art;
FIG. 2 is a schematic diagram of a configuration of an adaptive ambient light canceling proximity light detection sensor;
Fig. 3 is a comparative simulation diagram of the light detection sensor of the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
An adaptive ambient light canceling proximity light detection sensor, as shown in FIG. 2, comprises a photodiode Photo diode, a transimpedance amplifier TIA, a filter, an integrator, an operational amplifier AMP3, a current conduction pipe MP0 and an analog-to-digital converter ADC;
A photodiode (Photo diode) for converting the received direct current ambient light and alternating current proximity light into a photocurrent signal Iamb and a photocurrent signal Iled, respectively, wherein the photodiode output is connected with a transimpedance amplifier TIA;
The transimpedance amplifier TIA consists of a feedback resistor Rf and an operational amplifier AMP1, and is used for converting a photocurrent signal Iamb formed by the conversion of a photodiode and a photocurrent signal Iled into a voltage signal V1, wherein V1 comprises a direct-current environment photovoltage signal and an alternating-current near photovoltage signal;
the filter is composed of an MOS resistor MP1 and a filter capacitor C1, is used for filtering a voltage signal V1, filters an alternating current near photovoltage signal in the voltage signal V1, retains a direct current environment photovoltage signal in the voltage signal V1 and outputs a voltage signal V2, and the output of the filter is connected with an integrator;
the integrator consists of an operational amplifier AMP2, a MOS resistor MP2 and an integrating capacitor C2, and provides a low-frequency high-gain loop to ensure that current Icomp generated by a current conducting pipe MP0 can accurately compensate an ambient photocurrent Iamb so as to eliminate ambient light interference caused by the output of a transimpedance amplifier TIA;
the operational amplifier AMP3 increases the system loop gain and converts the integrator differential output to a single-ended output voltage V3 to control the current-conduction pipe MP0 to generate the compensation current Icomp.
In addition, in order to improve the loop stability of the whole system, the transimpedance amplifier TIA is connected in parallel with the compensation resistor Rz and the compensation capacitor Cz, and the compensation resistor Rz and the compensation capacitor Cz generate a zero point to improve the loop stability.
FIG. 3 shows a simulation comparison of the invention, wherein the circuit inputs are 100nA DC Iamb and 0-50 nA AC Iled, and the TIA feedback resistance Rz of the transimpedance amplifier is 4Mohm.
The red waveform is output by the transimpedance amplifier TIA which does not perform ambient light cancellation, 400mV ambient light voltage interference is output, the purple waveform is output by the transimpedance amplifier TIA which performs ambient light cancellation, the output voltage center value is 0V, and the ambient light interference is well cancelled.
The ambient light interference in the output CODE of the measured 16bit analog to digital converter ADC is reduced from 3000LSB to 10LSB.
The foregoing is merely illustrative and explanatory of the invention, as various modifications and additions may be made to the particular embodiments described, or in a similar manner, by those skilled in the art, without departing from the scope of the invention or exceeding the scope of the invention as defined in the claims.