CN110873552B - Laser interferometer receiver - Google Patents
Laser interferometer receiver Download PDFInfo
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- CN110873552B CN110873552B CN201811012250.1A CN201811012250A CN110873552B CN 110873552 B CN110873552 B CN 110873552B CN 201811012250 A CN201811012250 A CN 201811012250A CN 110873552 B CN110873552 B CN 110873552B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B9/00—Measuring instruments characterised by the use of optical techniques
- G01B9/02—Interferometers
- G01B9/02015—Interferometers characterised by the beam path configuration
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B9/00—Measuring instruments characterised by the use of optical techniques
- G01B9/02—Interferometers
- G01B9/02055—Reduction or prevention of errors; Testing; Calibration
Abstract
The invention provides a laser interferometer receiver which comprises a photoelectric detection unit, an I/V conversion unit, a multi-channel band-pass filtering unit, an AGC unit, a phase compensation unit, a comparator, a weak signal suppression unit and a control unit. The invention can not only improve the measurement precision and the measurement efficiency, but also increase the channel number of the measurement light path, and has high signal-to-noise ratio.
Description
Technical Field
The invention relates to the technical field of measurement, in particular to a laser interferometer receiver.
Background
The double-frequency laser interferometer is a device for displacement measurement by using the optical interference principle and taking the optical wavelength as the measurement scale, has the advantages of high resolution, strong anti-interference capability, good repeatability, wide range, high speed, non-contact and the like, and is widely applied to various high-end fields needing accurate displacement measurement, such as microelectronic manufacturing, precise machine tool processing, coordinate calibration, positioning and the like. Briefly, the principle of measuring displacement by using a dual-frequency laser interferometer is as follows: if the phase of one beam is not changed, the phase change of the other beam can be detected by detecting the change of the interference fringe, and the micro displacement of the reflector is calculated by the phase change.
The optical fiber collimator and the photoelectric receiver of the early dual-frequency laser interferometer or the dual-frequency laser interferometer applied to the low-precision field are together, so that the heat dissipation of the photoelectric receiver generates disturbance to the air in a measurement area, and measurement errors are caused. The art thus proposes a specific application of separating the laser interferometer collimator and the receiver.
Referring to fig. 1, a conventional laser interferometer receiver includes a photo detector 101, a current/voltage converter (I/V converter) 102, a 0.1-10M bandpass filter 103 with fixed bandwidth frequency, an Automatic Gain Control (AGC) unit 104, a weak signal suppression unit 105, and a comparator 106. The working principle is as follows: the photodetection unit 101 (which is a photodiode) receives the interference light signal and converts it into a current signal, then the I/V conversion unit 102 converts the current signal into a voltage signal, which contains noise in a certain frequency range, and after filtering by the band-pass filter 103, extracts both the effective signal and the noise signal in the frequency range of 0.1-10M, and then amplifies them by the AGC unit 104, and the weak signal suppression unit 105 determines whether to turn off the comparator 106 according to the amplified signal amplitude, so as to determine whether to output the frequency signal. When the passband is not matched with the frequency of the input signal, the noise with low amplitude is received by the post-stage, and at this time, the weak signal suppression unit 105 turns off the comparator 106 and does not output a frequency signal; when the pass band matches the input signal frequency, the weak signal suppressing unit 105 turns on the comparator 106 so that it outputs the frequency signal f.
The laser interferometer receiver has the disadvantages that the bandwidth frequency range of the band-pass filter is too wide, so that the included noise signal is larger, the signal to noise ratio is reduced, and meanwhile, the band-pass filter is one, so that the channel of the measuring optical path is single, the multiplexing function of multiple channels cannot be realized, and the defects of reduction of the measuring efficiency and the measuring precision are caused.
Disclosure of Invention
The invention aims to provide a laser interferometer receiver to improve the measurement efficiency and the measurement precision of a light source channel.
In order to solve the above technical problem, the present invention provides a laser interferometer receiver, comprising a photoelectric detection unit for detecting an interference optical signal emitted by a laser interferometer and converting the interference optical signal into an analog current signal;
an I/V conversion unit for converting the analog current signal converted by the photoelectric detection unit into an analog voltage signal;
the multi-channel band-pass filtering unit is used for selecting a certain channel of a sub-frequency bandwidth with a narrow frequency range in a receivable frequency bandwidth so as to carry out band-pass filtering on the analog voltage signal output by the I/V conversion unit;
the AGC unit is used for amplifying the analog voltage signal subjected to band-pass filtering by the multi-channel band-pass filtering unit;
the phase compensation unit is used for compensating phase deviation caused by the analog voltage signal subjected to band-pass filtering by the multi-channel band-pass filtering unit;
the comparator is used for comparing the analog voltage signal compensated by the phase compensation unit with a preset value, and when the analog voltage signal compensated by the phase compensation unit is greater than the preset value, the comparator outputs a high level; when the analog voltage signal compensated by the phase compensation unit is smaller than a preset value, the comparator outputs a low level to convert the analog voltage signal output by the comparator into a digital voltage signal;
the weak signal suppression unit is used for judging whether to close the output of the comparator according to the amplitude of the analog voltage signal amplified by the AGC unit;
and the control unit is used for positioning and gating the channel band-pass filtering unit with a certain sub-frequency bandwidth in the multi-channel band-pass filtering unit to carry out band-pass filtering according to the current frequency value output by the comparator, and setting the phase parameter of the phase compensation unit according to the current frequency value output by the comparator so as to compensate the phase offset caused by the analog voltage signal filtered by the multi-channel band-pass filtering unit.
Furthermore, in the laser interferometer receiver provided by the invention, the multi-channel band-pass filtering unit comprises a selector switch and a plurality of multi-channel band-pass filters with different sub-frequency bandwidths, and the selector switch is used for switching on one channel in the multi-channel band-pass filters and switching off the other channels.
Further, in the laser interferometer receiver provided by the invention, the change-over switch is a multi-bit high-speed analog switch.
Further, the invention provides a laser interferometer receiver, wherein the multichannel band-pass filter comprises:
the sub-frequency bandwidth of the first channel band-pass filter is 0.1-2MHz, and the central frequency is 1 MHz;
the sub-frequency bandwidth of the second channel band-pass filter is 2-4MHz, and the central frequency is 3 MHz;
the sub-frequency bandwidth of the third channel band-pass filter is 4-6MHz, and the central frequency is 5 MHz;
the sub-frequency bandwidth of the fourth channel band-pass filter is 6-8MHz, and the central frequency of the fourth channel band-pass filter is 7 MHz;
and a fifth channel band-pass filter, wherein the sub-frequency bandwidth is 8-10MHz, and the center frequency is 9 MHz.
Further, in the laser interferometer receiver provided by the invention, any one of the multi-channel band-pass filters is an LC band-pass filter formed by an inductor L and a capacitor C which are connected in parallel.
Furthermore, the multi-channel band-pass filter unit of the laser interferometer receiver further comprises a summation unit connected behind the multi-channel band-pass filter, and the summation unit is used for superposing and denoising the gated certain channel band-pass filter and the simultaneously closed certain channel band-pass filter.
Further, in the laser interferometer receiver provided by the invention, the summing unit is an adder.
Furthermore, in the laser interferometer receiver provided by the invention, the multi-channel band-pass filtering unit is an adjustable band-pass filter.
Further, in the laser interferometer receiver provided by the invention, the adjustable band-pass filter is an LC resonance filter which is formed by connecting an inductor L1 and a varactor VD1 in parallel and can adjust the frequency bandwidth.
Further, in the laser interferometer receiver provided by the invention, the phase compensation unit is a digital potentiometer, and the control unit adjusts resistance change of the digital potentiometer according to the current frequency value output by the comparator so as to compensate phase offset generated by the analog voltage signal after band-pass filtering.
Further, in the laser interferometer receiver provided by the invention, the comparator is a zero-crossing comparator, and the preset value of the comparator is 0.
Further, in the laser interferometer receiver provided by the invention, the weak signal suppression unit is a resistor voltage divider, and when the voltage signal output by the AGC unit is smaller than (Va + Vb)/2, the output of the comparator is turned off; when the voltage signal output by the AGC unit is greater than (Va + Vb)/2, the output of the comparator is switched on; wherein (Va + Vb)/2 is a reference voltage of the weak signal suppression unit, Va is a voltage value output by the AGC unit when no signal is input, and Vb is a voltage value output by the AGC unit when the weakest signal is input.
Compared with the prior art, the invention decomposes the receivable total frequency bandwidth of the band-pass filtering unit in the traditional receiver into a plurality of channel band-pass filtering units with different sub-frequency bandwidths, selects the channel band-pass filtering unit falling into the corresponding sub-frequency bandwidth to carry out band-pass filtering according to the frequency of the input signal, namely carries out band-pass filtering in the narrower sub-frequency bandwidth, overcomes the frequency noise interference of the traditional receiver in the wider frequency range in the receivable total frequency bandwidth, has good filtering effect, reduces or removes the noise in the frequency bandwidths except the corresponding channel band-pass filtering units, not only improves the measuring precision and the measuring efficiency, but also increases the channel number of the measuring optical path by decomposing the receivable frequency bandwidth into a plurality of channel bandwidth filtering units with a plurality of sub-frequency bandwidths. Through the design of the multi-channel filtering unit, the ratio of the useful signal to the noise signal is obviously improved, namely the signal-to-noise ratio is improved. The invention can reduce the requirement of the receiver on the optical power of the interference optical signal by improving the signal-to-noise ratio, thereby increasing the channel number of the measuring optical path. According to the invention, the phase compensation unit is added behind the multi-channel band-pass filtering unit, so that the phase offset of the filtered signal is compensated, the measurement error caused by the phase offset is reduced, and the measurement efficiency and the measurement precision are further improved. The invention adds a control unit which sets the phase compensation parameter according to the output frequency of the comparator and controls the channel gating of the multi-channel filter unit to close the signal loop, thereby further improving the measurement efficiency and the measurement precision.
Drawings
FIG. 1 is a schematic diagram of a conventional interferometric receiver;
FIG. 2 is a block schematic diagram of a laser interferometer receiver according to an embodiment of the present invention;
FIGS. 3 to 4 are schematic block diagrams of a laser interferometer receiver according to a first embodiment of the present invention;
FIG. 5 is a block schematic diagram of a channel bandpass filter according to a first embodiment of the invention;
FIG. 6 is a block schematic diagram of a laser interferometer receiver according to a second embodiment of the present invention;
FIG. 7 is a block schematic diagram of a laser interferometer receiver in accordance with a third embodiment of the invention;
fig. 8 is a schematic circuit diagram of an adjustable bandpass filter according to a third embodiment of the invention;
fig. 9 is an equivalent circuit schematic of the adjustable bandpass filter of fig. 8.
Shown in the figure: 210. the device comprises an optical signal detection unit, 220, an I/V conversion unit, 230, a multi-channel band-pass filtering unit, 231, a switch, 232, a multi-channel band-pass filter, 2321, a first channel band-pass filter, 2322, a second channel band-pass filter, 2323, a third channel band-pass filter, 2324, a fourth channel band-pass filter, 2325, a first channel band-pass filter, 233, a summation unit, 244, an adjustable band-pass filter, 240, an AGC unit, 250, a phase compensation unit, 260, a comparator, 270, a weak signal suppression unit, 280 and a control unit.
Detailed Description
The invention is described in further detail below with reference to the figures and specific examples. Advantages and features of the present invention will become apparent from the following description and from the claims.
Example one
Referring to fig. 2 to 5, a laser interferometer receiver according to an embodiment of the present invention includes a photo-detection unit 210, an I/V conversion unit 220, a multi-channel band-pass filtering unit 230, an AGC unit 240, a phase compensation unit 250, a comparator 260, a weak signal suppression unit 270, and a control unit 280.
The photo-detection unit 210 is configured to detect an interference light signal emitted by the laser interferometer and convert the interference light signal into an analog current signal. The photo detection unit 210 may be a photodiode.
Referring to fig. 2 to 4, the I/V conversion unit 220 is used for converting the analog current signal converted by the photo detection unit 210 into an analog voltage signal.
Referring to fig. 2 to 4, the multi-channel band-pass filtering unit 230 is configured to select a channel with a sub-frequency bandwidth in a narrow frequency range within a receivable frequency bandwidth of 0.1 to 10MHz, so as to perform band-pass filtering on the voltage signal output by the I/V conversion unit 220, so as to pass through the analog voltage signal satisfying the sub-frequency bandwidth of the channel, and remove the noise signal. The receivable frequency bandwidth is a wide band, and the sub-frequency bandwidth is a narrow band.
Referring to fig. 3 and 4, the multi-channel band-pass filtering unit 230 includes a switch 231 and a plurality of multi-channel band-pass filters 232 with different frequency bandwidths. The switch 231 may be a high-speed analog switch for turning on one channel of the multi-channel band-pass filter 232 and turning off the rest of the channels. The multi-channel band-pass filter 232 in the embodiment of the present invention includes, but is not limited to, 5, which in turn is:
a first channel band-pass filter 2321, the sub-frequency bandwidth of which is 0.1-2MHz, and the center frequency of which is 1 MHz;
a second channel band-pass filter 2322, the sub-frequency bandwidth of which is 2-4MHz, and the center frequency of which is 3 MHz;
a third channel band-pass filter 2323, the sub-frequency bandwidth of which is 4-6MHz and the central frequency of which is 5 MHz;
a fourth channel band-pass filter 2324, the sub-frequency bandwidth of which is 6-8MHz, and the central frequency of which is 7 MHz;
and a fifth channel band-pass filter 2325, the sub-frequency bandwidth of which is 8-10MHz, and the center frequency of which is 9 MHz.
Referring to fig. 5, the first to fifth channel bandpass filters may adopt an LC bandpass filter formed by an inductor L and a capacitor C connected in parallel, and the values of the inductor L and the capacitor C are adjusted to adjust the frequency bandwidth of each channel bandpass filter. At this time, the switch 231 may be a 5-bit high-speed analog switch, and when the switch 231 is turned on, only one of the first to fifth channel bandpass filters is turned on, and the rest are turned off. I.e. a channel band-pass filter that gates the input frequency signal to fall within a sub-frequency bandwidth according to the input frequency signal.
Referring to fig. 2 to 5, the AGC unit 240 is configured to amplify the analog voltage signal band-pass filtered by the multi-channel band-pass filtering unit 230.
Referring to fig. 2 to 5, the phase compensation unit 250 is configured to compensate for a phase offset caused by the voltage signal band-pass filtered by the multi-channel band-pass filtering unit 230. The phase compensation unit 250 may be a digital potentiometer, and compensates for a phase offset generated by the band-pass filtered voltage signal through a resistance change of the digital potentiometer.
Referring to fig. 2 to 5, the comparator 260 is used for comparing the analog voltage signal compensated by the phase compensation unit 250 with a predetermined value. When the analog voltage signal compensated by the phase compensation unit is greater than the preset value, the comparator 260 outputs a high level, and when the analog voltage signal compensated by the phase compensation unit is less than the preset value, the comparator 260 outputs a low level, so that the analog voltage signal output by the comparator 260 is converted into a digital voltage signal, i.e., a digital voltage signal having the same frequency as the photodetection unit 210, which is a square wave. That is, the comparator 260 converts the analog signal of the previous stage into a digital signal. The comparator 260 may be a zero-crossing comparator, and the preset value of the zero-crossing comparator is 0.
Referring to fig. 2 to 5, the weak signal suppressing unit 270 is configured to determine whether to turn off the output of the comparator 260 according to the amplitude of the analog voltage signal amplified by the AGC unit 240. The weak signal suppressing unit 270 may employ a resistor voltage divider. For example, the judgment amplitude is determined by adjusting the resistor divider in the range of 0-1000mV, and the voltage values Va and Vb outputted by the AGC unit 240 when no signal and the weakest required signal are inputted are respectively measured, wherein Vb > Va, and the voltage divider is adjusted to make the output voltage equal to (Va + Vb)/2. That is, (Va + Vb)/2 is a reference voltage of the weak signal suppression unit 270, and when the voltage signal output from the AGC unit 240 is smaller than (Va + Vb)/2, the output of the comparator 260 is turned off, and when the voltage signal output from the AGC unit 240 is larger than (Va + Vb)/2, the output of the comparator 260 is turned on.
Referring to fig. 2 to 5, the control unit 280 scans and locks the frequency of the input interference optical signal according to the current frequency value output by the comparator 260, and positions and gates the channel bandpass filtering unit of a certain sub-frequency bandwidth in the multi-channel bandpass filtering unit 230 to perform bandpass filtering, that is, gates the frequency of the interference optical signal in the certain channel bandpass filtering unit of the sub-frequency bandwidth to perform bandpass filtering. And setting a phase parameter of the phase compensation unit 250 according to the current frequency value output by the comparator 260, so as to compensate for the phase offset caused by the analog voltage signal filtered by the multi-channel band-pass filtering unit 230. Wherein the control unit 280 may employ a Complex Programmable Logic Device (CPLD).
Referring to fig. 4, the first embodiment of the present invention has the following working principle:
the photo-detection unit 210 converts the interference optical signal with a certain frequency picked up and detected by the laser interferometer into an analog current signal, converts the analog current signal into an analog voltage signal through the I/V conversion unit 220, the analog voltage signal with a certain frequency is amplified through the AGC unit 240 after being filtered by one of the multi-channel band-pass filter units 230, one path of the amplified analog voltage signal is input to the weak signal suppression unit 270, the other path of the amplified analog voltage signal is corrected for the phase through the phase compensation unit 250 and then is input to the comparator 260, the comparator 260 compares the input analog voltage signal with the preset value of the comparator 260, when the analog voltage signal is greater than the preset value, a digital high level signal is output, when the analog voltage signal is less than the preset value, a digital low level signal is output, thereby converting the optical signal input by the photo-detection unit 210 into a digital voltage signal, the control unit 280 switches the channels of the multi-channel band-pass filtering unit 230 according to the frequency of the digital voltage signal output by the comparator 260 until the frequency of the input optical signal is filtered in the channel satisfying the frequency bandwidth, and simultaneously the control unit 280 sets the parameters of the phase compensation unit according to the frequency of the digital voltage signal output by the comparator 260 to compensate for the phase offset generated after filtering by the multi-channel band-pass filtering unit 230. When the input signal frequency of the photodetection unit 210 is not within the receivable frequency bandwidth, i.e. the input signal frequency does not match the receivable frequency bandwidth, the weak signal suppression unit 270 receives noise with low amplitude, and the output of the comparator 260 is turned off by the weak signal suppression unit 270. When the input signal frequency of the photodetection unit 210 is within the receivable frequency bandwidth, the comparator 260 is turned on.
The principle that the control unit 280 switches the channels of the multi-channel band-pass filtering unit 230 according to the frequency of the digital voltage signal output by the comparator 260 is as follows: for example, when the frequency of the interference light signal input by the photo detection unit 210 is 5MHz, the frequency feedback signal f output by the comparator 260 is 0, the control unit 280 firstly switches on the first channel band-pass filter 2321 according to the frequency feedback signal f, at this time, since the sub-frequency bandwidth of the first band-pass filter 2321 is 0.1-2MHz, the frequency of the 5MHz signal cannot pass but is removed as noise, the AGC unit 240 outputs 0, the accompanying compensation unit 250 does not compensate the phase, the comparator 260 outputs 0, the control unit 280 secondly switches on the second channel band-pass filter 2322 according to the frequency feedback signal, at this time, since the sub-frequency bandwidth of the second band-pass filter 2322 is 2-4MHz, the output of the comparator 260 remains 0, the control unit 280 secondly switches on the third channel band-pass filter 2323 according to the frequency feedback signal, at this time, since the sub-frequency bandwidth of the third band-pass filter 2323 is 4-6MHz, the 5MHz signal frequency is within the sub-frequency bandwidth of the third band-pass filter 2323, and after being amplified by the AGC unit 240, the comparator compares the amplified analog voltage signal with the preset value of the comparator 260, so as to output a digital voltage signal, and the control unit 280 sets the compensation parameter of the phase compensation unit 250 according to the frequency of the digital voltage signal and the accompanying offset generated after filtering by the third band-pass filter, and sends the compensation parameter to the comparator 260 to output the phase-corrected digital voltage signal. That is, the first to fifth channel band pass filters of the embodiment of the present invention are switched cycle by cycle, and the start point of the switching order may be any one of the first to fifth channel band pass filters. The switching sequence may be performed in a forward order or in a reverse order.
The embodiment of the invention firstly decomposes the receivable total frequency bandwidth of the band-pass filtering unit in the traditional receiver into a plurality of channel band-pass filtering units with different sub-frequency bandwidths, selects the channel band-pass filtering unit falling into the corresponding sub-frequency bandwidth to carry out band-pass filtering according to the frequency of an input signal, namely carries out band-pass filtering in a narrower sub-frequency bandwidth, overcomes the frequency noise interference of the traditional receiver in a wider frequency range in the receivable total frequency bandwidth, has good filtering effect, reduces or removes the noise in the frequency bandwidths except the corresponding channel band-pass filtering units, not only improves the measurement precision and the measurement efficiency, but also increases the channel number of a measurement optical path by decomposing the receivable frequency bandwidth into a plurality of channel bandwidth filtering units with a plurality of sub-frequency bandwidths. Through the design of the multi-channel filtering unit, the ratio of the useful signal to the noise signal is obviously improved, namely the signal-to-noise ratio is improved. The invention can reduce the requirement of the receiver on the optical power of the interference optical signal by improving the signal-to-noise ratio, thereby increasing the channel number of the measuring optical path. According to the invention, the phase compensation unit is added behind the multi-channel band-pass filtering unit, so that the phase offset of the filtered signal is compensated, the measurement error caused by the phase offset is reduced, and the measurement efficiency and the measurement precision are further improved. The invention adds a control unit which sets the phase compensation parameter according to the output frequency of the comparator and controls the channel gating of the multi-channel filter unit to close the signal loop, thereby further improving the measurement efficiency and the measurement precision.
Example two
Referring to fig. 6, the second embodiment of the present invention is improved on the basis of the first embodiment, and the difference is that the multi-channel band-pass filtering unit 230 may further include a summing unit 233, which is used for performing summation on a gated channel band-pass filter 232 and a simultaneously closed channel band-pass filter 232, so as to ensure accuracy of a sum signal obtained by the summing unit, and avoid noise generated when the multi-channel band-pass filtering unit 230 switches channels, thereby improving measurement efficiency and measurement accuracy. That is, the summing unit 233 can smoothly perform transition switching between channels. The summing unit 233 may employ an adder.
EXAMPLE III
Referring to fig. 2 and fig. 7, a third embodiment of the present invention is improved on the basis of the first embodiment, and is different in that the multi-channel band-pass filtering unit 230 is an adjustable band-pass filter 234. For example: the overall frequency bandwidth of the adjustable band-pass filter 234 is 0.1-10MHz, and the adjustable band-pass filter 234 can be adjusted to a plurality of sub-frequency bandwidths with narrower frequency bandwidths within the frequency bandwidth of 0.1-10 MHz.
Referring to fig. 8 and 9, the adjustable bandpass filter 234 according to the third embodiment of the present invention adopts an LC resonant filter with adjustable frequency bandwidth, which is formed by connecting an inductor L1 and a varactor VD1 in parallel. In this case, the varactor VD1 is used in reverse.
The third embodiment of the present invention basically has the same operation principle as the first embodiment, and the difference is that the switching of the sub-frequency bandwidth of the band-pass filter 234 can be adjusted. The I/V conversion unit 220 adjusts the capacitance value of the equivalent capacitor C1 of the varactor VD1 by applying a reverse bias voltage to the varactor VD1, thereby making the center frequency of the frequency bandwidth adjustable LC resonator filter within a receivable frequency bandwidth. For example, when the frequency of the interference light signal input by the photodetection unit 210 is 5MHz, the I/V conversion unit 220 converts the current signal detected by the photodetection unit 210 into an analog voltage signal, and the reverse input terminal of the varactor VD1 of the adjustable band-pass filter 234 adjusts the capacitance value of the equivalent capacitor C1 of the varactor VD1 according to the amplitude of the analog voltage signal, so as to change the frequency bandwidth of the adjustable band-pass filter 234 to a certain sub-frequency bandwidth, and then the analog voltage signal is band-pass filtered through the channel corresponding to the sub-frequency bandwidth. After the phase is amplified by the AGC unit 240 and corrected by the phase compensation unit 250, the phase is sent to the comparator 260, and the control unit 280 positions the center frequency of the adjustable band pass filter 234 according to the current frequency value of the comparator 260, so as to implement frequency scanning and locking, and sets the parameters of the phase compensation unit 250 according to the current frequency value.
The control unit 280 firstly needs to scan and locate the frequency bandwidth of the adjustable band-pass filter 234, when the receivable total frequency bandwidth is not matched with the frequency of the input signal, the noise with low amplitude is received by the subsequent stage, and at this time, the output of the comparator 260 is closed by the weak signal suppression unit 270, so as to determine the currently working frequency point. Because the frequency variation of two adjacent periodic waves is small, after the frequency feedback is formed, the center frequency of the adjustable band-pass filter 234 and the corresponding phase compensation parameter can be changed in real time according to the frequency value obtained by the frequency feedback, so that the band-pass filtering unit with the receivable overall frequency bandwidth is changed into a narrower sub-frequency bandwidth filter. That is, the core idea of the present invention is to decompose the receivable overall frequency bandwidth into a sub-frequency bandwidth which becomes a factor N, thereby dividing the overall frequency bandwidth of a fixed one channel into a sub-frequency bandwidth channel of a plurality of sub-frequency bandwidths. The method and the device improve the pick-up capability of interference optical signals, obtain high signal-to-noise ratio, increase the number of channels of a measuring optical path, and improve the stability and the precision of measurement.
For example, varactor VD1 is required to have a 1:100 tuning range, which may be 1pF-100 pF. According to the central frequency calculation formula
The required inductance value can be obtained in the order of several henries. In addition, the inductor can be replaced by an active network (namely, an analog inductor or an equivalent inductor) formed by RC, and a high-speed operational amplifier design is adopted, so that the central frequency can be adjusted within the range of 0.1-10 MHz. And a multistage cascade mode can be used for realizing high-order filtering, and the center frequency of each stage is adjusted to achieve a better filtering effect.
The above description is only for the purpose of describing the preferred embodiments of the present invention, and is not intended to limit the scope of the present invention, and any variations and modifications made by those skilled in the art based on the above disclosure are within the scope of the appended claims.
Claims (12)
1. A laser interferometer receiver, comprising:
the photoelectric detection unit is used for detecting an interference light signal emitted by the laser interferometer and converting the interference light signal into an analog current signal;
an I/V conversion unit for converting the analog current signal converted by the photoelectric detection unit into an analog voltage signal;
the multi-channel band-pass filtering unit is used for selecting a certain channel of a sub-frequency bandwidth with a narrow frequency range in a receivable frequency bandwidth so as to carry out band-pass filtering on the analog voltage signal output by the I/V conversion unit;
the AGC unit is used for amplifying the analog voltage signal subjected to band-pass filtering by the multi-channel band-pass filtering unit;
the phase compensation unit is used for compensating phase deviation caused by the analog voltage signal subjected to band-pass filtering by the multi-channel band-pass filtering unit;
the comparator is used for comparing the analog voltage signal compensated by the phase compensation unit with a preset value, and when the analog voltage signal compensated by the phase compensation unit is greater than the preset value, the comparator outputs a high level; when the analog voltage signal compensated by the phase compensation unit is smaller than a preset value, the comparator outputs a low level to convert the analog voltage signal output by the comparator into a digital voltage signal;
the weak signal suppression unit is used for judging whether to close the output of the comparator according to the amplitude of the analog voltage signal amplified by the AGC unit;
and the control unit is used for positioning and gating the channel band-pass filtering unit with a certain sub-frequency bandwidth in the multi-channel band-pass filtering unit to carry out band-pass filtering according to the current frequency value output by the comparator, and setting the phase parameter of the phase compensation unit according to the current frequency value output by the comparator so as to compensate the phase offset caused by the analog voltage signal filtered by the multi-channel band-pass filtering unit.
2. The laser interferometer receiver of claim 1, wherein the multi-channel bandpass filtering unit comprises a plurality of multi-channel bandpass filters of different sub-frequency bandwidths and a switch for switching on one of the channels and switching off the remaining channels.
3. A laser interferometer receiver as claimed in claim 2, wherein the switch is a multi-bit high speed analogue switch.
4. A laser interferometer receiver as claimed in claim 2, wherein the multi-channel band pass filter comprises:
the sub-frequency bandwidth of the first channel band-pass filter is 0.1-2MHz, and the central frequency is 1 MHz;
the sub-frequency bandwidth of the second channel band-pass filter is 2-4MHz, and the central frequency is 3 MHz;
the sub-frequency bandwidth of the third channel band-pass filter is 4-6MHz, and the central frequency is 5 MHz;
the sub-frequency bandwidth of the fourth channel band-pass filter is 6-8MHz, and the central frequency of the fourth channel band-pass filter is 7 MHz;
and a fifth channel band-pass filter, wherein the sub-frequency bandwidth is 8-10MHz, and the center frequency is 9 MHz.
5. The laser interferometer receiver of claim 4, wherein any one of the multi-channel bandpass filters is an LC bandpass filter consisting of an inductor L and a capacitor C connected in parallel.
6. The laser interferometer receiver of claim 2, wherein the multi-channel bandpass filtering unit further comprises a summing unit connected after the multi-channel bandpass filter for adding and de-noising the gated one of the channel bandpass filters and the simultaneously turned off one of the channel bandpass filters.
7. A laser interferometer receiver as claimed in claim 6, wherein the summing unit is an adder.
8. A laser interferometer receiver as claimed in claim 1, wherein the multi-channel bandpass filtering unit is a tunable bandpass filter.
9. The laser interferometer receiver of claim 8, wherein the adjustable bandpass filter is an LC resonant filter with adjustable frequency bandwidth formed by an inductor L1 in parallel with a varactor VD 1.
10. The laser interferometer receiver of claim 1, wherein the phase compensation unit is a digital potentiometer, and the control unit adjusts a resistance change of the digital potentiometer based on the current frequency value output by the comparator to compensate for a phase offset generated by the band-pass filtered analog voltage signal.
11. The laser interferometer receiver of claim 1, wherein the comparator is a zero-crossing comparator, the comparator having a preset value of 0.
12. The laser interferometer receiver of claim 1, wherein the weak signal rejection unit is a resistor divider that turns off the output of the comparator when the voltage signal output by the AGC unit is less than (Va + Vb)/2; when the voltage signal output by the AGC unit is greater than (Va + Vb)/2, the output of the comparator is switched on; wherein (Va + Vb)/2 is a reference voltage of the weak signal suppression unit, Va is a voltage value output by the AGC unit when no signal is input, and Vb is a voltage value output by the AGC unit when the weakest signal is input.
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