A method and device for directly collecting signals with adaptive adjustment of filtering bandwidth in a terahertz system

Abstract

The present invention discloses a method and device for directly collecting signals with adaptive adjustment of filtering bandwidth in a terahertz system. The weak terahertz current signal generated by a detecting photoconductive antenna is amplified, offset, filtered, quantized, collected, and signal-processed in sequence through a preamplifier unit, an offset circuit unit, a filter unit, an ADC analog-to-digital conversion unit, and an FPGA unit. Finally, the processed signal is uploaded to a host computer control software to achieve the collection of terahertz signals. In addition to dynamically and adaptively adjusting the filtering bandwidth of the filter, it can also adjust the amplification factor of the signal online, reduce the interference of noise on the terahertz signal in real time, and improve the dynamic range of the system.

Description

Technical Field:

[0001] The present invention belongs to the technical fields of terahertz time-domain spectroscopy and terahertz tomography, and particularly relates to a method and device for directly collecting signals with an adaptively adjusted filtering bandwidth in a terahertz system. Background Art:

[0002] Terahertz waves are electromagnetic waves with frequencies between 0.1 and 10 THz (1 THz = 10 12 Hz), lying between microwave and infrared waves. Due to their unique penetrability, high security, and fingerprint spectrum characteristics, terahertz waves are widely used in fields such as material identification, security inspection, non-destructive testing of materials and structures, in-vivo inspection of biological tissues, and wireless communication.

[0003] With the gradual application of terahertz technology in the industrial field, higher requirements have been put forward for the acquisition speed of terahertz signals. The speed of obtaining terahertz signals by the original stepping motor-based delay line scheme can no longer meet the needs of industrial applications. More and more systems use schemes such as oscillating motors or rotating motors with mechanical structures to obtain terahertz signals. The signal acquisition scheme of the commonly used lock-in amplifier can no longer meet the requirements of the system sampling rate. Therefore, a direct signal acquisition scheme is adopted to achieve the acquisition of terahertz signals in the system.

[0004] Affected by the material and structure of the photoconductive detection antenna itself, the terahertz photocurrent signal is very weak, with a magnitude of only dozens to hundreds of pA, and is extremely easy to be submerged in noise. In order to achieve precise detection of terahertz signals, we need to extract, recover, and enhance the measured signal from the noise. Therefore, the precise detection of such weak terahertz signals has become a key part of the terahertz system.

[0005] To improve the dynamic range of the terahertz system, the bandwidth of the low-pass filter in the direct signal acquisition circuit is designed according to the bandwidth of the acquired signal, and the oscillation or rotation frequency of the mechanical structure-based delay line determines the signal bandwidth of the detected photocurrent in the terahertz system. During the use of the terahertz system, users usually adjust the scanning range and oscillation or rotation frequency of the delay line according to the characteristics of the test sample. To improve the dynamic range of the system, the present invention proposes a method and device for directly collecting signals with an adaptively adjusted filtering bandwidth. Summary of the Invention:

[0006] The purpose of the present invention is to overcome the shortcomings of the existing technology and seek to design a method and device for directly collecting signals with an adaptively adjusted filtering bandwidth in a terahertz system.

[0007] To achieve the above object, a signal direct acquisition device for adaptively adjusting the filtering bandwidth in a terahertz system according to the present invention includes a signal input interface, a pre - current amplifier unit, a bias adjustment circuit unit, a filter unit, an ADC analog - to - digital conversion unit, an FPGA unit, a filtering bandwidth adjustment circuit unit, and a host computer communication interface. Among them, the FPGA unit includes a filtering bandwidth adaptive configuration module and a linear cumulative average processing module; the input end of the signal input interface is externally connected to the detection antenna of the terahertz spectroscopy and imaging system; the pre - current amplifier unit is connected to the output end of the input interface to amplify the terahertz photocurrent signal and convert it into a voltage signal; the input end of the bias adjustment circuit unit is connected to the output end of the pre - current amplifier unit to bias the signal input by the pre - current amplifier unit; the input end of the filter unit is connected to the output end of the bias adjustment circuit unit. The filtering bandwidth of the filter unit is dynamically and adaptively configured by two unit modules, namely the filtering bandwidth adaptive configuration module and the filtering bandwidth adjustment circuit unit, after the system works, to filter out the out - of - band noise of the input signal and improve the signal - to - noise ratio of the input signal; the input end of the ADC analog - to - digital conversion unit is connected to the output end of the filter unit to sample, hold, quantize, and encode the input signal of the filter unit and convert the analog signal into a digital signal; the input end of the FPGA unit is connected to the output end of the ADC analog - to - digital conversion unit. Among them, the input end of the filtering bandwidth adaptive configuration module is connected to the output end of the ADC analog - to - digital conversion unit. The filtering bandwidth adaptive configuration module dynamically adjusts the filtering bandwidth of the filtering bandwidth adjustment circuit unit according to the processing result of the input signal to select the optimal filtering bandwidth for the terahertz system; the input end of the linear cumulative average processing module in the FPGA unit is connected to the output end of the filtering bandwidth adaptive configuration module. After the system adapts to the optimal filtering bandwidth, the linear cumulative average processing module processes the input signal through the linear cumulative average algorithm to filter out the interference of white noise in the system to the signal; the host computer communication interface is connected to the output end of the FPGA unit to interact information with the host computer through the host computer communication interface; the filtering bandwidth adjustment circuit unit is respectively connected to the filtering bandwidth adaptive configuration module and the filter unit. The filtering bandwidth adjustment circuit unit dynamically adjusts the filtering bandwidth of the filter unit according to the bandwidth parameters configured by the filtering bandwidth adaptive configuration module to achieve the optimal filtering of the current system.

[0008] Furthermore, a signal direct acquisition device for adaptively adjusting the filtering bandwidth in a terahertz system according to the present invention further includes a gain adjustment circuit unit. Correspondingly, the FPGA unit further includes a gain configuration module. The gain adjustment circuit unit is respectively connected to the gain configuration module and the pre - current amplifier unit. The gain configuration module is used to configure gain parameters, and the gain adjustment circuit unit configures the gain amplification factor of the pre - current amplifier unit based on the gain parameters.

[0009] Further explanation, a signal direct acquisition device for adaptively adjusting the filtering bandwidth in a terahertz system according to the present invention, the FPGA unit further includes an offset configuration module, the output end of the offset configuration module is connected to the offset circuit unit, and the offset configuration module is used to configure the offset circuit unit to output different offset voltages.

[0010] Further explanation, the FPGA unit according to the present invention further includes other function management modules, and the other function management module 605 is used for communication, monitoring, configuration and management of the bias voltage source module and the delay line circuit module in the terahertz system.

[0011] Further explanation, a signal direct acquisition device for adaptively adjusting the filtering bandwidth in a terahertz system according to the present invention further includes an MCU unit, and the MCU unit is used for configuring and monitoring the femtosecond laser module.

[0012] Further explanation, a signal direct acquisition device for adaptively adjusting the filtering bandwidth in a terahertz system according to the present invention further includes a power supply unit, and the power supply unit is used to provide power and power-on timing management function for the signal direct acquisition device.

[0013] Further explanation, a signal direct acquisition device for adaptively adjusting the filtering bandwidth in a terahertz system according to the present invention further includes an analog output interface, and the analog output interface is connected to the output end of the filter unit for outputting the acquired terahertz analog signal.

[0014] Further explanation, a signal direct acquisition device for adaptively adjusting the filtering bandwidth in a terahertz system according to the present invention further includes a peripheral circuit interface, and the peripheral circuit interface is a communication interface for the femtosecond laser module, the delay line circuit module, the bias voltage source module, the status monitoring module, the status display module and the signal direct acquisition device.

[0015] A method for directly acquiring signals with adaptively adjusted filtering bandwidth in a terahertz system according to the present invention specifically includes the following steps:

[0016] (1) The terahertz signal photocurrent enters the preamplifier unit through the signal input interface, and the preamplifier unit amplifies the signal based on the gain amplification factor and converts it into a voltage signal;

[0017] (2) The amplified signal enters the offset circuit unit, and the offset circuit unit offsets the signal input by the preamplifier unit based on the bias parameters;

[0018] (3) The offset signal enters the filter unit, and the filter unit filters out the out-of-band noise of the sampled signal based on the filtering bandwidth, which can improve the signal-to-noise ratio of the signal;

[0019] (4) One path of the filtered signal is output through the analog output interface. The output is an analog signal, which facilitates users to analyze and process data.

[0020] (5) The other path of the filtered signal is input into the ADC analog-to-digital conversion unit. The ADC analog-to-digital conversion unit realizes sampling, holding, quantization, and encoding of the terahertz signal, and converts the analog signal into a digital signal.

[0021] (6) When the output signal of the ADC analog-to-digital conversion unit enters the FPGA unit, it first enters the filter bandwidth adaptive configuration module. After the terahertz system is powered on, when signal acquisition is performed for the first time or when data acquisition is performed after changing the oscillation or rotation frequency of the delay line through the host computer, if the optimal filter bandwidth is not determined at this time, the signal is processed in the filter bandwidth adaptive configuration module, and at the same time, the optimal filter bandwidth in the current system is adaptively configured through the filter bandwidth adjustment circuit unit. The data at this time will not be transmitted to the lower-level module.

[0022] (7) After the optimal filter bandwidth is determined, the signal uploaded by the ADC analog-to-digital conversion unit will pass through the filter bandwidth adaptive configuration module and be transparently transmitted into the linear accumulation and averaging processing module. The signal is processed in the linear accumulation and averaging processing module through the linear accumulation and averaging algorithm.

[0023] (8) The signal processed by the linear accumulation and averaging processing module uploads the data to the host computer through the host computer communication interface. Users can choose to analyze and process the data through the host computer, or export the data through the host computer and analyze and process it by themselves.

[0024] Further, in step (1), after the terahertz system is powered on, the gain configuration module inputs the default gain parameter to the gain adjustment circuit unit. During use, the gain configuration module inputs the adjusted gain parameter to the gain adjustment circuit unit in real time based on the instruction of the host computer. The gain adjustment circuit unit inputs the gain amplification factor to the preamplifier current amplifier unit in real time based on the received gain parameter. The default gain amplification factor of the preamplifier current amplifier unit is 10 ^6 , and the gain amplification factors that the gain adjustment circuit unit can configure are 5x10 ^5 、10 ^6 、5x10 ^6 and 10 ^7 .

[0025] Further, in step (2), when the terahertz system is powered on, the bias configuration module inputs the default bias parameter to the bias adjustment circuit unit. During the use process, the bias configuration module inputs the adjusted bias parameter to the bias adjustment circuit unit in real time based on the instruction of the host computer.

[0026] Further, in step (3), the filtering bandwidth of the filter unit is dynamically and adaptively configured by two unit modules, namely, the filtering bandwidth adaptive configuration module and the filtering bandwidth adjustment circuit unit, through a polling mechanism. According to the oscillation frequency or rotation frequency of the delay line of the mechanical structure used in the current system, the configured filtering bandwidths are 10 kHz, 20 kHz, 30 kHz, and 40 kHz.

[0027] Further explanation: After the terahertz system is powered on, when signal acquisition is performed for the first time or when data acquisition is performed after changing the oscillation or rotation frequency of the delay line through the host computer, that is, when the optimal filtering bandwidth is not determined at this time, the signal entering the filtering bandwidth adaptive configuration module 603 will be cached first, and then the accumulated average processing will be performed on the complete terahertz signal in the cache. The number of accumulated averages is 20 times, and the final result and the filtering bandwidth parameter of the filtering bandwidth adjustment circuit unit 7 configured at this time are stored; through the designed filtering bandwidth polling mechanism, the filtering bandwidth adaptive configuration module will sequentially configure the bandwidth parameters in the filtering bandwidth adjustment circuit unit, and then perform the accumulated average processing on the acquired signal and store the final result and the corresponding bandwidth parameter; when the designed filtering bandwidth polling mechanism is polled completely, the filtering bandwidth adaptive configuration module will configure the filtering bandwidth adjustment circuit unit according to the bandwidth parameter with the best signal-to-noise ratio in the stored results, and use this bandwidth as the optimal filtering bandwidth of the signal direct acquisition circuit.

[0028] Compared with the prior art, the present invention has the following beneficial effects: In addition to dynamically and adaptively adjusting the filtering bandwidth of the filter, the signal direct acquisition circuit of the present invention can also online adjust the amplification multiple of the preamplifier gain, and reduce the interference of noise on the terahertz signal in real time through the linear accumulation algorithm, improving the dynamic range of the system. The signal direct acquisition circuit supports dual-channel output of analog signals and digital signals, facilitating users to analyze and process signals. The signal direct acquisition circuit also has functions such as controlling and managing other functional components in the terahertz system. Description of the Drawings:

[0029] Figure 1 It is a schematic structural diagram of the signal direct acquisition method and device for adaptively adjusting the filtering bandwidth in the terahertz system described in Embodiment 1. Specific Embodiments:

[0030] The present invention will be further described below through specific embodiments in conjunction with the drawings.

[0031] Embodiment 1

[0032] The present invention realizes the acquisition of terahertz current signals by using the principle of direct signal sampling. Photo-generated carriers generated by femtosecond laser-excited photoconductive antennas form photocurrents under the action of terahertz pulsed electric fields. Since the magnitude of the terahertz current signal is linearly related to the intensity of the terahertz signal, the measurement of the terahertz pulse intensity can be achieved by detecting the change in current.

[0033] A direct signal acquisition device for adaptively adjusting the filtering bandwidth in a terahertz system according to this embodiment amplifies, offsets, filters, quantizes, acquires, and processes the weak terahertz current signals generated by the detection photoconductive antenna, and finally uploads the processed signals to the host computer control software to realize the acquisition of terahertz signals.

[0034] As Figure 1 shown, a direct signal acquisition device for adaptively adjusting the filtering bandwidth in a terahertz system according to this embodiment (abbreviated as the direct signal acquisition device) includes a signal input interface 1, a preamplifier unit 2, an offset circuit unit 3, a filter unit 4, an ADC analog-to-digital conversion unit 5, an FPGA unit 6, a filtering bandwidth adjustment circuit unit 7, and a host computer communication interface 12. Among them, the FPGA unit 6 includes a filtering bandwidth adaptive configuration module 603 and a linear accumulation and averaging processing module 604.

[0035] The input end of the signal input interface 1 is externally connected to the detection antenna of the terahertz spectroscopy and imaging system;

[0036] The preamplifier unit 2 is connected to the output end of the input interface 1 to amplify the terahertz photocurrent signal and convert it into a voltage signal;

[0037] The input end of the offset circuit unit 3 is connected to the output end of the preamplifier unit 2, and is used to offset the signal input by the preamplifier unit 2 to ensure that the signal input to the ADC analog-to-digital conversion unit 5 is within the input threshold range of the ADC conversion chip. After the system is powered on, the bias voltage of the offset circuit unit 3 will be configured by default;

[0038] The input end of the filter unit 4 is connected to the output end of the offset circuit unit 3. The filtering bandwidth of the filter unit 4 is dynamically configured adaptively by two unit modules, namely the filtering bandwidth adaptive configuration module 603 and the filtering bandwidth adjustment circuit unit 7, after the system works, and is used to filter out the out-of-band noise of the input signal and improve the signal-to-noise ratio of the input signal;

[0039] The input end of the ADC analog-to-digital conversion unit 5 is connected to the output end of the filter unit 4, and is used to sample, hold, quantize, and encode the input signal of the filter unit 4 and convert the analog signal into a digital signal;

[0040] The 6 input ends of the FPGA unit are connected to the output end of the ADC analog-to-digital conversion unit 5. Among them, the input end of the filtering bandwidth adaptive configuration module 603 is connected to the output end of the ADC analog-to-digital conversion unit 5. The filtering bandwidth adaptive configuration module 603 dynamically adjusts the filtering bandwidth of the filtering bandwidth adjustment circuit unit 7 according to the processing result of the input signal to select the optimal filtering bandwidth for the system;

[0041] The input end of the linear accumulation average processing module 604 in the FPGA unit 6 is connected to the output end of the filtering bandwidth adaptive configuration module 603. After the optimal filtering bandwidth is adapted by the system, the linear accumulation average processing module 604 processes the input signal through the linear accumulation average algorithm to filter out the interference of white noise on the signal in the system and further improve the dynamic range of the system;

[0042] The host computer communication interface 12 is connected to the output end of the FPGA unit 6 to perform information interaction with the host computer through the host computer communication interface 12;

[0043] The filtering bandwidth adjustment circuit unit 7 is respectively connected to the filtering bandwidth adaptive configuration module 603 and the filter unit 4. The filtering bandwidth adjustment circuit unit 7 dynamically adjusts the filtering bandwidth of the filter unit 4 according to the bandwidth parameters configured by the filtering bandwidth adaptive configuration module 603 to achieve the optimal filtering of the current system;

[0044] Furthermore, a signal direct acquisition device for adaptively adjusting the filtering bandwidth in a terahertz system according to this embodiment further includes a gain adjustment circuit unit 8. Correspondingly, the FPGA unit 6 further includes a gain configuration module 601. The gain adjustment circuit unit 8 is respectively connected to the gain configuration module 601 and the pre-current amplifier unit 2. The gain configuration module 601 is used to configure gain parameters, and the gain adjustment circuit unit 8 configures the gain amplification factor of the pre-current amplifier unit 2 based on the gain parameters. The user can independently adjust the gain amplification factor of the gain adjustment circuit unit 8 through the host computer software;

[0045] Furthermore, a signal direct acquisition device for adaptively adjusting the filtering bandwidth in a terahertz system according to this embodiment, the FPGA unit 6 further includes an offset configuration module 602. The output end of the offset configuration module 602 is connected to the offset circuit unit 3. The offset configuration module 602 is used to configure the offset circuit unit 3 to output different offset voltages. The user can independently control the offset voltage output by the offset circuit unit 3 through the offset configuration module 602 to further improve the system applicability of the signal direct acquisition device;

[0046] Further explanation, the FPGA unit 6 further includes other function management modules 605, and the other function management modules 605 are used for communicating, monitoring, configuring, and managing other function modules in the terahertz system. The other function modules include the bias voltage source module, delay line circuit module, etc. in the system;

[0047] Further explanation, an apparatus for directly collecting signals with adaptive filtering bandwidth adjustment in a terahertz system according to this embodiment further includes an MCU unit 9. The MCU unit 9 is used for configuring and monitoring other function modules in the terahertz system. The other function modules include the femtosecond laser module, etc. in the system.

[0048] Further explanation, an apparatus for directly collecting signals with adaptive filtering bandwidth adjustment in a terahertz system according to this embodiment further includes a power supply unit 10. The power supply unit 10 is used for providing power and power-on timing management functions for the signal direct collection device.

[0049] Further explanation, an apparatus for directly collecting signals with adaptive filtering bandwidth adjustment in a terahertz system according to this embodiment further includes an analog output interface 11. The analog output interface 11 is connected to the output end of the filter unit 4 and is used for outputting the collected terahertz analog signal to facilitate users to perform data analysis and processing.

[0050] Further explanation, an apparatus for directly collecting signals with adaptive filtering bandwidth adjustment in a terahertz system according to this embodiment further includes a peripheral circuit interface 13. The peripheral circuit interface 13 is a communication interface between other function modules in the terahertz system and the signal direct collection device. The other function modules include the femtosecond laser module, delay line circuit module, bias voltage source module, status monitoring module, status display module, etc. The other function modules can communicate, monitor, configure, and manage through the other function management module 605 in the FPGA unit 6 and the MCU unit 9 together;

[0051] Specifically, the minimum signal that the preamplifier unit 2 can recognize is a sub-pA level current signal, and the default gain amplification factor of the preamplifier unit 2 is 10 ^6 。

[0052] A method for directly collecting signals with adaptive filtering bandwidth adjustment in a terahertz system according to the present invention specifically includes the following steps:

[0053] (1) The terahertz signal photocurrent enters the preamplifier unit 2 through the signal input interface 1. The preamplifier unit amplifies the signal based on the gain amplification factor and converts it into a voltage signal. The minimum signal that the designed preamplifier unit 2 can recognize is a sub-pA level current signal.

[0054] After the terahertz system is powered on, the gain configuration module 601 will default-configure the gain multiple of the gain adjustment circuit unit 8. The user can input four set amplification multiples online (through the host computer). The gain configuration module 601 will convert the gain amplification multiple into corresponding parameters to configure the gain adjustment circuit unit 8, so as to configure the amplification multiple for the preamplifier current unit 2. Specifically, the default gain amplification multiple of the preamplifier current unit 2 is 10 ^6 , and the configurable gain amplification multiples of the gain adjustment circuit unit 8 are 5x10 ^5 , 10 ^6 , 5x10 ^6 , and 10 ^7 .

[0055] After the terahertz system is powered on, the gain configuration module 601 inputs the default gain parameter to the gain adjustment circuit unit 8. During use, the gain configuration module 601 inputs the adjusted gain parameter to the gain adjustment circuit unit 8 in real time based on the instruction of the host computer. The gain adjustment circuit unit 8 inputs the gain amplification multiple to the preamplifier current unit 2 in real time based on the received gain parameter.

[0056] (2) The amplified signal enters the bias adjustment circuit unit 3, and the bias adjustment circuit unit 3 biases the signal input by the preamplifier current unit based on the bias parameter.

[0057] After the terahertz system is powered on, it will default-configure the bias voltage. The user can also adjust the bias voltage online through the bias configuration module 602 in the host computer.

[0058] When the terahertz system is powered on, the bias configuration module 602 inputs the default bias parameter to the bias adjustment circuit unit 3. During the use process, the bias configuration module 602 inputs the adjusted bias parameter to the bias adjustment circuit unit 3 in real time based on the instruction of the host computer.

[0059] (3) The signal after bias adjustment enters the filter unit 4. The filter unit 4 is a 4th-order Butterworth low-pass filter designed based on the Sallen-key circuit. The filter unit 4 filters out the out-of-band noise of the sampled signal based on the filter bandwidth, which can improve the signal-to-noise ratio of the signal.

[0060] The filter bandwidth of the filter unit 4 is dynamically and adaptively configured by two unit modules, the filter bandwidth adaptive configuration module 603 and the filter bandwidth adjustment circuit unit 7, through a polling mechanism. According to the oscillation frequency or rotation frequency of the delay line of the mechanical structure currently used in the system, the configured filter bandwidths are 10 kHz, 20 kHz, 30 kHz, and 40 kHz.

[0061] (4) One path of the filtered signal is output through the analog output interface 11, and the output is an analog signal, which is convenient for users to analyze and process data;

[0062] (5) Another path of the filtered signal is input into the ADC analog-to-digital conversion unit 5. The ADC analog-to-digital conversion unit 5 realizes sampling, holding, quantization, and encoding of the terahertz signal, and converts the analog signal into a digital signal.

[0063] (6) When the output signal of the ADC analog-to-digital conversion unit 5 enters the FPGA unit 6, it first enters the filter bandwidth adaptive configuration module 603. After the terahertz system is powered on, when signal acquisition is performed for the first time or when data acquisition is performed after changing the oscillation or rotation frequency of the delay line through the host computer, and the optimal filter bandwidth is not determined at this time, the signal is processed in the filter bandwidth adaptive configuration module 603. At the same time, the filter bandwidth adjustment circuit unit 7 adaptively configures the optimal filter bandwidth in the current system, and the data at this time will not be transmitted to the lower-level module.

[0064] (7) After the optimal filter bandwidth is determined, the signal uploaded by the ADC analog-to-digital conversion unit 5 will pass through the filter bandwidth adaptive configuration module 603 and be transparently transmitted to the linear cumulative average processing module 604. The signal is processed in the linear cumulative average processing module 604 through the linear cumulative average algorithm to filter out the interference of white noise in the system to the signal and further improve the dynamic range of the terahertz system.

[0065] (8) The signal processed by the linear cumulative average processing module 604 uploads the data to the host computer through the host computer communication interface 12. The user can choose to analyze and process the data through the host computer, or export the data through the host computer and analyze and process it by himself.

[0066] (9) The peripheral circuit interface 13 is the communication interface between other functional modules in the system and the signal direct acquisition circuit for adaptively adjusting the filter bandwidth. Other functional modules in the system can communicate, monitor, configure, and manage through other functional management modules 605 and the MCU unit 9 in the FPGA unit 6.

[0067] Further explanation: When the signal sampled by the ADC analog-to-digital conversion unit 5 enters the FPGA unit 6, it first enters the filter bandwidth adaptive configuration module 603.

[0068] Further explanation: After the terahertz system is powered on, when signal acquisition is performed for the first time or when data acquisition is performed after changing the oscillation or rotation frequency of the delay line through the host computer, that is, when the optimal filter bandwidth is not determined at this time, the signal entering the filter bandwidth adaptive configuration module 603 will be cached first, and then the accumulated average processing will be performed on the complete cached terahertz signal. The number of accumulated averages is 20 times, and the final result and the filter bandwidth parameter of the filter bandwidth adjustment circuit unit 7 configured at this time will be stored.

[0069] Further explanation, through the designed filtering bandwidth polling mechanism, the filtering bandwidth adaptive configuration module 603 will sequentially configure the bandwidth parameters in the filtering bandwidth adjustment circuit unit 7, then perform cumulative averaging processing on the collected signals and store the final results and the corresponding bandwidth parameters.

[0070] Further explanation, when the designed filtering bandwidth polling mechanism is polled completely, the filtering bandwidth adaptive configuration module 603 will configure the filtering bandwidth adjustment circuit unit 7 according to the bandwidth parameter with the best signal-to-noise ratio in the stored results, and use this bandwidth as the optimal filtering bandwidth of the signal direct acquisition circuit.

[0071] Further explanation, when the optimal filtering bandwidth is determined, that is, after the filtering bandwidth adaptive configuration module 603 completes the bandwidth configuration, it will discard the previously stored data and transmit the newly received signals to the linear cumulative averaging processing module 604.

[0072] Further explanation, the linear cumulative averaging processing module 604 uses the linear cumulative averaging algorithm to process the received signals, filters out the Gaussian noise in the system superimposed on the received signals, and further improves the dynamic range of the system.

[0073] Further explanation, considering the timeliness of the system operation and the improvement result of the signal-to-noise ratio comprehensively, according to the system simulation and actual test results, the cumulative number of times in the linear cumulative averaging processing module 604 is default set to 50 times, and the cumulative number of times supports online configuration by users.

[0074] In addition to dynamically and adaptively adjusting the filtering bandwidth of the filter, the signal direct acquisition circuit of the present invention can also online adjust the amplification factor of the pre-amplifier gain of the current, reduce the interference of noise on the terahertz signal in real time through the linear cumulative algorithm, and improve the dynamic range of the system. The signal direct acquisition circuit supports dual-channel output of analog signals and digital signals, which is convenient for users to analyze and process signals. The signal direct acquisition circuit also has functions such as controlling and managing other functional components in the terahertz system.

Claims

1. A signal direct acquisition device for adaptively adjusting the filtering bandwidth in a terahertz system, characterized in that, It includes a signal input interface, a pre - current amplifier unit, a bias adjustment circuit unit, a filter unit, an ADC analog - to - digital conversion unit, an FPGA unit, a filter bandwidth adjustment circuit unit, and a host computer communication interface. Among them, the FPGA unit includes a filter bandwidth adaptive configuration module and a linear cumulative average processing module; the input end of the signal input interface is externally connected to the detection antenna of the terahertz spectroscopy and imaging system; the pre - current amplifier unit is connected to the output end of the input interface to amplify the terahertz photocurrent signal and convert it into a voltage signal; the input end of the bias adjustment circuit unit is connected to the output end of the pre - current amplifier unit to bias the signal input by the pre - current amplifier unit; the input end of the filter unit is connected to the output end of the bias adjustment circuit unit. The filter bandwidth of the filter unit is dynamically and adaptively configured by two unit modules, namely the filter bandwidth adaptive configuration module and the filter bandwidth adjustment circuit unit, after the system works, to filter out the out - of - band noise of the input signal and improve the signal - to - noise ratio of the input signal; the input end of the ADC analog - to - digital conversion unit is connected to the output end of the filter unit to sample, hold, quantize, and encode the input signal of the filter unit and convert the analog signal into a digital signal; the input end of the FPGA unit is connected to the output end of the ADC analog - to - digital conversion unit. Among them, the input end of the filter bandwidth adaptive configuration module is connected to the output end of the ADC analog - to - digital conversion unit. The filter bandwidth adaptive configuration module dynamically adjusts the filter bandwidth of the filter bandwidth adjustment circuit unit according to the processing result of the input signal to select the optimal filter bandwidth for the terahertz system; the input end of the linear cumulative average processing module in the FPGA unit is connected to the output end of the filter bandwidth adaptive configuration module. After the system adapts to the optimal filter bandwidth, the linear cumulative average processing module processes the input signal through the linear cumulative average algorithm to filter out the interference of white noise in the system to the signal; the host computer communication interface is connected to the output end of the FPGA unit to interact with the host computer through the host computer communication interface; the filter bandwidth adjustment circuit unit is respectively connected to the filter bandwidth adaptive configuration module and the filter unit. The filter bandwidth adjustment circuit unit dynamically adjusts the filter bandwidth of the filter unit according to the bandwidth parameters configured by the filter bandwidth adaptive configuration module to achieve the optimal filtering of the current system.

2. The signal direct acquisition device for adaptively adjusting the filtering bandwidth in the terahertz system according to claim 1, characterized in that, It further includes a gain adjustment circuit unit. Correspondingly, the FPGA unit further includes a gain configuration module. The gain adjustment circuit unit is respectively connected to the gain configuration module and the pre - current amplifier unit. The gain configuration module is used to configure the gain parameters, and the gain adjustment circuit unit configures the gain amplification factor of the pre - current amplifier unit based on the gain parameters.

3. The signal direct acquisition device for adaptively adjusting the filtering bandwidth in the terahertz system according to claim 1, wherein The FPGA unit further includes a bias configuration module. The output end of the bias configuration module is connected to the bias adjustment circuit unit. The bias configuration module is used to configure different bias voltages output by the bias adjustment circuit unit.

4. The signal direct acquisition device for adaptively adjusting the filtering bandwidth in the terahertz system according to claim 1, wherein The FPGA unit further includes other function management modules, which are used to communicate with, monitor, configure, and manage the bias voltage source module and the delay line circuit module in the terahertz system. The direct signal acquisition method and device for adaptively adjusting the filtering bandwidth in the terahertz system further include an MCU unit and a peripheral circuit interface. The MCU unit is used to configure and monitor the femtosecond laser module, and the peripheral circuit interface is the communication interface for the femtosecond laser module, the delay line circuit module, the bias voltage source module, the status monitoring module, the status display module, and the direct signal acquisition device.

5. The signal direct acquisition device for adaptively adjusting the filtering bandwidth in the terahertz system according to claim 1, wherein It further includes a power supply unit, which is used to provide power and power-on timing management function for the direct signal acquisition device.

6. The signal direct acquisition device for adaptively adjusting the filtering bandwidth in the terahertz system according to claim 1, wherein It further includes an analog output interface, which is connected to the output end of the filter unit and is used to output the acquired terahertz analog signal.

7. A direct signal acquisition method for adaptively adjusting the filtering bandwidth in a terahertz system, characterized in that, It includes the following steps: (1) The terahertz signal photocurrent enters the pre-amplifier unit through the signal input interface, and the pre-amplifier unit amplifies the signal based on the gain amplification factor and converts it into a voltage signal. (2) The amplified signal enters the bias circuit unit, and the bias circuit unit biases the signal input by the pre-amplifier unit based on the bias parameter. (3) The biased signal enters the filter unit, and the filter unit filters out the out-of-band noise of the sampled signal based on the filtering bandwidth, which can improve the signal-to-noise ratio of the signal. (4) One path of the filtered signal is output through the analog output interface as an analog signal, which is convenient for users to analyze and process the data. (5) The other path of the filtered signal is input to the ADC analog-to-digital conversion unit, and the ADC analog-to-digital conversion unit realizes the sampling, holding, quantization, and encoding of the terahertz signal, and converts the analog signal into a digital signal. (6) When the output signal of the ADC analog-to-digital conversion unit enters the FPGA unit, it first enters the filtering bandwidth adaptive configuration module. After the terahertz system is powered on, when the signal is first acquired or when data is acquired after changing the oscillation or rotation frequency of the delay line through the host computer, and the optimal filtering bandwidth is not determined at this time, the signal is processed in the filtering bandwidth adaptive configuration module, and at the same time, the optimal filtering bandwidth in the current system is adaptively configured through the filtering bandwidth adjustment circuit unit, and the data at this time will not be transmitted to the lower-level module. (7) When the optimal filtering bandwidth is determined, the signal uploaded by the ADC analog-to-digital conversion unit will pass through the filtering bandwidth adaptive configuration module and be transparently transmitted to the linear accumulation and averaging processing module, and the signal is processed by the linear accumulation and averaging algorithm in the linear accumulation and averaging processing module. (8) The signal processed by the linear accumulation and averaging processing module uploads the data to the host computer through the host computer communication interface. The user can choose to analyze and process the data through the host computer, or export the data through the host computer and analyze and process it by himself.

8. The method for directly collecting signals with adaptive adjustment of filtering bandwidth in the terahertz system according to claim 7, characterized in that In step (1), after the terahertz system is powered on, the gain configuration module inputs the default gain parameters to the gain adjustment circuit unit. During use, the gain configuration module inputs the adjusted gain parameters to the gain adjustment circuit unit in real time based on the instructions from the host computer. The gain adjustment circuit unit inputs the gain amplification factor to the preamplifier unit in real time based on the received gain parameters. The default gain amplification factor of the preamplifier unit is 10 ^6 , and the gain amplification factors that the gain adjustment circuit unit can configure are 5x10 ^5 , 10 ^6 , 5x10 ^6 , and 10 ^7 .

9. The method for directly collecting signals with adaptive adjustment of filtering bandwidth in the terahertz system according to claim 8, characterized in that, In step (2), when the terahertz system is powered on, the bias configuration module inputs the default bias parameter to the bias circuit unit. During use, the bias configuration module inputs the adjusted bias parameter to the bias circuit unit in real time based on the instruction of the host computer.

10. The method for directly collecting signals with adaptive adjustment of filtering bandwidth in the terahertz system according to claim 9, wherein In step (3), after the terahertz system is powered on, when data acquisition is performed for the first time or when data acquisition is performed after changing the oscillation or rotation frequency of the delay line through the host computer, that is, when the optimal filtering bandwidth is not determined at this time, the signal will be cached first when entering the filtering bandwidth adaptive configuration module (603), and then the accumulated average processing will be performed on the cached complete terahertz signal. The number of accumulated averages is 20 times, and the final result and the filtering bandwidth parameter of the filtering bandwidth adjustment circuit unit (7) configured at this time are stored; through the designed filtering bandwidth polling mechanism, the filtering bandwidth adaptive configuration module will sequentially configure the bandwidth parameters in the filtering bandwidth adjustment circuit unit, and then perform the accumulated average processing on the acquired signal and store the final result and the corresponding bandwidth parameter; when the designed filtering bandwidth polling mechanism is polled, the filtering bandwidth adaptive configuration module will configure the filtering bandwidth adjustment circuit unit according to the bandwidth parameter with the best signal-to-noise ratio in the stored results, and use this bandwidth as the optimal filtering bandwidth of the signal direct acquisition circuit. The configured filtering bandwidths are 10 kHz, 20 kHz, 30 kHz, and 40 kHz.

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