High-bandwidth low-delay interferometer signal processing card

Abstract

The invention provides a high-bandwidth low-delay interferometer signal processing card, and the card comprises a dual-frequency signal processing unit which collects a temperature value, determines a DC component and an AC component in a voltage signal corresponding to a target optical signal emitted by a dual-frequency laser interferometer, and transmits the temperature value, the DC component and the AC component to a resolving unit; the resolving unit is used for adjusting the optical signal conversion gain in real time according to the temperature value and the direct-current component of the voltage signal, and determining the displacement of the to-be-measured equipment on a target axis corresponding to the measurement optical signal according to the alternating-current components of the voltage signal corresponding to the reference optical signal and the measurement optical signal respectively; the frequency synchronization control unit is used for sending a frequency signal to each dual-frequency signal processing unit to realize sampling frequency synchronization; and the auxiliary unit is used for converting electric energy of an external power supply into a first power supply required by the double-frequency signal processing unit and a second power supply required by the frequency synchronization control unit, and providing different grounding ends for the double-frequency signal processing unit and the frequency synchronization control unit.

Description

Technical Field

[0001] This application relates to the technical field of displacement monitoring, and particularly to a high-bandwidth and low-latency interferometer signal processing card. Background Art

[0002] In high-tech fields such as ultra-precision manufacturing, precision motion platform control, microelectronics, and biomedicine, it is necessary to measure the displacement of production equipment during the production process, and the measurement accuracy is relatively high, requiring nanoscale displacement monitoring. For example, the calibration requirements of high-precision CNC machine tools are often at the nanometer level, with a typical accuracy range of 10 to 500 nanometers, to ensure the reliability of machining accuracy. In the microelectronics industry, the chip process has gradually evolved towards the 3-nanometer node, posing higher accuracy requirements for displacement measurement during manufacturing to support the yield of chips. In addition, in biomedical research, cell morphology measurement and tissue surface observation also rely on nanoscale displacement detection to support in-depth research at the microscopic scale.

[0003] Among these high-precision measurement technologies, the heterodyne laser interferometer has become the core technology for nanoscale displacement detection due to its characteristics such as non-contact measurement, high resolution, strong anti-interference ability, and wide measurement range. The heterodyne laser interference technology is based on the improvement of the Michelson interferometer, and its core principle is to use two light beams with different frequencies as the light source. The frequency difference between the two optical signals with different frequencies is usually between several kilohertz and several tens of megahertz. By introducing the light source into the optical path of the measurement processing card to form interference and generate a beat frequency signal, the precise detection of displacement can be achieved by accurately measuring the phase difference between the reference signal and the interference signal.

[0004] In the prior art, for example, in the patent with the application number 200710099496.2, it is disclosed that a dual-frequency laser interferometer is used to provide multi-axis measurement signals and reference signals, and each signal is filtered and amplified. Under the condition that the aperture time of the high-speed analog-to-digital converter is small enough and the measurement trigger clock synchronously drives the high-speed analog-to-digital converter and the high-speed field programmable gate array FPGA, the high-speed analog-to-digital converter is used to perform analog-to-digital conversion on all signals respectively. Finally, the high-speed field programmable gate array calculates the integer part and decimal part of multiple axes and the integer part and decimal part of the reference axis to solve the displacement and output the displacement data of each axis.

[0005] However, the above method does not consider that as the number of measurement axes increases, it will lead to an increase in overall power consumption and more heat generation. This heat accumulation will not only affect the long-term stability of the device, but also introduce temperature drift, which has a negative impact on high-precision measurement results. In addition, the solution relies on a synchronous trigger clock to drive the analog-to-digital converter and the field-programmable gate array to ensure the synchronization of signals on each axis. However, as the number of axes increases, it becomes increasingly difficult to achieve high-precision clock synchronization between multiple analog-to-digital converters. Especially in nanoscale measurements, tiny synchronization errors will significantly affect the measurement accuracy of the system. Additionally, the solution inputs all the signals after analog-to-digital conversion into the field-programmable gate array for calculation. When the number of measurement axes increases, the computational burden on the field-programmable gate array rises significantly, affecting the real-time performance of the system. If the selected field-programmable gate array does not have sufficient processing power to support high-frequency data input and calculation, the response speed of the system will be limited. Moreover, it is considered that the laser interferometer providing the interference signal is ideal, without considering the deterioration of the beam quality caused by factors such as mechanical assembly errors, environmental vibrations, or the performance of optical devices, which reduces the signal-to-noise ratio of the dual-frequency signal and may be difficult to achieve the ideal measurement accuracy in practical applications. Summary of the Invention

[0006] In view of this, the purpose of this application is to provide at least a high-bandwidth and low-latency interferometer signal processing card. By setting a calculation unit, an auxiliary unit, a frequency synchronization control unit, and multiple dual-frequency signal processing units on the processing card, the voltage signals of the measurement optical signals corresponding to each moving axis and the voltage signals of the reference optical signals are determined through the multiple dual-frequency signal processing units, and the voltage signals corresponding to the measurement optical signals and the reference optical signals are respectively split into DC components and AC components. The calculation unit adjusts the optical signal conversion gain through the DC component and the temperature value where the dual-frequency signal processing unit is located, and determines the displacements on the moving axes corresponding to each measurement optical signal through the AC components corresponding to the measurement optical signals and the reference optical signals respectively. The frequency synchronization control unit synchronizes the acquisition frequencies of each dual-frequency signal processing unit according to the frequency synchronization control unit, and provides different power supplies and grounding terminals to the frequency synchronization control unit and the dual-frequency signal processing units through the set auxiliary unit, solving the technical problems of low signal-to-noise ratio of the dual-frequency signal and slow response speed caused by multiple moving axes in the prior art, and achieving the technical effects of adjusting the signal-to-noise ratio of the optical signal and improving the response speed.

[0007] This application mainly includes the following aspects:

[0008] In a first aspect, an embodiment of the present application provides a high-bandwidth and low-latency interferometer signal processing card. The processing card includes a calculation unit, an auxiliary unit, a frequency synchronization control unit, and a plurality of dual-frequency signal processing units. Among them, for each dual-frequency signal processing unit, the dual-frequency signal processing unit collects the temperature value at its location, determines the DC component and the AC component in the voltage signal corresponding to the target optical signal emitted by the dual-frequency laser interferometer, and sends the temperature value, the DC component, and the AC component to the calculation unit. The target optical signal includes the reference optical signal or the measurement optical signal received by the dual-frequency signal processing unit; the calculation unit adjusts the optical signal conversion gain in real time through the temperature value and the DC component of the voltage signal, and determines the displacement of the device under test on the target axis corresponding to the measurement optical signal through the AC components of the voltage signals corresponding to the reference optical signal and the measurement optical signal respectively. The target axis refers to one of the moving axes of the device under test when moving under multiple moving axes, and one moving axis corresponds to a dual-frequency signal processing unit that receives the measurement optical signal; the frequency synchronization control unit synchronizes the sampling frequency through the frequency signal by sending a frequency signal to each dual-frequency signal processing unit; the auxiliary unit converts the electrical energy of the external power supply into the first power supply required by the dual-frequency signal processing unit and the second power supply required by the frequency synchronization control unit, and provides different grounding terminals to the dual-frequency signal processing unit and the frequency synchronization control unit to eliminate interference.

[0009] Optionally, the processing card further includes a cascading module for connecting other processing cards. For each dual-frequency signal processing unit, the dual-frequency signal processing unit includes a conversion module. A plurality of processing cards are sequentially connected through the cascading module. The plurality of processing cards include a main processing card and at least one slave processing card. The conversion module of the first dual-frequency signal processing unit among the plurality of dual-frequency signal processing units of the main processing card receives the reference optical signal emitted by the dual-frequency laser interferometer and converts the reference optical signal into a reference voltage signal. The other dual-frequency signal processing units of the main processing card and each dual-frequency signal processing unit in at least one slave processing card serve as second dual-frequency signal processing units. The conversion module of the first dual-frequency signal processing unit receives the reference optical signal of the reference axis corresponding to the dual-frequency laser interferometer and converts the reference optical signal into the reference voltage signal, and sends it to the cascading module of the slave processing card connected thereto through the cascading module of the main processing card, so that each sequentially connected slave processing card forwards the reference voltage signal one by one. The conversion module of the second dual-frequency signal processing unit receives the measurement optical signal of the target axis corresponding to the dual-frequency laser interferometer and converts the measurement optical signal into a measurement voltage signal. Wherein, the conversion module includes a high-voltage circuit, an avalanche photodiode and a voltage conversion circuit. The avalanche photodiode is arranged between the high-voltage circuit and the voltage conversion circuit. The high-voltage circuit provides a reverse bias voltage to the avalanche photodiode. The avalanche photodiode is used to convert the collected reference optical signal or measurement optical signal emitted by the dual-frequency laser interferometer into a corresponding current signal. The voltage conversion circuit is used to convert the current signal corresponding to the reference optical signal into a reference voltage signal or convert the current signal corresponding to the measurement optical signal into a measurement voltage signal.

[0010] Optionally, the solving unit includes a solving module. For each dual-frequency signal processing unit, the dual-frequency signal processing unit further includes a separating module, a first multiplexing module, a first analog-to-digital conversion module, and a signal conversion module. The first multiplexing module includes a temperature collector, and the temperature collector is configured to collect the temperature value of the avalanche photodiode of the conversion module of the dual-frequency signal processing unit. Wherein, the separating module is connected to the conversion module and the cascading module of the dual-frequency signal processing unit, and resolves the DC component and the AC component from the voltage signals respectively output by the conversion module and the cascading module. The first multiplexing module respectively sends the temperature value and the DC component to the first analog-to-digital conversion module. The first analog-to-digital conversion module converts the temperature value into a temperature digital signal and converts the DC component into a DC digital signal, and then sequentially sends the temperature digital signal and the DC digital signal to the solving module. The solving module determines a voltage regulation digital signal for real-time adjustment of the optical signal conversion gain according to the temperature digital signal and the DC digital signal. The signal conversion module determines a voltage regulation analog signal for the high-voltage circuit of the conversion module according to the voltage regulation digital signal, so that the high-voltage circuit provides the reverse bias voltage to the avalanche photodiode according to the voltage regulation analog signal.

[0011] Optionally, for each dual-frequency signal processing unit, the dual-frequency signal processing unit further includes a second multiplexing module and a second analog-to-digital conversion module. The second multiplexing module includes a digital frequency synthesizer, and the digital frequency synthesizer is configured to simulate a measurement signal corresponding to the measurement optical signal or a reference signal corresponding to the reference optical signal. Wherein, the second multiplexing module sends the AC component output by the separating module to the second analog-to-digital conversion module. The second analog-to-digital conversion module converts the AC component into an AC digital signal, and the solving module determines the displacement on the target axis according to the AC digital signal. Alternatively, the second multiplexing module sends the measurement signal or the reference signal to the second analog-to-digital conversion module, and the second analog-to-digital conversion module respectively converts the measurement signal or the reference signal into a digital signal for self-checking. The solving module performs self-checking according to the digital signal.

[0012] Optionally, for each dual-frequency signal processing unit, the dual-frequency signal processing unit further includes a first single-ended to differential module and a second single-ended to differential module. Among them, the first single-ended to differential module is disposed between the first multiplexing module and the first analog-to-digital conversion module, and is configured to convert the temperature value into a temperature differential signal or convert the DC component into a DC differential signal, so that the first analog-to-digital conversion module converts the temperature differential signal into a temperature digital signal or converts the DC differential signal into a DC digital signal. The second single-ended to differential module is disposed between the second multiplexing module and the second analog-to-digital conversion module, and is configured to convert the measurement signal or the reference signal into an analog differential signal respectively, or convert the AC component into an AC differential signal, so that the second analog-to-digital conversion module converts the analog differential signal into a digital signal for self-check or converts the AC differential signal into an AC digital signal.

[0013] Optionally, the frequency synchronization control unit includes a reference frequency generation module, a frequency synchronization module, and a differential driver. The working modules of the frequency synchronization control units corresponding to the main processing card and each slave processing card are different. The working module of the frequency synchronization control unit of the main processing card is the reference frequency generation module, and the working module of the frequency synchronization control unit of each slave processing card is the frequency synchronization module. Among them, the frequency signal includes a reference frequency signal sent by the reference frequency generation module and a synchronization frequency signal sent by the frequency synchronization control unit. The reference frequency generation module sends the reference frequency signal to each dual-frequency signal processing unit of the main processing card through the differential driver, and the reference frequency generation module sends the reference frequency signal to the frequency synchronization control unit of each slave processing card. The frequency synchronization control unit sends the synchronization frequency signal to each dual-frequency signal processing unit of its corresponding slave processing card through the differential driver according to the reference frequency signal.

[0014] Optionally, the reference frequency generation module includes a first oscillator and a first clock distributor. Among them, the first oscillator inputs a first initial frequency signal to the first clock distributor. The first clock distributor splits the first initial frequency signal through clock distribution into a first reference frequency signal and a second reference frequency signal, sends the first reference frequency signal to the differential driver, sends the second reference frequency signal to the frequency synchronization control unit of each slave processing card, and the differential driver sends the first reference frequency signal to each dual-frequency signal processing unit of the main processing card.

[0015] Optionally, the frequency synchronization module includes a second oscillator, a second clock distributor, a phase detector, and a proportional-integral circuit. Among them, the second oscillator inputs a second initial frequency signal to the second clock distributor. The second clock distributor splits the second initial frequency signal through clock distribution into a first synchronization frequency signal and a second synchronization frequency signal, sends the first synchronization frequency signal to the differential driver, and sends the second synchronization frequency signal to the phase detector. The differential driver sends the first synchronization frequency signal to each dual-frequency signal processing unit of the slave processing card. The phase detector outputs a phase difference signal to the proportional-integral circuit by comparing the second basic frequency signal and the second synchronization frequency signal. The proportional-integral circuit determines the control voltage applied to the second oscillator through the phase difference signal, so that the second oscillator outputs the first synchronization frequency signal with the same frequency as the first basic frequency signal according to the control voltage.

[0016] Optionally, the first oscillator includes a programmable oscillator or a resolution module in the first dual-frequency signal processing unit of the processing card.

[0017] Optionally, the processing card further includes a communication interface and an indicator light. The communication interface is used to connect to the host computer. Among them, the resolution unit transmits the displacement of each dual-frequency signal processing unit corresponding to the reference optical signal on the target axis to the host computer through the communication interface, and receives the reference voltage signal or the measured voltage signal determined by each dual-frequency signal processing unit to determine whether the light intensity is in an abnormal state. If the light intensity is in an abnormal state, it is indicated by the indicator light.

[0018] A high-bandwidth and low-latency interferometer signal processing card provided by an embodiment of the present application. The processing card includes a calculation unit, an auxiliary unit, a frequency synchronization control unit, and a plurality of dual-frequency signal processing units. Among them, for each dual-frequency signal processing unit, the dual-frequency signal processing unit collects the temperature value at its location, and determines the direct current component and the alternating current component in the voltage signal corresponding to the target optical signal emitted by the dual-frequency laser interferometer, and sends the temperature value, the direct current component, and the alternating current component to the calculation unit. The target optical signal includes the reference optical signal or the measurement optical signal received by the dual-frequency signal processing unit; the calculation unit adjusts the optical signal conversion gain in real time through the temperature value and the direct current component of the voltage signal, and determines the displacement of the device under test on the target axis corresponding to the measurement optical signal through the alternating current components of the voltage signals corresponding to the reference optical signal and the measurement optical signal respectively. The target axis refers to a moving axis on which the device under test moves under multiple moving axes, and one moving axis corresponds to one dual-frequency signal processing unit that receives the measurement optical signal; the frequency synchronization control unit synchronizes the sampling frequency through the frequency signal by sending the frequency signal to each dual-frequency signal processing unit; the auxiliary unit converts the electrical energy of the external power supply into the first power supply required by the dual-frequency signal processing unit and the second power supply required by the frequency synchronization control unit, and provides different grounding terminals to the dual-frequency signal processing unit and the frequency synchronization control unit to eliminate interference. By setting the calculation unit, the auxiliary unit, the frequency synchronization control unit, and a plurality of dual-frequency signal processing units, the voltage signals of the measurement optical signals corresponding to each moving axis and the voltage signal of the reference optical signal are determined by the plurality of dual-frequency signal processing units, and the voltage signals corresponding to the measurement optical signal and the reference optical signal are respectively split into a direct current component and an alternating current component. The calculation unit adjusts the optical signal conversion gain through the direct current component and the temperature value where the dual-frequency signal processing unit is located, and determines the displacement on the moving axis corresponding to each measurement optical signal through the alternating current component, and the frequency synchronization control unit synchronizes the acquisition frequencies of each dual-frequency signal processing unit according to the set frequency synchronization control unit, and the set auxiliary unit provides different power supplies and grounding terminals to the frequency synchronization control unit and the dual-frequency signal processing unit, solving the technical problems of low signal-to-noise ratio of dual-frequency signals and slow response speed caused by multiple moving axes in the prior art, and achieving the technical effects of increasing the signal-to-noise ratio of optical signals and improving the response speed.

[0019] To make the above objects, features, and advantages of the present application more obvious and understandable, the following specifically enumerates preferred embodiments and, in conjunction with the accompanying drawings, makes the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] To more clearly illustrate the technical solutions of the embodiments of the present application, the accompanying drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present application and should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0021] Figure 1 It shows a schematic structural diagram of a high-bandwidth and low-latency interferometer signal processing card provided by an embodiment of the present application.

[0022] Figure 2 It shows a schematic measurement principle diagram of a dual-frequency laser interferometer provided by an embodiment of the present application.

[0023] Figure 3 It shows a schematic diagram of a dual-frequency signal processing unit provided by an embodiment of the present application.

[0024] Figure 4 It shows a schematic diagram of a dual quadrature lock-in amplification technique provided by an embodiment of the present application.

[0025] Figure 5 It shows a schematic structural diagram of a frequency synchronization control unit provided by an embodiment of the present application. Detailed implementation manners

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present application. It should be understood that the accompanying drawings in the present application only serve the purposes of illustration and description and are not used to limit the protection scope of the present application. Additionally, it should be understood that the schematic drawings are not drawn to actual scale. The flowcharts used in the present application show the operations implemented according to some embodiments of the present application. It should be understood that the operations in the flowchart may not be implemented in sequence, and steps without logical context relationships may be reversed or implemented simultaneously. In addition, those skilled in the art can add one or more other operations to the flowchart or remove one or more operations from the flowchart under the guidance of the content of the present application.

[0027] Furthermore, the described embodiments are only some embodiments of the present application, rather than all embodiments. The components of the embodiments of the present application described and shown in the accompanying drawings here can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application claimed, but only represents the selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative efforts fall within the protection scope of the present application.

[0028] In technologies such as ultra-precision manufacturing, precision motion platform control, microelectronics, and biomedicine that require high-precision measurements, the heterodyne laser interferometer has become the core technology for nanoscale displacement detection due to its non-contact measurement, high resolution, strong anti-interference ability, and wide measurement range. The heterodyne laser interference technology is based on the improvement of the Michelson interferometer, and its core principle is to use two light beams with different frequencies as the light source. The frequency difference between the two light signals with different frequencies is usually between several kilohertz and several tens of megahertz. The light source is introduced into the optical path of the measurement processing card to form interference and generate a beat signal. By accurately measuring the phase difference between the reference signal and the interference signal, precise displacement detection can be achieved.

[0029] The signal demodulation and data processing of the heterodyne laser interferometer are the keys to achieving high-precision measurement. The displacement information of the object to be measured is modulated on the phase difference of the beat signal, and the heterodyne interference processing card can calculate the tiny displacement through an accurate phase demodulation algorithm. In the prior art, the displacement measurement of multiple measurement axes is realized through multiple analog-to-digital converters and a high-speed field programmable gate array (FPGA). As the number of measurement axes increases, the number of analog-to-digital converters also needs to be increased, resulting in a significant increase in the computational burden of the FPGA, affecting the real-time performance of the processing card. If the selected FPGA does not have sufficient processing power to support high-frequency data input and calculation, the response speed of the processing card will be limited.

[0030] Based on this, the embodiments of the present application provide a high-bandwidth and low-latency interferometer signal processing card. By setting a calculation unit, an auxiliary unit, a frequency synchronization control unit, and multiple dual-frequency signal processing units, the voltage signals of the measurement optical signals corresponding to each motion axis and the voltage signals of the reference optical signals are determined through the multiple dual-frequency signal processing units, and the voltage signals corresponding to the measurement optical signals and the reference optical signals are respectively split into a DC component and an AC component. The calculation unit adjusts the optical signal conversion gain through the DC component and the temperature value where the dual-frequency signal processing unit is located, and determines the displacement on the motion axis corresponding to each measurement optical signal through the AC component. The frequency synchronization control unit synchronizes the acquisition frequencies of the multiple dual-frequency signal processing units according to the set frequency synchronization control unit, and the set auxiliary unit provides different power supplies and grounding terminals to the frequency synchronization control unit and the dual-frequency signal processing units, solving the technical problems of low signal-to-noise ratio of the dual-frequency signal and slow response speed caused by multiple motion axes in the prior art, and achieving the technical effects of increasing the signal-to-noise ratio of the optical signal and improving the response speed, specifically as follows:

[0031] Please refer to Figure 1 , Figure 1 which is a schematic structural diagram of a high-bandwidth and low-latency interferometer signal processing card provided by the embodiments of the present application. As shown in Figure 1As shown in the figure, the high-bandwidth and low-latency interferometer signal processing card 101 provided by the embodiment of the present application includes a solution unit 1011, an auxiliary unit 1014, a frequency synchronization control unit 1012, and a plurality of dual-frequency signal processing units 1013. For each dual-frequency signal processing unit, the dual-frequency signal processing unit collects the temperature value where it is located, and determines the DC component and the AC component in the voltage signal corresponding to the target optical signal emitted by the dual-frequency laser interferometer, and sends the temperature value, the DC component, and the AC component to the solution unit. The target optical signal includes the reference optical signal or the measurement optical signal received by the dual-frequency signal processing unit; the solution unit adjusts the optical signal conversion gain in real time through the temperature value and the DC component of the voltage signal, and determines the displacement of the device under test on the target axis corresponding to the measurement optical signal through the AC components of the voltage signals corresponding to the reference optical signal and the measurement optical signal respectively. The target axis refers to one of the moving axes of the device under test moving under multiple moving axes, and one moving axis corresponds to a dual-frequency signal processing unit that receives the measurement optical signal; the frequency synchronization control unit synchronizes the sampling frequency through the frequency signal by sending a frequency signal to each dual-frequency signal processing unit; the auxiliary unit converts the electrical energy of the external power supply into the first power supply required by the dual-frequency signal processing unit and the second power supply required by the frequency synchronization control unit, and provides different grounding terminals to the dual-frequency signal processing unit and the frequency synchronization control unit to eliminate interference.

[0032] Among them, the device under test can be a device such as a wafer processing device that needs to detect the displacements corresponding to each moving axis respectively. And, the dual-frequency laser interferometer can emit a test optical signal in the direction of each moving axis and a reference optical signal in the direction of a reference axis. Each moving axis is each axis for the device under test to move, and the reference axis is used as a reference for each moving axis rather than the moving axis of the device under test.

[0033] That is to say, a dual-frequency signal processing unit corresponds to receiving one optical signal, that is, the dual-frequency signal processing unit is responsible for receiving the reference optical signal, or is responsible for receiving a measurement optical signal corresponding to a target axis.

[0034] Exemplarily, please refer to Figure 2 , Figure 2 which is the measurement schematic diagram of the dual-frequency laser interferometer provided by the embodiment of the present application. As Figure 2 shown, the frequency-stabilized laser in the dual-frequency laser interferometer provided by the embodiment of the present application emits two linearly polarized lights with frequencies of f 1 and f 2 respectively, and the polarization directions are perpendicular to each other. After being divided into two paths by a non-polarizing beam splitter cube: a small part of the dual-frequency light interferes after passing through a polarizer, generating an inherent frequency difference of f 0= |f 1 - f 2 | of the reference optical signal; Most of the dual-frequency light beams enter the polarization beam splitting cube (PBS) and are separated into the measurement optical path (f 1 ) and the reference optical path (f 2 ) according to the polarization state. After being reflected by the target to be measured (chuck in the figure), the measurement optical path introduces a Doppler frequency shift Δf, and the frequency becomes f 1 + Δf, while the frequency of the reference optical path remains stable. After the two beams of light return, they are recombined by the PBS and interfere and beat through the polarizer to generate the measurement signal f 0 + Δf. By comparing the phase or frequency differences between the reference signal and the measurement signal and combining the wavelength parameters, the displacement of the target can be accurately calculated.

[0035] Among them, when the chuck moves, the frequency difference introduced in the measurement optical signal, which is proportional to the moving speed of the chuck C is the speed of light, v is the moving speed of the chuck, and f is the optical frequency. If L is set as the moving distance of the mirror, the measurement principle of the dual-frequency laser interferometer is expressed as:

[0036]

[0037] In formula (1), L is the moving distance of the chuck, that is, the displacement, a is the starting time of movement, b is the ending time of movement, t is the time, v is the moving speed of the chuck, and λ is the wavelength value of the laser at the measurement moment. Since integrating the frequency with respect to time gives the number of cycles N, and further,

[0038] During measurement, the light wave of the polarized light beam with frequency f 1 is set as E x1 , and the light wave of the polarized light beam with frequency f 2 is set as E x2 , then the plane wave equations of the two light beams are:

[0039]

[0040] In formulas (2) and (3), E 1 is the amplitude of the light wave of the polarized light beam with frequency f 1 , E 2 is the amplitude of the light wave of the polarized light beam with frequency f 2 , is the initial phase value of the polarized light beam with frequency f 1 , is the initial phase value of the polarized light beam with frequency f 2 . Since the two light waves are superimposed, the synthesized amplitude is E = E x1 + E x2, and the number of change cycles of the synthesized optical intensity is the number of cycles N. Therefore, the synthesized optical intensity I is:

[0041]

[0042] In formula (4), E 1 2 and E 2 2 correspond to the DC components (constant terms), which reflect the independent optical intensity of each beam of light. The DC components are constant and do not change with time. And 2E 1 E 2 cos{2π(f 2 -f 1 +Δf)t} corresponds to the AC component, and the frequency of this component is related to the frequency difference between the reference optical signal and the measurement optical signal. It can be seen from formula (1) that by accurately demodulating the value of Δf, the displacement information of the chuck can be extracted.

[0043] Furthermore, the dual-frequency laser interferometer can provide a measurement optical signal and a reference optical signal under each moving axis. Thus, by combining the measurement optical signal and the reference optical signal under each moving axis, the displacement under each moving axis can be determined.

[0044] Return Figure 1 , the auxiliary unit first boosts the voltage of the external power supply through the boost module, and then reduces the boosted voltage to the conversion voltage (+12V and -12V) through a DC-DC converter and provides the first ground terminal GND1. Then, it reduces the conversion voltage to the voltage required by the first power supply (+5V and -5V) through a low-dropout linear regulator LDO to provide the first power supply and the first ground terminal for the dual-frequency signal processing unit. Furthermore, each dual-frequency signal processing unit on the processing card provides the first power supply and the first ground terminal through the auxiliary unit.

[0045] Such as Figure 1As shown, the auxiliary unit first boosts the voltage of the external power supply through a boost module, and then reduces the boosted voltage to the voltage required by the second power supply (+3.3V) through a DC-DC converter and provides a second ground terminal GND2, so that the frequency synchronization control unit is connected to the second voltage and the second ground terminal GND2. Thus, the dual-frequency signal processing unit and the frequency synchronization control unit on the processing card are respectively connected to different power supplies and different ground terminals. Since the dual-frequency signal processing unit processes analog signals and the frequency synchronization control unit transmits digital signals, the electromagnetic interference generated by the rapid switching of digital signals and the level fluctuations of the ground terminal will affect the precise demodulation and calculation accuracy of analog signals. Therefore, it is necessary for the auxiliary unit to use the external power supply to provide independent power supplies and ground terminals to the dual-frequency signal processing unit and the frequency synchronization control unit respectively, and to achieve ground isolation by connecting to different ground terminals respectively, so as to improve the purity of the analog signal power supply.

[0046] Among them, by way of example, please refer to Figure 3 , Figure 3 which is a schematic diagram of the dual-frequency signal processing unit provided by the embodiment of the present application. As Figure 3 shown, the processing card further includes a cascading module 1015, and the cascading module is used to connect other processing cards. For each dual-frequency signal processing unit, the dual-frequency signal processing unit includes a conversion module 10131. Among them, multiple processing cards are sequentially connected through the cascading module. The multiple processing cards include a main processing card and at least one slave processing card. The conversion module of the first dual-frequency signal processing unit among the multiple dual-frequency signal processing units of the main processing card receives the reference optical signal emitted by the dual-frequency laser interferometer and converts the reference optical signal into a reference voltage signal. The other dual-frequency signal processing units of the main processing card and each dual-frequency signal processing unit in at least one slave processing card are used as the second dual-frequency signal processing unit. The conversion module of the first dual-frequency signal processing unit receives the reference optical signal of the reference axis corresponding to the dual-frequency laser interferometer and converts the reference optical signal into the reference voltage signal, and sends it to the cascading module of the slave processing card connected thereto through the cascading module of the main processing card, so that each sequentially connected slave processing card forwards the reference voltage signal one by one. The conversion module of the second dual-frequency signal processing unit receives the measurement optical signal of the target axis corresponding to the dual-frequency laser interferometer and converts the measurement optical signal into a measurement voltage signal.

[0047] Furthermore, the optical signals emitted by the dual-frequency laser interferometer under each moving axis and reference axis are received by multiple processing cards. A dual-frequency signal processing unit of a processing card correspondingly receives the optical signal of one axis, and this axis can be either a reference axis or a moving axis. A dual-frequency signal processing unit of a processing card among the multiple processing cards serves as the first dual-frequency signal processing unit. If the first dual-frequency signal processing unit receives the reference optical signal emitted by the dual-frequency laser interferometer, then this processing card is the main processing card. The processing cards other than the main processing card among the multiple processing cards are slave processing cards. The dual-frequency signal processing units other than the first dual-frequency signal processing unit in the main processing card and each dual-frequency signal processing unit of each slave processing card all serve as second dual-frequency signal processing units. A second dual-frequency signal processing unit correspondingly receives the measurement optical signal corresponding to one moving axis.

[0048] Furthermore, the displacements of multiple moving axes can be processed by setting multiple processing cards.

[0049] Among them, for each moving axis, the measurement optical signal corresponding to this moving axis needs to be combined with the reference optical signal to determine the displacement under this moving axis. Furthermore, each processing card needs to know the reference voltage signal corresponding to the reference optical signal. Therefore, the slave processing cards need to rely on the cascading module to obtain the reference voltage signal corresponding to the reference optical signal processed by the first dual-frequency signal processing unit of the main processing card, and the multiple processing cards are connected in sequence through the cascading module.

[0050] Exemplarily, the main processing card serves as the first processing card, and the slave processing cards are connected in sequence. That is, the input of the cascading module of the first slave processing card is connected to the output of the cascading module of the main processing card, and the output of the cascading module of the first slave processing card is connected to the input of the cascading module of the second slave processing card, and so on to achieve the sequential connection of multiple processing cards through the cascading module. Thus, the cascading module of the main processing card replicates the reference voltage signal processed by its conversion module and sends the replicated reference voltage signal to the cascading module of the first slave processing card. The cascading module of the first slave processing card replicates the received reference voltage signal and then sends it to the cascading module of the second slave processing card, that is, the current slave processing card replicates the reference voltage signal and sends it to the cascading module of the next slave processing card. Moreover, each processing card is equivalent to obtaining the reference optical signal, and the reference voltage signal after the conversion of the reference optical signal is sent down through the cascading module, rather than selectively forwarding the digital signal processed by the dual-frequency signal processing unit, which can achieve the technical effect of reducing the processing delay.

[0051] Among them, as Figure 3As shown, the conversion module 10131 includes a high-voltage circuit, an avalanche photodiode APD, and a voltage conversion circuit. The avalanche photodiode is disposed between the high-voltage circuit and the voltage conversion circuit. The high-voltage circuit provides a reverse bias voltage to the avalanche photodiode. The avalanche photodiode is configured to convert the collected reference optical signal or measurement optical signal emitted by the dual-frequency laser interferometer into a corresponding current signal. The voltage conversion circuit is configured to convert the current signal corresponding to the reference optical signal into a reference voltage signal or convert the current signal corresponding to the measurement optical signal into a measurement voltage signal.

[0052] That is to say, in the first dual-frequency signal processing unit, the avalanche photodiode of the first dual-frequency signal processing unit converts the reference optical signal into a reference current signal, and the voltage conversion circuit converts the reference current signal into a reference voltage signal, and then sends the reference voltage signal to the cascade module of the main processing card; in the second dual-frequency signal processing unit, the avalanche photodiode of the second dual-frequency signal processing unit converts the measurement optical signal in the corresponding moving axis direction into a measurement current signal, and the voltage conversion circuit converts the measurement current signal into a measurement voltage signal. The cascade module of the slave processing card is responsible for receiving the reference voltage signal provided by the adjacent processing card, and the adjacent processing card includes the main processing card or the previous slave processing card.

[0053] Among them, due to the characteristics of the multi-axis measurement processing card and the complex optical path structure, after the relatively high-power laser generated by the dual-frequency laser interferometer is transmitted and distributed by the internal optical devices, the light intensity gradually attenuates, resulting in a weak output optical signal that is vulnerable to noise. To meet the signal detection requirements under low optical power conditions, a high-gain and high-sensitivity avalanche photodiode is used as the conversion element. The APD converts the optical signal into a current signal and transmits it to the voltage conversion circuit. The voltage conversion circuit can be a transimpedance amplifier circuit, which is composed of a capacitor CF, a resistor RF, and an operational amplifier A connected in parallel. The operational amplifier is used to amplify the signal for subsequent signal processing and demodulation. The operational amplifier uses a transimpedance amplifier with high bandwidth, high gain, and low input current voltage noise to ensure the signal demodulation accuracy under high-frequency differences. The actual structure of the voltage conversion circuit is not limited, as long as the voltage conversion circuit can convert the current signal output by the avalanche photodiode into a voltage signal.

[0054] Such as Figure 3As shown, the solving unit includes a solving module ZYNQ. For each dual-frequency signal processing unit, the dual-frequency signal processing unit further includes a separation module 10132, a multiplexing module 10133, a single-ended to differential module 10134, an analog-to-digital conversion module 10135, and a signal conversion module 10136. The multiplexing module includes a first multiplexing module and a second multiplexing module. The single-ended to differential module includes a first single-ended to differential module and a second single-ended to differential module. The analog-to-digital conversion module includes a first analog-to-digital conversion module ADC1 and a second analog-to-digital conversion module ADC2. Among them, the input end of the separation module is respectively connected to the output end of the conversion module of the dual-frequency signal processing unit and the output end of the cascading module of the processing card where it is located, so as to receive the reference voltage signal or the measurement voltage signal output by the conversion module, or receive the reference voltage signal output by the cascading module.

[0055] That is to say, the cascading module of each processing card is connected to the separation module of each dual-frequency signal processing unit. The separation module of the first dual-frequency signal processing unit processes the reference voltage signal output by its conversion module, and the separation module of the first dual-frequency signal processing unit may not process the reference voltage signal copied by its conversion module. The measurement voltage signal output by the conversion module of the second dual-frequency signal processing unit is sent to its separation module, and the separation module of the second dual-frequency signal processing unit is also connected to the output end of the cascading module of the processing card where its processing unit is located to receive the reference voltage signal transmitted by the cascading module. Furthermore, the separation module of the second dual-frequency signal processing unit needs to process the measurement voltage signal it receives itself and the reference voltage signal sent by the cascading module. The separation module of the second dual-frequency signal processing unit separates and processes one voltage signal each time. The separation module of the second dual-frequency signal processing unit of the main processing card receives the measurement voltage signal output by the conversion module of the second dual-frequency signal processing unit and the reference voltage signal sent by the cascading module of the main processing card. The separation module of the second dual-frequency signal processing unit of the slave processing card receives the measurement voltage signal output by the conversion module of the second dual-frequency signal processing unit and the reference voltage signal sent by the cascading module of the slave processing card.

[0056] Among them, the output end of the separation module includes a DC output end and an AC output end. The DC output end of the separation module, the first multiplexing module, the first single-ended to differential module, and the first analog-to-digital conversion module are connected in sequence. The first multiplexing module is connected to the signal conversion module. The output end of the first analog-to-digital conversion module is connected to the solving module. The AC output end of the separation module, the second multiplexing module, the second single-ended to differential module, and the second analog-to-digital conversion module are connected in sequence. The output end of the second analog-to-digital conversion module is connected to the solving module.

[0057] Among them, the separation module resolves the DC component and the AC component from the voltage signals respectively output by the conversion module and the cascade module. The separation module of the first dual-frequency signal processing unit resolves the corresponding DC component and AC component from the reference voltage signal. The calculation module of the first dual-frequency signal processing unit calculates the reverse bias voltage applied to the avalanche photodiode according to the DC component and the temperature value of the APD corresponding to the first dual-frequency signal processing unit. Since the first dual-frequency signal processing unit corresponds to the reference light, the AC component resolved by it is not used for calculating displacement. However, since the structures of all dual-frequency signal processing units are the same, the first dual-frequency signal processing unit will also perform subsequent processing on the AC component. It's just that the calculation module will not calculate displacement when there is only the digital signal corresponding to the AC component of the reference voltage signal, and there is no need to calculate the displacement of the reference axis. The separation module of the second dual-frequency signal processing unit resolves the corresponding measured DC component and measured AC component from the measured voltage signal output by the conversion module connected to it. The separation module of the second dual-frequency signal processing unit also resolves the corresponding reference DC component and reference AC component from the reference voltage signal output by the cascade module. Furthermore, the first multiplexing module and the first analog-to-digital conversion module of the second dual-frequency signal processing unit process the measured DC component in sequence and send the processing result to the calculation module to obtain the corresponding gain. The second multiplexing module and the second analog-to-digital conversion module of the second dual-frequency signal processing unit process the measured AC component and the reference AC component in sequence and send the processing result to the calculation module, so that the calculation module of the processing card where the second dual-frequency signal processing unit is located calculates the displacement of the target axis corresponding to the second dual-frequency signal processing unit.

[0058] Exemplarily, the separation module splits out the AC component from the voltage signal output by the conversion module of the dual-frequency signal processing unit by setting a subtraction circuit, and splits out the DC component from the voltage signal by a first-order active low-pass filter circuit, thereby separating the DC component and the AC component in the voltage signal.

[0059] Among them, the first multiplexing module includes a temperature collector, which is used to collect the temperature value of the avalanche photodiode (APD) of the conversion module of this dual-frequency signal processing unit. In a preferred embodiment, the temperature collector can also be connected to a signal conversion module. When the temperature changes, it can feedback the current changed temperature to the signal conversion module. The signal conversion module can apply a voltage value to the high-voltage circuit according to the voltage adjustment analog signal and the current changed temperature, and this voltage value can be used to finely adjust the voltage output by the high-voltage circuit to increase the real-time performance and voltage accuracy.

[0060] Among them, the separation module resolves the DC component and the AC component from the voltage signal output by the conversion module of the dual-frequency signal processing unit. The first multiplexing module sends the temperature value or the DC component to the first analog-to-digital conversion module. The first analog-to-digital conversion module converts the temperature value into a temperature digital signal or converts the DC component into a DC digital signal, and then sends the temperature digital signal and the DC digital signal to the calculation module one by one. The calculation module determines a voltage adjustment digital signal for real-time adjustment of the optical signal conversion gain based on the temperature digital signal and the DC digital signal. The signal conversion module determines a voltage adjustment analog signal for the high-voltage circuit of the conversion module based on the voltage adjustment digital signal, so that the high-voltage circuit provides the reverse bias voltage to the avalanche photodiode according to the voltage adjustment analog signal.

[0061] That is to say, the signal conversion module converts the voltage adjustment digital signal provided by the calculation module into a corresponding voltage adjustment analog signal. The voltage adjustment analog signal is used to indicate the specific voltage value that the high-voltage circuit should provide to the avalanche photodiode, so that the high-voltage circuit outputs the reverse bias voltage according to this analog signal, realizing the provision of the voltage value with adjusted gain to the avalanche photodiode.

[0062] Exemplarily, the dual-frequency signal processing unit can set a separate analog-to-digital conversion module for the temperature value and the DC component. The AC component corresponding to each dual-frequency signal processing unit on a processing card requires its own dual-frequency signal processing unit to set up an analog-to-digital conversion module for processing. Or, on a processing card, a separate analog-to-digital conversion module can be used to process the temperature values and DC components corresponding to all dual-frequency signal processing units, so as to achieve the technical effect of reducing costs.

[0063] Among them, the DC component reflects the off-axis degree and coincidence degree of the spot of the reference optical signal and the measurement optical signal output by the dual-frequency laser interferometer. The avalanche photodiode is sensitive to temperature changes. Therefore, it is necessary to consider both the off-axis degree and coincidence degree of the spot, which affects the intensity of the beat frequency light (affected by the AC component because the displacement is modulated on the AC component). The smaller the light intensity, the more easily it is affected by noise. And in actual measurement, due to multiple reflections, refractions, or angle problems of the optical signal, the optical signal reaching the dual-frequency signal processing unit will be very weak, thus making it difficult to identify the displacement. Therefore, an avalanche photodiode can be set to detect weak optical signals, and a suitable reverse bias voltage can be applied to the APD based on the temperature value where the APD is located to maintain gain stability. It can receive relatively weak optical signals and can sense light with an intensity as low as 0.07 uW (microwatt).

[0064] Therefore, the solution module monitors the temperature value where the APD is located, as well as the off-axis degree and coincidence degree between the reference beam and the measurement beam, and adjusts the reverse bias voltage applied to the APD in real time to adapt to the interference optical signals in different situations, ensuring that the APD always provides a stable and reliable current signal under temperature fluctuations, laying a foundation for the precise demodulation and processing of Δf.

[0065] Wherein, the first single-ended to differential module is arranged between the first multiplexing module and the first analog-to-digital conversion module, and is used to convert the temperature value into a temperature differential signal or convert the DC component into a DC differential signal, so that the first analog-to-digital conversion module converts the temperature differential signal into a temperature digital signal or converts the DC differential signal into a DC digital signal.

[0066] Specifically, since the anti-interference ability of the single-ended signal corresponding to the temperature value or the single-ended signal corresponding to the DC component is relatively weak, especially when processing high-frequency signals, it is easy to introduce noise and reduce the signal-to-noise ratio, thus affecting the quality of the effective signal. In addition, the single-ended signal uses the ground as the reference point. During the signal transmission process, it is difficult to keep the ground potential at different positions consistent, and it is easy to be interfered. In contrast, the converted differential signal has stronger anti-interference ability and higher stability. When external noise occurs, the interference will be almost simultaneously coupled to the two differential signal lines, and the subsequent analog-to-digital conversion module ADC only processes the difference between the two differential signals, so the common-mode noise can be effectively cancelled. In addition, the switching point of the differential signal is located at the intersection of the two signals, rather than relying on the threshold judgment of high and low levels, reducing the timing error. Through the design of the single-ended to differential module, the processing card can ensure that the signal has higher anti-interference and stability before entering the high-speed ADC, thus improving the overall measurement accuracy.

[0067] Specifically, for each dual-frequency signal processing unit, the dual-frequency signal processing unit further includes a second multiplexing module and a second analog-to-digital conversion module. The second multiplexing module includes a digital frequency synthesizer, and the digital frequency synthesizer is used to simulate a measurement signal corresponding to the measurement optical signal or a reference signal corresponding to the reference optical signal, where the simulated part is the AC component; wherein, the second multiplexing module sends the AC component output by the separation module to the second analog-to-digital conversion module, and the second analog-to-digital conversion module converts the AC component into an AC digital signal, and the solution module determines the displacement on the target axis according to the AC digital signal; or, the second multiplexing module sends the measurement signal or the reference signal to the second analog-to-digital conversion module, and the second analog-to-digital conversion module converts the measurement signal or the reference signal into digital signals for self-checking respectively, and the solution module performs self-checking according to the digital signals.

[0068] Among them, the AC component carries displacement information for subsequent signal processing to resolve the displacement information. The second multiplexing module switches between the AC component in the actual situation and the signals generated by the digital frequency synthesizer DDS for simulation. The signals generated by the digital frequency synthesizer for simulation include a reference signal for simulating the reference optical signal and a measurement signal for simulating the measurement optical signal. Thus, during the processing card debugging stage, the processing card can be monitored through the signals generated by the DDS for simulation, so as to ensure a comprehensive test and diagnosis of the processing card without relying on actual optics. Furthermore, the second analog-to-digital conversion module performs analog-to-digital conversion based on the measurement signal corresponding to the AC component of the measurement optical signal output by the second multiplexing module, or performs analog-to-digital conversion on the reference signal corresponding to the AC component of the reference optical signal for simulation, and obtains the digital signals for self-checking corresponding to the reference signal and the measurement signal respectively, so that the resolution module performs parsing according to the digital signals corresponding to the reference signal and the measurement signal respectively to perform self-detection of the processing card. The second analog-to-digital conversion module also performs analog-to-digital conversion based on the AC components corresponding to the reference optical signal or the measurement optical signal in the actual situation output by the second multiplexing module, so as to output the AC digital signals corresponding to the reference optical signal or the measurement optical signal respectively, so that the resolution module parses the AC digital signals corresponding to the reference optical signal and the measurement optical signal respectively to determine the displacement on the target axis covered by the AC component.

[0069] That is to say, when self-checking of the processing card is required, the input of the second multiplexing module is switched to the digital frequency synthesizer, so that the output of the second multiplexing module is the reference signal corresponding to the reference optical signal simulated by the digital frequency synthesizer, or the measurement signal corresponding to the measurement optical signal. Thus, self-checking of the processing card is realized by processing the reference signal and the measurement signal. At this time, there is no need for the outside world to provide actual reference optical signals or measurement optical signals. During the actual displacement determination process, the input of the second multiplexing module is the AC component corresponding to the reference voltage signal output by the separation module or the AC component corresponding to the measurement optical signal. At this time, the output of the second multiplexing module is the AC component. Thus, the resolution module parses the AC digital signal corresponding to the AC component of the reference optical signal and the AC digital signal corresponding to the AC component of the measurement optical signal to determine the displacement on the target axis covered by the AC component.

[0070] Among them, the second multiplexing module of the first dual-frequency signal processing unit receives the AC component of the reference voltage signal output by the separation module. The second multiplexing module of the second dual-frequency signal processing unit receives the reference AC component of the reference voltage signal output by the separation module, performs analog-to-digital conversion through the second analog-to-digital conversion module, and then sends it to the calculation module, so that the calculation module receives the AC digital signal corresponding to the reference AC component. The second multiplexing module also receives the measured AC component of the measured voltage signal output by the separation module, performs analog-to-digital conversion through the second analog-to-digital conversion module, and then sends it to the calculation module, so that the calculation module receives the AC digital signal corresponding to the measured AC component. Furthermore, the calculation module knows the AC digital signal corresponding to the reference AC component and the AC digital signal of the measured AC component corresponding to a target axis, and thus calculates the displacement of the target axis through phase calculation. Among them, the second multiplexing module processes one AC component each time.

[0071] Specifically, for each dual-frequency signal processing unit, the second single-ended to differential module of the dual-frequency signal processing unit is arranged between the second multiplexing module and the second analog-to-digital conversion module, and is used to convert the measurement signal or the reference signal into an analog differential signal respectively, or to convert the AC component into an AC differential signal, so that the second analog-to-digital conversion module converts the analog differential signal into a digital signal for self-testing or converts the AC differential signal into an AC digital signal.

[0072] That is to say, when the second multiplexing module outputs the measurement signal or the reference signal for self-testing, the second single-ended to differential module converts the measurement signal and the reference signal into analog differential signals respectively, and then sends the analog differential signals corresponding to the measurement signal and the reference signal to the second analog-to-digital conversion module for analog-to-digital conversion. When the second multiplexing module outputs the AC components corresponding to the measured optical signal or the reference optical signal in the actual situation, the second single-ended to differential module converts the AC component measurement signal corresponding to the measured optical signal into an AC differential signal, converts the AC component corresponding to the reference optical signal into an AC differential signal, and then sends the AC differential signals corresponding to the measured optical signal and the reference optical signal to the second analog-to-digital conversion module for analog-to-digital conversion.

[0073] Exemplarily, the solving module may select a ZYNQ chip (scalable processing platform chip), which integrates an ARM processor and an FPGA (field programmable gate array), and has the efficiency of processing complex algorithms and the flexibility of parallel computing. The FPGA part performs timing control, ADC control, data filtering, and after compensation, sends the data to the ARM to execute the phase subdivision algorithm to demodulate the displacement. The ARM processor is responsible for high-level control, data processing, and communication with the host computer, significantly reducing data latency, and increasing the reliability in high-speed and real-time displacement measurement and solving through the high performance, flexibility, and low power consumption of ZYNQ.

[0074] Exemplarily, the phase subdivision algorithm adopts the dual orthogonal lock-in amplification technique. Please refer to Figure 4 , Figure 4 which is a schematic diagram of the dual orthogonal lock-in amplification technique provided by the embodiment of the present application. As Figure 4 shown, two sine mixing signals f h and f h1 with a phase difference of 90° and a frequency of ω h2 are generated by the ARM. The AC digital signal output by the analog-to-digital conversion module is filtered and compensated by the FPGA, and the filtered and compensated data is mixed with the sine mixing signals f h1 and f h2 . The low-frequency components of the orthogonal signals obtained are acquired through the low-pass filter in the ARM:

[0075]

[0076] In formula (5), f ref is the reference optical signal, f mea is the measurement optical signal, E ref is the amplitude of the reference optical signal, E mea is the amplitude of the measurement optical signal, ω ref is the frequency of the reference optical signal, ω mea is the frequency of the measurement optical signal, is the phase of the reference optical signal, is the phase of the measurement optical signal, and sinM, cosM, sinN, and cosN are the low-frequency components of the orthogonal signals obtained after mixing. And the ARM obtains two sine and cosine signals containing the phase difference information of the reference optical signal and the measurement optical signal by operating on the low-frequency components of the orthogonal signals:

[0077]

[0078] Furthermore, the ARM calculates the data obtained in formula (6) according to the arctangent algorithm to obtain the phase difference Substituting Δf into formula (1) can calculate the displacement under the moving axis.

[0079] Please refer to Figure 5 , Figure 5 which is a schematic structural diagram of the frequency synchronization control unit provided by the embodiment of the present application. As Figure 5 shown, the frequency synchronization control unit includes a reference frequency generation module 10121, a frequency synchronization module 10122, and a differential driver 10123. The working modules of the frequency synchronization control units corresponding to the main processing card and each slave processing card are different. The working module of the frequency synchronization control unit of the main processing card is the reference frequency generation module, and the working modules of the frequency synchronization control units of each slave processing card are frequency synchronization modules. Among them, the frequency signal includes a reference frequency signal sent by the reference frequency generation module and a synchronization frequency signal sent by the frequency synchronization control unit. The reference frequency generation module sends the reference frequency signal to each dual-frequency signal processing unit of the main processing card through the differential driver, and the reference frequency generation module sends the reference frequency signal to the frequency synchronization control units of each slave processing card. The frequency synchronization control unit sends the synchronization frequency signal to each dual-frequency signal processing unit of its affiliated slave processing card through the differential driver according to the reference frequency signal.

[0080] That is to say, the frequency synchronization control unit of the main processing card sends the reference frequency signal to each dual-frequency signal processing unit of the main processing card through the reference frequency generation module and the differential driver, and the frequency synchronization control unit of the main processing card also sends the reference frequency signal to the frequency synchronization control units of each slave processing card. The frequency synchronization control unit of the slave processing card sends the synchronization frequency signal to each dual-frequency signal processing unit of the slave processing card through the frequency synchronization module and the differential driver according to the received reference frequency signal, so as to achieve frequency synchronization between the main processing card and each slave processing card. That is to say, the frequency synchronization control unit of the slave processing card synchronizes according to the reference frequency signal and sends the synchronized synchronization frequency signal to each dual-frequency signal processing unit of the slave processing card.

[0081] Among them, the frequency synchronization in the present application refers to the processing frequency synchronization of the analog-to-digital conversion modules of the dual-frequency signal processing units corresponding to the main processing card and the slave processing cards respectively, so as to achieve the clock synchronization of each processing card. Furthermore, the analog-to-digital conversion module of each dual-frequency signal processing unit in the processing card is connected to the differential driver of the frequency synchronization control unit of the processing card to receive the frequency signal output by the differential driver, so that the analog-to-digital conversion modules of each dual-frequency signal processing unit perform data processing according to the frequency of the frequency signal.

[0082] Exemplarily, the model of the differential driver is MC100EP14DTR2G, 1:5 differential, clock driver.

[0083] As Figure 5 As shown, the reference frequency generation module 10121 includes a first oscillator 201 and a first clock distributor 202. Among them, the first oscillator inputs a first initial frequency signal to the first clock distributor. The first clock distributor splits the first initial frequency signal through clock distribution to obtain a first reference frequency signal and a second reference frequency signal, sends the first reference frequency signal to the differential driver, and sends the second reference frequency signal to the frequency synchronization control unit of each slave processing card. The differential driver sends the first reference frequency signal to each dual-frequency signal processing unit of the master processing card.

[0084] Among them, the first oscillator includes a programmable oscillator XO or a solution module ZYNQ in the first dual-frequency signal processing unit of the master processing card. Furthermore, the first oscillator also includes a multiplexer MUX, which is used to select a programmable oscillator or a solution module in the first dual-frequency signal processing unit of the master processing card to provide the first initial frequency signal. The programmable oscillator can output any frequency from 10 to 810 MHz (megahertz), and the root mean square (RMS) of the clock jitter is as low as 0.5 picoseconds. Moreover, the first clock distributor is a low skew curvature 2 / 4 clock distributor, and the internal frequency dividers are mutually synchronized, so all the common output edges are precisely aligned. The 2-divided clock output by the first clock distributor is used as the first reference frequency signal, and the 4-divided clock is used as the second reference frequency signal. Furthermore, the reference frequency generation module of the master processing card sends the 2-divided clock output by the first clock distributor to each dual-frequency signal processing unit of the master processing card through the differential driver.

[0085] As Figure 5As shown, the frequency synchronization module 10122 includes a second oscillator 203, a second clock distributor 204, a phase detector 205, and a proportional-integral circuit 206. Among them, the second oscillator inputs a second initial frequency signal to the second clock distributor. The second clock distributor splits the second initial frequency signal through clock distribution into a first synchronization frequency signal and a second synchronization frequency signal, sends the first synchronization frequency signal to the differential driver, and sends the second synchronization frequency signal to the phase detector. The differential driver sends the first synchronization frequency signal to each dual-frequency signal processing unit of the slave processing card. The phase detector outputs a phase difference signal to the proportional-integral circuit by comparing the second basic frequency signal and the second synchronization frequency signal. The proportional-integral circuit determines the control voltage applied to the second oscillator through the phase difference signal, so that the second oscillator outputs the first synchronization frequency signal with the same frequency as the first basic frequency signal according to the control voltage.

[0086] Among them, the second oscillator selects a voltage-controlled crystal oscillator (VCXO), inputs the second initial frequency signal output by the crystal oscillator to the second clock distributor. The second clock distributor can select a low skew curvature 2 / 4 clock distributor, use its output 2-divided clock as the first synchronization frequency signal, use its output 4-divided clock as the second synchronization frequency signal, and input the first synchronization frequency signal to the differential driver. Then, the frequency synchronization module of the slave processing card sends the first synchronization frequency signal to each dual-frequency signal processing unit of the slave processing card through the differential driver. The frequency synchronization module 10122 further includes a fan-out driver 207. The second synchronization frequency signal enters the phase detector and receives the second reference frequency signal output by the reference frequency generation module of the master processing card through the fan-out driver, and is transmitted to the phase detector through a cable. Then, the phase detector calculates the phase difference by comparing the second reference frequency signal and the second synchronization frequency signal, and outputs a phase difference signal to the proportional-integral circuit. The proportional-integral circuit filters the high-frequency components of the phase difference signal, determines the control voltage through the low-frequency components. The control voltage is used as the control signal of the VCXO, so that the VCXO adjusts the output second initial frequency signal according to the control voltage, so that the second initial frequency signal approaches the first initial frequency signal, thereby realizing that the first synchronization frequency signal gradually approaches the frequency of the first reference frequency signal until the frequencies are the same. Exemplarily, after the phase difference between the second synchronization frequency signal of the signal processing device and the second reference frequency signal of the master signal processing device is equal to or less than 80 ps, the phase detector performs phase locking. In this way, the frequency synchronization control unit realizes the high-precision synchronization of the multi-channel data acquisition processing card, and each channel acquisition runs under the same clock reference, effectively eliminating the phase error caused by the time deviation, and ensuring the stability and accuracy of the multi-axis measurement results.

[0087] Return Figure 1 The processing card further includes a communication interface 202 and an indicator light 201. The communication interface is used to connect to a host computer. Wherein, the calculation unit transmits the displacement of each dual-frequency signal processing unit corresponding to the reference optical signal on the target axis to the host computer through the communication interface, and receives the reference voltage signal or the measured voltage signal determined by each dual-frequency signal processing unit to determine whether the light intensity is in an abnormal state. If the light intensity is in an abnormal state, it is prompted as such through the indicator light.

[0088] That is to say, for each signal processing device, when the signal processing device is the main signal processing device, the calculation module of the main signal processing device is connected to each dual-frequency signal processing unit under the signal processing device, so as to calculate the displacement under each motion axis corresponding to the measured optical signal through the reference optical signal or the measured optical signal respectively received by each dual-frequency signal processing unit; or, when the signal processing device is a slave signal processing device, the calculation module of the slave signal processing device is connected to each dual-frequency signal processing unit and the cascade module under the signal processing device, so as to calculate the displacement under each motion axis corresponding to the measured optical signal through the measured optical signal respectively received by each dual-frequency signal processing unit and the reference optical signal provided by the cascade module; thereby, the signal processing device is transmitted to the host computer through the communication interface, so that the host computer can clarify the displacement of the device under test under each motion axis.

[0089] Exemplarily, for each signal processing device, the calculation unit of the signal processing device respectively determines whether the voltage signal conforms to the voltage range for calculation through the reference voltage signal and the measured voltage signal, so as to determine whether the light intensity is in an abnormal state, that is, when the voltage signal does not conform to the voltage range for calculation, it is considered that the light intensity is in an abnormal state, and then the calculation unit prompts that the current light intensity is in an abnormal state by controlling the signal state such as the on / off of the indicator light, helping the user to quickly identify and handle abnormal situations, and ensuring the reliable operation of the entire processing card.

[0090] Furthermore, the processing card in the present application has high resolution. The number of measurement axes to be processed can be increased by connecting multiple processing cards in sequence through the cascade module, and by adjusting the signal-to-noise ratio of the optical signal, weak optical signals can be sensed and the sensitivity can be increased; it can also be paired with a dual-frequency laser interferometer with a 15MHz frequency difference to measure the displacement of a flat mirror workbench with a moving speed of ±2.2m / s.

[0091] Those skilled in the art can clearly understand that for the convenience and brevity of description, the specific working processes of the above-described processing card and device can refer to the corresponding processes in the foregoing method embodiments, and will not be elaborated herein. In several embodiments provided in the present application, it should be understood that the disclosed processing card, device, and method can be implemented in other ways. The device embodiments described above are merely illustrative. For example, the division of the units is only a logical function division, and there may be other division methods in actual implementation. For another example, multiple units or components can be combined or integrated into another processing card, or some features can be ignored or not executed. Another point is that the displayed or discussed coupling or direct coupling or communication connection between each other can be through some communication interfaces. The indirect coupling or communication connection of the device or unit can be in electrical, mechanical, or other forms.

[0092] The units described as separate components may or may not be physically separated. The components displayed as units may or may not be physical units, that is, they can be located in one place or distributed to multiple network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0093] In addition, in each embodiment of the present application, the functional units can be integrated into one processing unit, or each unit can exist physically alone, or two or more units can be integrated into one unit.

[0094] If the above functions are implemented in the form of software function units and sold or used as independent products, they can be stored in a non-volatile computer-readable storage medium executable by a processor. Based on such an understanding, the technical solution of the present application, in essence, or the part that contributes to the prior art or a part of the technical solution can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for causing a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in each embodiment of the present application. The foregoing storage medium includes: various media such as USB flash drives, mobile hard disks, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical discs that can store program codes.

[0095] The above is only the specific implementation manner of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed in the present application, and all should be covered by the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A high bandwidth low latency interferometer signal processing card, characterized in that: The processing card includes a solution unit, an auxiliary unit, a frequency synchronization control unit and a plurality of dual-frequency signal processing units. Wherein, for each dual-frequency signal processing unit, the dual-frequency signal processing unit collects the temperature value, and determines the DC component and AC component in the voltage signal corresponding to the target light signal emitted by the dual-frequency laser interferometer, and sends the temperature value, the DC component and the AC component to the solving unit, and the target light signal includes the reference light signal or the measurement light signal received by the dual-frequency signal processing unit; The solving unit adjusts the optical signal conversion gain in real time through the temperature value and the DC component of the voltage signal, and determines the displacement of the device under test on the target axis corresponding to the measuring optical signal through the AC components of the voltage signal corresponding to the reference optical signal and the measuring optical signal, respectively. The target axis refers to a moving axis on which the device under test moves under multiple moving axes, and one moving axis corresponds to a dual-frequency signal processing unit that receives the measuring optical signal; The frequency synchronization control unit sends a frequency signal to each dual-frequency signal processing unit to synchronize the sampling frequency through the frequency signal; The auxiliary unit eliminates interference by converting the electric energy of the external power supply into the first power supply required by the dual-frequency signal processing unit and the second power supply required by the frequency synchronization control unit, and providing different grounding terminals to the dual-frequency signal processing unit and the frequency synchronization control unit.

2. The processing card according to claim 1, characterized in that: The processing card further includes a cascade module, which is used to connect other processing cards. For each dual-frequency signal processing unit, the dual-frequency signal processing unit includes a conversion module. Among them, multiple processing cards are connected in sequence through the cascade module, and the multiple processing cards include a main processing card and at least one slave processing card. The conversion module of the first dual-frequency signal processing unit among the multiple dual-frequency signal processing units of the main processing card receives the reference light signal emitted by the dual-frequency laser interferometer and converts the reference light signal into a reference voltage signal. The other dual-frequency signal processing units of the main processing card and each dual-frequency signal processing unit in at least one slave processing card serve as the second dual-frequency signal processing unit. The conversion module of the first dual-frequency signal processing unit receives the reference light signal of the reference axis corresponding to the dual-frequency laser interferometer and converts the reference light signal into the reference voltage signal, and sends it to the cascade module of the slave processing card connected to it through the cascade module of the main processing card, so that each slave processing card connected in sequence forwards the reference voltage signal one by one. The conversion module of the second dual-frequency signal processing unit receives the measurement light signal of the target axis corresponding to the dual-frequency laser interferometer and converts the measurement light signal into a measurement voltage signal. Among them, the conversion module includes a high-voltage circuit, an avalanche photodiode and a voltage conversion circuit. The avalanche photodiode is arranged between the high-voltage circuit and the voltage conversion circuit. The high-voltage circuit provides a reverse bias voltage to the avalanche photodiode. The avalanche photodiode is used to convert the collected reference light signal or measurement light signal emitted by the dual-frequency laser interferometer into a corresponding current signal. The voltage conversion circuit is used to convert the current signal corresponding to the reference light signal into a reference voltage signal or convert the current signal corresponding to the measurement light signal into a measurement voltage signal.

3. The processing card according to claim 2, characterized in that: The solution unit includes a solution module. For each dual-frequency signal processing unit, the dual-frequency signal processing unit also includes a separation module, a first multi-way selection module, a first analog-to-digital conversion module and a signal conversion module. The first multi-way selection module includes a temperature collector. The temperature collector is used to collect the temperature value of the avalanche photodiode of the conversion module of the dual-frequency signal processing unit. The separation module is connected to the conversion module and the cascade module of the dual-frequency signal processing unit, and the voltage signals respectively output by the conversion module and the cascade module are parsed into the DC component and the AC component. The first multi-way selection module sends the temperature value and the DC component to the first analog-to-digital conversion module respectively. The first analog-to-digital conversion module converts the temperature value into a temperature digital signal and converts the DC component into a DC digital signal, and then sends the temperature digital signal and the DC digital signal to the resolution module one by one. The solution module determines a voltage adjustment digital signal for real-time adjustment of the optical signal conversion gain based on the temperature digital signal and the DC digital signal, and the signal conversion module determines a voltage adjustment analog signal for the high-voltage circuit of the conversion module based on the voltage adjustment digital signal, so that the high-voltage circuit provides the reverse bias voltage to the avalanche photodiode based on the voltage adjustment analog signal.

4. The processing card according to claim 3, characterized in that: For each dual-frequency signal processing unit, the dual-frequency signal processing unit further includes a second multi-channel selection module and a second analog-to-digital conversion module, wherein the second multi-channel selection module includes a digital frequency synthesizer, and the digital frequency synthesizer is used to simulate a measurement signal corresponding to the measurement optical signal or a reference signal corresponding to the reference optical signal; Wherein, the second multi-channel selection module sends the AC component output by the separation module to the second analog-to-digital conversion module, the second analog-to-digital conversion module converts the AC component into an AC digital signal, and the solution module determines the displacement on the target axis according to the AC digital signal; Alternatively, the second multi-channel selection module sends the measurement signal or the reference signal to the second analog-to-digital conversion module, the second analog-to-digital conversion module converts the measurement signal or the reference signal into digital signals for self-test, and the solution module performs self-test based on the digital signals.

5. The processing card according to claim 4, characterized in that: For each dual-frequency signal processing unit, the dual-frequency signal processing unit further includes a first single-ended to differential conversion module and a second single-ended to differential conversion module. The first single-ended to differential conversion module is disposed between the first multi-channel selection module and the first analog-to-digital conversion module, and is used to convert the temperature value into a temperature differential signal or convert the DC component into a DC differential signal, so that the first analog-to-digital conversion module converts the temperature differential signal into a temperature digital signal or converts the DC differential signal into a DC digital signal. The second single-ended to differential module is arranged between the second multi-way selection module and the second analog-to-digital conversion module, and is used to convert the measurement signal or the reference signal into an analog differential signal, or to convert the AC component into an AC differential signal, so that the second analog-to-digital conversion module converts the analog differential signal into a digital signal for self-test or converts the AC differential signal into an AC digital signal.

6. The processing card according to claim 1, characterized in that: The frequency synchronization control unit includes a reference frequency generation module, a frequency synchronization module and a differential driver. The working modules of the frequency synchronization control units corresponding to the master processing card and each slave processing card are different. The working module of the frequency synchronization control unit of the master processing card is the reference frequency generation module, and the working module of the frequency synchronization control unit of each slave processing card is the frequency synchronization module. The frequency signal includes a reference frequency signal sent by the reference frequency generation module and a synchronization frequency signal sent by the frequency synchronization control unit. The reference frequency generation module sends the reference frequency signal to each dual-frequency signal processing unit of the master processing card through the differential driver, and the reference frequency generation module sends the reference frequency signal to the frequency synchronization control unit of each slave processing card. The frequency synchronization control unit sends the synchronization frequency signal to each dual-frequency signal processing unit of the slave processing card to which it belongs through the differential driver according to the reference frequency signal.

7. The processing card according to claim 6, characterized in that: The reference frequency generation module includes a first oscillator and a first clock distributor. Among them, the first oscillator inputs the first initial frequency signal to the first clock distributor, the first clock distributor splits the first initial frequency signal into a first reference frequency signal and a second reference frequency signal through clock distribution, sends the first reference frequency signal to the differential driver, sends the second reference frequency signal to the frequency synchronization control unit of each slave processing card, and the differential driver sends the first reference frequency signal to each dual-frequency signal processing unit of the master processing card.

8. The processing card according to claim 6, characterized in that: The frequency synchronization module includes a second oscillator, a second clock distributor, a phase detector and a proportional integral circuit. Among them, the second oscillator inputs the second initial frequency signal to the second clock distributor, the second clock distributor splits the second initial frequency signal into a first synchronous frequency signal and a second synchronous frequency signal through clock distribution, sends the first synchronous frequency signal to the differential driver, sends the second synchronous frequency signal to the phase detector, the differential driver sends the first synchronous frequency signal to each dual-frequency signal processing unit of the slave processing card, the phase detector outputs a phase difference signal to the proportional integration circuit by comparing the second basic frequency signal and the second synchronous frequency signal, and the proportional integration circuit determines the control voltage applied to the second oscillator through the phase difference signal, so that the second oscillator outputs the first synchronous frequency signal with the same frequency as the first basic frequency signal according to the control voltage.

9. The processing card according to claim 7, characterized in that: The first oscillator includes a programmable oscillator or a resolution module in the first dual-frequency signal processing unit of the main processing card.

10. The processing card according to claim 1, characterized in that: The processing card also includes a communication interface and an indicator light. The communication interface is used to connect to a host computer. Among them, the solving unit transmits the displacement of each dual-frequency signal processing unit corresponding to the reference light signal on the target axis to the host computer through the communication interface, and receives the reference voltage signal or the measurement voltage signal determined by each dual-frequency signal processing unit to determine whether the light intensity is in an abnormal state. If the light intensity is in an abnormal state, the indicator light prompts that it is in an abnormal state.

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