CN101158590A - Device and method for fully digital four-quadrant detector detecting laser beam deflection angle - Google Patents

Abstract

The invention relates to a device and a method for detecting the deflection angle of a laser beam by a fully digital four-quadrant detector. The device has a preamplifier circuit (12), a filter circuit (13), an AD conversion circuit (16), an offset display module (18), a four-quadrant detector (1), a secondary amplifier circuit module (14 ), a variable gain amplifier circuit module (15) and a high-speed microprocessor module (17); the present invention solves the problem that measurement accuracy decreases due to the adoption of an all-digital processing method; adopts an adaptive variable gain amplifier circuit to make the The method can maintain the signal strength when it enters the AD acquisition unit by automatically changing the gain according to the strength of the input signal, and overcomes the shortcomings of the reduction of the resolution accuracy caused by the decrease of the signal-to-noise ratio caused by the change of the input light intensity; Using a high-speed microprocessor to calculate the beam deflection angle overcomes the disadvantage of slow calculation speed caused by the use of a single-chip computer.

Description

Device and method for fully digital four-quadrant detector detecting laser beam deflection angle

technical field

The invention belongs to the technical field of photoelectric measurement, and relates to a device and a method for detecting the deflection angle of a laser beam by an all-digital four-quadrant detector.

Background technique

At present, the photodetectors mainly used to measure the deflection angle of the laser beam include charge-coupled device (CCD), position sensor (PSD) and four-quadrant detector (QD). Although the data output by the charge-coupled device (CCD) can directly reflect the position of the light spot on the photosensitive surface, and then obtain the deflection angle of the laser beam (relative to the optical axis) according to its offset relative to the center of the photosensitive surface, but the charge-coupled There are too many pixels in the device (CCD), and the amount of data to be processed is too large, which is not suitable for the measurement of the laser beam deflection angle with a high dynamic range; while the position sensor (PSD), its data processing is relatively low compared to the charge-coupled device (CCD). The language is much simpler, but due to the parametric characteristics of the device itself, its performance is not as good as that of QD. At the same time, QD is also widely used in the fields of boresight alignment, angle measurement and tracking.

In the patent "a device and method for detecting the swing attitude of a plane mirror" (Chinese patent application, publication number: CN1487264A.), a four-quadrant detector is used as its photoelectric sensor, and its processing circuit is shown in Figure 4. It consists of 21 preamplifier circuit modules, 22 sum difference circuit modules, 23 phase lock detection circuit modules, 24 filter circuit modules, 25AD conversion circuit modules, 26 single-chip microcomputers and 27 measurement result units. After the four channels of the four-quadrant detector pass through the preamplifier circuit, the sum and difference are calculated, and then through the phase-locking detection method, the signal is extracted for AD conversion, and the converted data is sent to the single-chip computer for offset calculation. Finally, the single-chip microcomputer sends the calculation result to the upper computer for display through the RS485 interface. Because it uses a sum-difference circuit, it will cause crosstalk between the four-way signals of the four-quadrant detector and introduce additional common-mode noise, and it is not convenient to compensate the unbalanced performance between channels through software, reducing the resolution accuracy ; Because it uses a single-chip microcomputer, its calculation accuracy and calculation speed are limited. In this system, the fastest speed is 90 times/S.

Contents of the invention

The invention mainly aims to solve the deficiency of spot offset calculation speed and calculation accuracy in QD detection of laser beam deflection angle, and provides a fully digital four-quadrant detector for detecting laser beam deflection angle device and implementation method.

The basic idea of the present invention is as follows: the laser beam is imaged onto the photosensitive surface of the QD sensor through the imaging objective lens unit, and the optical signal is converted into an electrical signal by the QD sensor. Perform filtering, then perform secondary amplification and adaptive variable gain amplification on the filtered signal, and then send it to the AD conversion circuit, then send the AD converted signal to a high-speed microprocessor for spot offset calculation, and finally The calculated laser beam offset angle is displayed.

As shown in Figure 3, the device for detecting the deflection angle of the laser beam by a fully digital four-quadrant detector consists of a four-quadrant detector 1, a preamplifier circuit module 12, a filter circuit module 13, a secondary amplifier circuit module 14, a variable A gain amplifier circuit module 15, an AD conversion module 16, a high-speed microprocessor module 17 and an offset display module 18 form;

Preamplifier circuit module 12, filter circuit module 13, secondary amplifier circuit module 14, variable gain amplifier circuit module 15, AD conversion module 16, high-speed microprocessor module 17 and offset display module 18 are connected in sequence, and the high-speed microprocessor The processor module 17 is also connected to the variable gain amplifier circuit module 15 .

Compared with the prior art "A device and method for detecting the swing posture of a plane mirror", the present invention adopts a 1. Adaptive variable gain amplifier circuit module 15, used to ensure a better signal-to-noise ratio when the incident laser light power is unstable, so as to improve the calculation accuracy of deflection angle; 2. High-speed microprocessor 17, It is used to replace the single-chip microcomputer for data calculation, and can achieve higher calculation accuracy and calculation speed when performing digital signal processing; 3. The sum and difference circuit and phase-lock detection are not used, and the connection position of the filter circuit is adjusted. , so that noise can be better suppressed; a high-speed microprocessor 17 is used to replace the single-chip microcomputer, so that higher resolution accuracy and resolution speed can be achieved when digital signal processing is performed.

Provide a fully digital four-quadrant detector method for detecting the deflection angle of the laser beam, the steps and conditions are as follows:

(1) Adjust the position of the photosensitive surface of the QD photodetector relative to the imaging objective lens unit 2 to adjust the size of the imaging spot on the QD photosensitive surface:

As shown in Figure 1, the laser beam is focused onto the QD photodetector 1 through the imaging objective lens unit 2, and the position of the photosensitive surface of the QD photodetector relative to the imaging objective lens unit 2 needs to be adjusted to make the imaging on the photosensitive surface of the QD photodetector The size of the light spot 3 can be adjusted within 0.1 times to 1 times the diameter of the inscribed circle on the photosensitive surface of the QD photodetector, so as to achieve the best detection performance.

(2) Measure the photocurrent generated by the imaging spot in the four quadrants of the QD photodetector:

As shown in Figure 2, the imaging spot 3 after the laser beam passes through the imaging objective lens unit 2 is located in four quadrants of the photosensitive surface 2 of the QD photodetector 1: the first quadrant 4, the second quadrant 5, the third quadrant 6 and the fourth quadrant. In quadrant 7, QD photodetector 1 converts the light energy in each quadrant into corresponding current, because the photocurrent is proportional to the light power incident on the corresponding photosensitive surface, and the light power is in turn proportional to the imaging light spot on QD detector 4. The area occupied by each quadrant is related to the energy distribution of the spot. When the spot energy distribution is uniform, the quadrant current is proportional to the spot area occupied by the quadrant. That is, the imaging spot can be obtained by measuring the current generated by the four quadrants. Relative to the coordinates of the coordinate system formed by the four quadrants of the four-quadrant detector, the deflection angle of the laser beam can be obtained.

Because the spectral line width of the laser is very narrow, relative to the spectral response curve of the QD photodetector 1, the laser source can be considered as a line light source, that is, the responsivity of the QD photodetector is constant within the laser beam band range, then The response current of each quadrant of the QD photodetector is proportional to the magnitude of the light power obtained by the quadrant. Due to the different distribution of the light energy of the imaging spot 3 in the four quadrants, the magnitude of the current converted by the QD photodetector 1 in each quadrant is also different. They directly reflect the position of the spot energy center relative to the coordinate system formed by the four quadrants of the image sensitive surface of the QD photodetector, and the deflection angle of the laser beam can be obtained from this position.

(3) Convert the current signal generated by the four-quadrant photodetector into a voltage signal and amplify it:

As shown in Figure 3, the QD photodetector 1 converts the imaging spot 3 corresponding to the light energy and the position information of the spot on the four quadrants of the QD photodetector into corresponding four-way electrical signals after the laser beam passes through the imaging objective lens unit 2 : The current obtained in the first quadrant is 8, let it be I1; the current obtained in the second quadrant is 9, let it be I2; the current obtained in the third quadrant is 10, let it be I3; the photocurrent obtained in the fourth quadrant is 11, let it be I4. These four current signals are converted into voltage signals by the preamplifier circuit module 12 and amplified.

The pre-amplification circuit module 12 has the following three implementation methods: (1) The current signals obtained by the QD photodetector: I1, I2, I3, and I4 are directly converted into voltage signals by zero-bias amplification, and simultaneously amplified ; (2) Let the QD photodetector work under the working state of the reverse bias voltage, adopt the form of DC amplification to convert the current signal obtained by the QD photodetector: I1, I2, I3, I4 into a voltage signal, and make it Amplify; (3) Let the QD photodetector work under the working state of reverse bias voltage, and convert the current signals obtained by the QD photodetector: I1, I2, I3, I4 into voltage signals U1, U2 in the form of AC amplification , U3, U4, and enlarge them.

(4) The filtering circuit module 13 is adopted, which is an inventive point of the present invention. Adding the filter circuit module 13 here can suppress noise better than that added after phase-locking detection in "A device and method for detecting swing attitude of a plane mirror" (Chinese patent application, publication number: CN1487264A).

Adopt filtering circuit module 13 to carry out filtering to the preamplified voltage signal U1, U2, U3, U4 that step (3) obtains and improve signal-to-noise ratio:

Adopt filter circuit module 13 to filter the preamplified voltage signals U1, U2, U3, U4 obtained in step (3), obtain signals UL1, UL2, UL3, UL4, improve the signal-to-noise ratio, according to the frequency band of the optical signal and Application requirements can design a specific filter circuit to achieve the best filtering effect, improve the signal-to-noise ratio, and improve the calculation accuracy of the spot offset.

Therefore, it is due to the inherent noise of the QD photodetector, the inherent noise of the preamplifier circuit, background noise and other noises, resulting in a low signal-to-noise ratio of the preamplified signal.

(5) The secondary amplifying circuit module 14 is used to re-amplify the filtered signals UL1, UL2, UL3, and UL4 to increase the amplitude of the effective signal and improve the signal-to-noise ratio. This is an inventive point of the present invention. The secondary amplification of the signal is to achieve impedance matching with the filter circuit module; the other is to reduce the performance requirements of the preamplifier.

Since the signal is usually very weak in the measurement of the long-distance laser beam deflection angle, although the signal is enhanced after passing through the pre-amplification circuit, it is still very small, and it needs to be amplified again. The present invention uses the secondary amplifying circuit module 14 to re-amplify the filtered signal to obtain signals US1, US2, US3 and US4, thereby increasing the amplitude of the effective signal and improving the signal-to-noise ratio.

(6) Adaptive variable gain amplifier circuit module 15 is adopted, which is an inventive point of the present invention. The adoption of the module can change the amplification factor according to the strength of the current signal, so that the amplitude of the amplified signal can be kept at a high level, and the detection accuracy can be improved.

An adaptive variable gain amplifier circuit is used to keep the signal-to-noise ratio at a high level, ensuring the stability of the accuracy of spot offset calculation:

Due to the long transmission distance, it is inevitable to be interfered by other factors during the transmission process, resulting in a decrease in signal strength. In the case of the same amplification factor, the signal-to-noise ratio of the signal is reduced, resulting in a decrease in the accuracy of offset calculation. The present invention adopts adaptive variable gain amplifier circuit module 15 to process signals US1, US2, US3, US4 (increase the amplification factor when the signal is weak, reduce the amplification factor when the signal is too strong), and obtain signals UA1, UA2 , UA3, UA4.

(7) After carrying out variable gain amplification to the signal, adopt four-way AD conversion circuit 16 to convert the analog signal into a digital signal:

After the signals are amplified with variable gain, the AD conversion module 16 is used to convert the four analog signals UA1 , UA2 , UA3 , UA4 into four serial digital signals ADC1 , ADC2 , ADC3 , ADC4 . In the four-way AD conversion circuit 16, an appropriate AD converter can be selected according to the required conversion precision, the range of the signal voltage, the number of channels, the conversion mode (synchronous conversion or sequential conversion) of the channel AD conversion, etc. Each channel can be sampled at the same time and be independent from each other to reduce the mutual interference between channels, and select the number of AD converters required. In this module, it is also necessary to process the output signal of the adaptive variable gain amplifier circuit module 15 to meet the performance requirements of the input signal of the AD converter and achieve the best AD conversion performance.

(8) Adopt high-speed microprocessor 17, this is an inventive point of the present invention. After the analog-to-digital conversion is carried out to the four-way analog signals, the digital signals obtained after the conversion are output to the high-speed microprocessor 17 for processing:

After analog-to-digital conversion is performed on the signal, the converted digital signal is output to the high-speed microprocessor 17 for processing. In this module, it is necessary to complete the digital filtering processing of the four-channel digital signals ADC1, ADC2, ADC3, and ADC4, to compensate the non-uniformity of the four quadrants of the QD photodetector and the non-uniformity between the four channels of the subsequent processing circuit, etc., automatically Adapt to the control of the magnification of the variable gain amplifier circuit module 15, the calculation of the offset of the light spot on the QD photoelectric sensor, the calculation of the deflection angle of the laser beam, and the transmission of the offset. Due to the high computing speed of high-speed microprocessors (such as: DSP, FPGA, etc.), which can reach tens of megabytes, hundreds of megabytes or even gigabytes, and the computing precision of such high-speed microprocessors is also very high, most of them can More than 16 bits, almost all of which are greater than the processing speed and processing accuracy of the single-chip microcomputer, so these tasks can be completed quickly, and the laser beam deflection angle can be obtained, so as to achieve a very high beam deflection angle calculation speed, and at the same time improve the calculation of the beam deflection angle precision.

(9) The offset display module 18 is adopted, which is convenient for human eyes to observe. The present invention uses an offset display module 18 to display the deflection angle information of the laser beam. The display module can receive the laser beam deflection angle calculated by the high-speed microprocessor module by the host computer, and then display it on the host computer; it can also be displayed by another MCU through a digital tube, a liquid crystal display or other display devices. The deflection angle of the laser beam.

Effect of the present invention: the present invention can overcome the shortcoming that the measurement accuracy reduces due to the unbalanced performance parameters between the channels of the analog circuit of the pre-stage signal conditioning due to the adoption of the full digital processing method; The reduction of the solution accuracy caused by the influence of the circuit common mode voltage, offset voltage, etc.; and because of the use of an adaptive variable gain amplifier circuit, the method can automatically change the gain according to the strength of the input signal to maintain access to AD The size of the signal strength at the time of the acquisition unit overcomes the shortcomings of the reduction of the resolution accuracy caused by the decrease of the signal-to-noise ratio caused by the change of the input light intensity; The disadvantage of slow solution speed caused by single-chip computer solution.

Description of drawings

Figure 1 is a diagram of the optical path for measuring the deviation angle of the laser beam. 1 in Figure 1 represents the photosensitive surface of the QD. 2 is the imaging objective lens unit 2.

Fig. 2 is a schematic diagram of the light spot on the photosensitive surface of the QD detector. In Figure 2, 1 is the QD photodetector, 2 is the imaging objective lens unit 2, 3 is the imaging spot 3, 4 is the first quadrant 4, 5 is the second quadrant, 6 is the third quadrant 6, 7 is the fourth quadrant 7.

Fig. 3 is a structural block diagram of a fully digital four-quadrant detector for detecting the deflection angle of a laser beam. This figure is also an abstract drawing.

In Fig. 3, 2 is the imaging objective lens, 3 is the imaging spot 3, 8 is the current 8 obtained in the first quadrant, let it be I1, 9 is the current 9 obtained in the second quadrant, let it be I2, and 10 is the obtained current 10 in the third quadrant , let it be I3; 11 is the photocurrent 11 obtained in the fourth quadrant, let it be I4.

Fig. 4 is a processing circuit diagram of a photoelectric sensor using a four-quadrant detector in the prior art.

Fig. 5 is a circuit diagram of the first quadrant of the four-quadrant detector preamplifier circuit.

Fig. 6 is a circuit diagram of the first quadrant filter circuit of the four-quadrant detector.

Fig. 7 is a circuit diagram of the secondary amplifier circuit of the first quadrant of the four-quadrant detector.

Detailed ways

Example 1

The circuit diagram of the analog circuit is given. Since the adaptive variable gain amplifier circuit, AD conversion circuit and microprocessor circuit can be directly designed in the application circuit in the datasheet of the device, the analog circuit is the core of the real circuit, so Only the circuit diagram of the analog part is given.

As shown in Figure 3, a fully digital device for detecting the deflection angle of a laser beam consists of: a QD photodetector 1, a preamplifier circuit module 12, a filter circuit module 13, a secondary amplifier circuit module 14, an adaptive Variable gain amplification circuit module 15, four-way AD conversion circuit 16, high-speed microprocessor 17 and offset display module 18 constitute;

Preamplifier circuit module 12, filter circuit module 13, secondary amplifier circuit module 14, variable gain amplifier circuit module 15, AD conversion module 16, high-speed microprocessor module 17 and offset display module 18 are connected in sequence; The processor module 17 is also connected to the variable gain amplifier circuit module 15 .

Below in conjunction with accompanying drawing, provide the method that fully digitized four-quadrant detector detects the deflection angle of laser beam, its steps and conditions are as follows:

In Fig. 1, the laser beam is focused on the photosensitive surface 1 of the QD photodetector through the imaging objective lens unit 2. The size of the imaging light spot on the photosensitive surface of the device can be adjusted within the range of 0.1 times to 1 times the diameter of the inscribed circle on the photosensitive surface of the QD photodetector, so as to achieve the best detection performance.

In Fig. 2, the imaging spot 3 after the laser beam passes through the imaging objective lens 2 is located in four quadrants of the photosensitive surface 2 of the QD photodetector 1: the first quadrant 4, the second quadrant 5, the third quadrant 6 and the fourth quadrant 7 In , when the QD photodetector converts the light energy in each quadrant into the corresponding current, since the light energy of the imaging spot 3 has different components in the four quadrants, the light energy of each quadrant converted by the QD photodetector The magnitude of the current is also different, because the spectral line width of the laser is very narrow. Compared with the spectral response curve of the QD photodetector, the laser source can be considered as a line light source, that is, the responsivity of the QD photodetector is within the range of the laser beam band. The inside is a constant, then the response current of each quadrant of the QD photodetector is proportional to the magnitude of the optical power obtained by the quadrant. They directly reflect the position of the spot energy center relative to the coordinate system formed by the four quadrants of the image sensitive surface of the QD photodetector, and the deflection angle of the laser beam can be obtained from this position.

In Figure 3, the QD photodetector converts the imaging spot 3 corresponding to the light energy and spot position information on the four quadrants of the QD detector after the laser beam passes through the imaging objective lens 2 into corresponding four-way electrical signals: the first quadrant The obtained current 8, let it be I1; the second quadrant obtained current 9, let it be I2; the third quadrant obtained current 10, let it be I3; the fourth quadrant obtained photocurrent 11, let it be I4. These four current signals are converted into voltage signals by the pre-amplification circuit module and amplified.

The pre-amplification circuit module 12 has the following three implementations: (1) adopt zero-bias amplification to directly convert the current signals (I1, I2, I3, I4) obtained by the QD photodetector into voltage signals, and at the same time make it obtain Amplify; (2) Let the QD photodetector work under the working state of reverse bias voltage, adopt the form of DC amplification to convert the current signal (I1, I2, I3, I4) obtained by the QD photodetector into a voltage signal, and Make it amplified; (3) Let the QD photodetector work under the working state of the directional bias, adopt the form of AC amplification to convert the current signal (I1, I2, I3, I4) obtained by the QD photodetector into a voltage signal, and make it bigger. If the second implementation can be adopted, the preamplifier circuit takes the first quadrant as an example, as shown in FIG. 5 .

Due to the inherent noise of the QD photodetector, the inherent noise of the pre-amplification circuit, background noise and other noises, the signal-to-noise ratio of the pre-amplified signal is low. In the present invention, the filter circuit module 13 is used to filter it, so as to improve the signal-to-noise ratio. According to the frequency band of the optical signal and application requirements, a specific filter circuit can be designed to achieve the best filtering effect, improve the signal-to-noise ratio, and improve the calculation accuracy of the spot offset. Taking the first quadrant as an example, the filter circuit can be designed as shown in Figure 6. Since the signal is usually very weak in the measurement of the long-distance laser beam deflection angle, although the signal is enhanced after passing through the pre-amplification circuit, it is still very small, and it needs to be amplified again. The present invention uses the secondary amplifying circuit module 14 to re-amplify the filtered signal to increase the amplitude of the effective signal and improve the signal-to-noise ratio. Taking the first quadrant as an example, the secondary amplifier circuit can be shown in FIG. 7 .

At the same time, due to the long transmission distance, other factors will inevitably be interfered during the transmission process, resulting in a decrease in signal strength. In the case of the same amplification factor, the signal-to-noise ratio of the signal is reduced, resulting in a decrease in the accuracy of offset calculation. The present invention adopts adaptive variable gain amplifier circuit module 15 to process it, increases the amplification factor when the signal is weak, and reduces the amplification factor when the signal is too strong, so that the signal-to-noise ratio remains at a high state, ensuring The stability of spot offset calculation accuracy. The circuit diagram here can be designed with reference to the Datasheet of the selected variable gain amplifier.

After the signal is amplified with variable gain, an AD conversion module 16 is used to convert the analog signal into a digital signal. In the four-way AD conversion circuit 16, an appropriate AD converter can be selected according to the required conversion precision, the range of the signal voltage, the number of channels, the conversion mode (synchronous conversion or sequential conversion) of the channel AD conversion, etc. Each channel can be sampled at the same time and be independent from each other to reduce the mutual interference between channels, and select the number of AD converters required. In this module, it is also necessary to process the output signal of the adaptive variable gain amplifier circuit module 15 to meet the performance requirements of the input signal of the AD converter and achieve the best AD conversion performance. Here, the AD converter can be single-channel, and its circuit can be designed with reference to the Datasheet of the device.

After analog-to-digital conversion is performed on the signal, the converted digital signal is output to the high-speed microprocessor 17 for offset calculation. In this module, it is necessary to complete the digital filtering process from the four channels to the digital signal, to compensate the non-uniformity of the four quadrants of the QD photodetector and the non-uniformity between the four channels of the subsequent processing circuit, etc., and the self-adaptive variable gain amplifier circuit module 15 magnification control, calculation of light spot offset on QD photoelectric sensor, calculation of laser beam deflection angle, transmission of offset, etc. Due to the high computing speed of high-speed microprocessors (such as: DSP, FPGA, etc.), it can reach tens of megabytes, hundreds of megabytes or even gigabytes. More than 16 bits, almost all of which are greater than the processing speed and processing accuracy of the single-chip microcomputer, so these tasks can be completed quickly, and the laser beam deflection angle can be obtained, so as to achieve a very high beam deflection angle calculation speed, and at the same time improve the calculation of the beam deflection angle precision.

In order to facilitate observation by human eyes, the present invention uses an offset display module 18 to display the deflection angle information of the laser beam. The display module can receive the laser beam deflection angle calculated by the high-speed microprocessor module by the host computer, and then display it on the host computer; it can also be displayed by another MCU through digital tubes, liquid crystals or other display devices to display the laser beam deflection angle.

Claims (5)

1. The device for detecting the deflection angle of the laser beam by the fully digital four-quadrant detector is characterized by comprising a pre-amplification circuit (12), a filter circuit (13), an AD conversion circuit (16) and an offset display module (18), and further comprising a four-quadrant detector (1), a secondary amplification circuit module (14), a variable gain amplification circuit module (15) and a high-speed microprocessor module (17);

the pre-amplification circuit module (12), the filter circuit module (13), the secondary amplification circuit module (14), the variable gain amplification circuit module (15), the AD conversion module (16), the high-speed microprocessor module (17) and the offset display module (18) are connected in sequence; the high-speed microprocessor module (17) is also connected with the variable gain amplifying circuit module (15).

2. The method for detecting the deflection angle of the laser beam by the fully-digitalized four-quadrant detector is characterized by comprising the following steps and conditions:

1) adjusting the position of the photosensitive surface of the four-quadrant detector (1) relative to the imaging objective unit (2) to adjust the size of the imaging light spot on the photosensitive surface of the four-quadrant detector (1):

laser beams are focused on a photosensitive surface of the four-quadrant detector (1) through the imaging objective lens unit (2), and the position of the photosensitive surface of the four-quadrant detector (1) relative to the imaging objective lens unit (2) is adjusted, so that the size of an imaging light spot (3) on the photosensitive surface of the four-quadrant detector (1) can be adjusted within a circle-joining diameter of the photosensitive surface of the four-quadrant detector (1) from 0.1 time to 1 time;

2) measuring photocurrent generated by imaging light spots in four quadrants of a four-quadrant detector (1);

3) converting the photocurrent signal into a voltage signal and amplifying it:

the four-quadrant detector (1) converts light energy of an imaging light spot (3) of a laser beam passing through the imaging objective lens unit (2) and corresponding to four quadrants of the four-quadrant detector (1) and position information of the light spot into corresponding four paths of electric signals: the current (8) obtained in the first quadrant is I1; the current (9) obtained in the second quadrant is I2; the current (10) obtained in the third quadrant is I3; the photocurrent (11) obtained in the fourth quadrant is I4, and the four paths of current signals are converted into voltage signals through the preamplification circuit module (12) and are amplified; the method comprises the following steps:

the pre-amplification circuit module (12) adopts a zero-offset amplification mode to obtain current signals from the four-quadrant detector (1): i1, I2, I3 and I4 are directly converted into voltage signals and amplified; or,

the four-quadrant detector (1) works in a reverse bias working state, and a direct current amplification form is adopted to obtain current signals of the four-quadrant detector (1): i1, I2, I3 and I4 are converted into voltage signals and amplified; or,

the four-quadrant detector (1) works in a reverse bias working state, and current signals obtained by the four-quadrant detector (1) are amplified in an alternating current mode: i1, I2, I3 and I4 are converted into voltage signals and amplified;

4) filtering the pre-amplified signal obtained in the step 3) by using a filter circuit module (13) to improve the signal-to-noise ratio;

5) adopting a secondary amplifying circuit module (14) to amplify the filtered signal of the step 4) again, increasing the amplitude of the effective signal, and improving the signal-to-noise ratio:

6) the signal obtained in the step 5) is further amplified by adopting an adaptive variable gain amplification circuit module (15), the amplification factor is increased when the signal is weak, and the amplification factor is reduced when the signal is too strong, so that the signal-to-noise ratio is kept in a high state, and the stability of the light spot offset resolving precision is ensured;

7) the signals obtained in the step 6) are converted into digital signals through a four-way AD conversion circuit (16):

in the four-way AD conversion circuit (16), the conversion voltage range of an AD conversion chip can be determined according to the amplitude range of the output signal after the self-adaptive variable gain amplification circuit module (15); the four-way AD conversion circuit can simultaneously carry out four-way AD conversion, has better integrated linear error and differential linear error, has no crosstalk as much as possible during the four-way AD conversion, and can select proper AD conversion chips and the number of the chips according to the requirements;

8) after the signals are subjected to analog-to-digital conversion, the converted digital signals are output to a high-speed microprocessor (17) for offset solution:

the control of an AD conversion chip, the digital filtering processing of four-channel digital signals of ADC1, ADC2, ADC3 and ADC4, the compensation of the nonuniformity of four quadrants of a four-quadrant detector (1) and the nonuniformity among four channels of a subsequent processing circuit, the control of the amplification factor of a self-adaptive variable gain amplification circuit module (15), the calculation of the light spot offset, the calculation of the laser beam deflection angle and the transmission of the offset of the four-quadrant detector (1) are required to be completed in the module, and the laser beam deflection angle is obtained;

9) and an offset display module (18) is adopted to display the deflection angle information of the laser beam:

the display module can receive the laser beam deflection angle calculated by the high-speed microprocessor module through an upper computer and then display the laser beam deflection angle on the upper computer; alternatively, the deflection angle of the laser beam is displayed by another microcontroller via a digital tube, liquid crystal display, or other display device.

3. The fully digitized method for detecting the deflection angle of laser beam in four-quadrant detector according to claim 2, wherein the pre-amplifying circuit module (12) in step 3) directly converts the current signals I1, I2, I3 and I4 obtained from the four-quadrant detector (1) into voltage signals by means of zero-offset amplification, and simultaneously amplifies the voltage signals.

4. The fully digitized method for detecting the deflection angle of laser beam by four-quadrant detector according to claim 2, wherein the pre-amplifying circuit module (12) in step 3) is configured to make the four-quadrant detector (1) operate under reverse-biased operating condition, and convert the current signals I1, I2, I3, I4 obtained by the four-quadrant detector (1) into voltage signals in the form of dc amplification, and amplify them.

5. The fully digitized method for detecting the deflection angle of laser beam by four-quadrant detector according to claim 2, wherein the pre-amplifying circuit module (12) in step 3) is configured to operate the four-quadrant detector (1) in reverse-biased operating state, and to convert the current signals I1, I2, I3, I4 obtained by the four-quadrant detector (1) into voltage signals in the form of ac amplification and amplify the voltage signals.

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