A weak infrared signal processing and collecting device

Abstract

The application discloses a weak infrared signal processing and collecting device, and the infrared detector front-end preamplifier circuit comprises a bias circuit, a signal amplifier circuit and a filter conditioning circuit; the collecting circuit comprises an equal optical path difference detection circuit, an FPGA main control circuit and an ADC collecting circuit, the bias circuit is located at the front end of the infrared detector, the signal amplifier circuit is located at the rear end of the infrared detector, the filter conditioning circuit is used for filtering and processing the amplified infrared interference signal, the equal optical path difference detection circuit is used for converting the input laser interference signal into a square wave signal, the FPGA main control circuit provides the upper and lower edges of the square wave signal as a collecting trigger signal to the ADC collecting circuit, and the ADC collecting circuit is used for converting the collected infrared interference signal into a digital signal and sending the digital signal to the FPGA main control circuit. The device makes the infrared detector have higher responsivity, is suitable for more types of infrared detectors, saves the lower computer processing chip resources and improves the data processing efficiency.

Description

Technical Field

[0001] This invention relates to the field of infrared spectrometer technology, and in particular to a weak infrared signal processing and acquisition device. Background Technology

[0002] Telemetry-based Fourier transform infrared (FTIR) spectrometers typically perform real-time detection and identification of targets in an open optical path. Infrared signals are extremely weak and have high modulation frequencies; therefore, photoconductive mercury cadmium telluride (HCdT) detectors, known for their fast response and high detectivity, are commonly used. Under illumination, semiconductor materials absorb photon energy greater than their bandgap, exciting electron-hole pairs, increasing conductivity, reducing resistance, and creating the photoconductive effect. Photoconductive detectors utilize this effect, generating a linearly changing photocurrent as the output signal under an applied bias power supply. In FTIR spectrometers, the infrared detector receives weak infrared interference signals, generating microampere-level current changes. Therefore, a high-bandwidth, low-noise, and highly stable signal processing method is required. Since the raw signal acquired by the infrared detector in a FTIR spectrometer is an infrared interference signal, data from areas with equal optical path differences must be obtained. A fast Fourier transform (FFT) is then performed to obtain the infrared spectrum. Therefore, a stable and accurate equal optical path difference sampling circuit is essential for ADC (Analog-to-Differential Acquisition) data acquisition.

[0003] In existing commercial infrared detector preamplifier modules, the bias circuit often uses a simple constant voltage bias circuit, and the primary signal amplification circuit generally uses an IV transimpedance amplifier circuit, followed by subsequent amplification to obtain the test signal. The acquisition circuit uses an oversampling method to simultaneously acquire the laser and infrared interference signals to the host computer. The host computer program then finds the zero-crossing point of the laser signal, obtains equal optical path difference sampling points on the infrared interference signal through the zero-crossing point, and then performs a Fourier transform to obtain the infrared spectral data.

[0004] However, the existing technical solutions described above have the following problems: Because the internal resistance of the photoconductive infrared detector is relatively small, although the constant-voltage bias power supply is simple to design, its internal resistance changes with the incident light intensity during operation, affecting the stability of the constant-voltage bias source and reducing the detector's responsivity and signal-to-noise ratio. The commonly used IV amplification circuit can cause significant errors, mainly due to the operational amplifier output voltage being affected by bias current, offset voltage, and offset current. Furthermore, the AD oversampling method requires a dual-channel synchronous ADC chip with a high sampling rate. A high sampling rate inevitably sacrifices the number of sampling bits, reduces the signal dynamic range and signal-to-noise ratio, and consumes more main control resources, which is detrimental to real-time analysis and transmission of detection results. Summary of the Invention

[0005] The purpose of this invention is to provide a weak infrared signal processing and acquisition device. This device enables infrared detectors to have higher responsivity and is suitable for more types of infrared detectors. The designed preamplifier circuit has the advantages of low noise, high bandwidth, high gain and strong stability. It can also effectively save the resources of the lower-level machine processing chip, reduce processing time and improve data processing efficiency.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A weak infrared signal processing and acquisition device comprises an infrared detector preamplifier circuit and an acquisition circuit. The infrared detector preamplifier circuit includes a bias circuit, a signal amplification circuit, and a filtering and conditioning circuit. The acquisition circuit includes an equal optical path difference detection circuit, an FPGA main control circuit, and an ADC acquisition circuit, wherein:

[0008] The bias circuit is located at the front end of the infrared detector and is used to provide a positive constant current source bias for the infrared detector to improve the responsivity of the infrared detector.

[0009] The signal amplification circuit is located at the rear end of the infrared detector and is used to amplify the weak current signal in two stages to reduce the influence of offset voltage and thermal noise on the signal under test.

[0010] One end of the filtering and conditioning circuit is connected to the output of the signal amplification circuit, and the other end is connected to the ADC acquisition circuit. It is used to filter the infrared interference signal amplified by the signal amplification circuit and adjust it to match the voltage range input to the ADC acquisition circuit.

[0011] The equal optical path difference detection circuit is used to convert the input laser interference signal into a square wave signal and transmit the converted square wave signal to the FPGA main control circuit.

[0012] The FPGA main control circuit receives the square wave signal transmitted from the equal optical path difference detection circuit, uses the rising and falling edges of the square wave signal as acquisition trigger signals to provide the ADC acquisition circuit, provides the driving timing for the normal operation of the ADC acquisition circuit, and transmits the data returned by the ADC acquisition circuit to the host computer.

[0013] The ADC acquisition circuit is used to convert the acquired infrared interference signals at the same optical path difference position into digital signals, and send the converted signals to the FPGA main control circuit, which then sends them to the host computer.

[0014] As can be seen from the technical solution provided by the present invention, the above-mentioned device enables the infrared detector to have higher responsivity and is suitable for more types of infrared detectors. The designed preamplifier circuit has the advantages of low noise, high bandwidth, high gain and strong stability; and can effectively save the resources of the lower-level machine processing chip, reduce processing time and improve data processing efficiency. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of the structure of the weak infrared signal processing and acquisition device provided in an embodiment of the present invention;

[0017] Figure 2 This is a circuit diagram of the bias circuit and signal amplification circuit described in an embodiment of the present invention;

[0018] Figure 3 This is a schematic diagram of the circuit structure of the filter conditioning circuit described in an embodiment of the present invention;

[0019] Figure 4 This is a schematic diagram of the circuit structure of the equal optical path difference detection circuit described in an embodiment of the present invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments, and do not constitute a limitation of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0021] like Figure 1 The diagram shown is a schematic representation of a weak infrared signal processing and acquisition device provided in an embodiment of the present invention. The device comprises two parts: an infrared detector preamplifier circuit 1 and an acquisition circuit 2. The infrared detector preamplifier circuit 1 includes a bias circuit, a signal amplification circuit, and a filtering and conditioning circuit. The acquisition circuit 2 includes an equal optical path difference detection circuit, an FPGA main control circuit, and an ADC acquisition circuit.

[0022] The bias circuit is located at the front end of the infrared detector and is used to provide a positive constant current source bias for the infrared detector to improve the responsivity of the infrared detector and make the circuit more adaptable.

[0023] The signal amplification circuit is located at the rear end of the infrared detector and is used to amplify the weak current signal in two stages to reduce the influence of offset voltage and thermal noise on the signal under test.

[0024] One end of the filtering and conditioning circuit is connected to the output of the signal amplification circuit, and the other end is connected to the ADC acquisition circuit. It is used to filter the infrared interference signal amplified by the signal amplification circuit and adjust it to match the voltage range input to the ADC acquisition circuit.

[0025] The equal optical path difference detection circuit is used to convert the input laser interference signal into a square wave signal and transmit the converted square wave signal to the FPGA main control circuit; thereby saving the resources of the lower-level processing chip and improving the data acquisition and processing efficiency.

[0026] The FPGA main control circuit receives the square wave signal transmitted from the equal optical path difference detection circuit, uses the rising and falling edges of the square wave signal as acquisition trigger signals to provide the ADC acquisition circuit, provides the driving timing for the normal operation of the ADC acquisition circuit, and transmits the data returned by the ADC acquisition circuit to the host computer.

[0027] The ADC acquisition circuit is used to convert the acquired infrared interference signals at the same optical path difference position into digital signals, and send the converted signals to the FPGA main control circuit, which then sends them to the host computer.

[0028] like Figure 2 The diagram shown is a circuit schematic of the bias circuit and signal amplification circuit according to an embodiment of the present invention. The bias circuit consists of a transistor Q1; resistors R1, R2, Rb, and Re; and a capacitor C1, wherein:

[0029] Transistor Q1 is an NPN transistor. The negative terminal B of the infrared detector is connected to the collector of transistor Q1, and the positive terminal A is connected to the bias power supply. The detection signal is output from the B terminal of the infrared detector.

[0030] Resistor Re is connected between the emitter of transistor Q1 and ground as a matching resistor for the bias power supply;

[0031] Resistor Rb is connected between the base of transistor Q1 and the bias power supply; resistors R1, R2 and capacitor C1 are connected in parallel between the base of transistor Q1 and ground; by adjusting the resistance value of resistor R1, transistor Q1 is put into amplification mode, and in amplification mode, the current of the bias power supply can be adjusted so that the infrared detector works in the best state.

[0032] In practical implementation, when transistor Q1 is operating in amplification mode, there is I c =βI bI c =I b +I e Because transistor Q1 has a very high gain, with a gain coefficient β typically greater than 100, the current I passing through the infrared detector... c ≈I e =Ve / Re=(V b -V be ) / R e The current is constant and is not affected by changes in the internal resistance Rd of the infrared detector.

[0033] like Figure 2 As shown, the signal amplification circuit consists of two operational amplifier stages. The first operational amplifier U1 is a high-bandwidth, low-noise, low-offset voltage op-amp, operating in a low-bias-current closed-loop DC mode. The feedback circuit uses a T-type resistor feedback plus differential compensation, wherein:

[0034] The signal to be detected is input from the inverting input terminal of the first-stage operational amplifier U1;

[0035] Fixed resistors R6 and R7 and adjustable resistor R8 form a T-type resistor feedback, which is connected to the output and inverting input of the first-stage operational amplifier U1 after being connected in parallel with capacitor C3.

[0036] The positive input terminal of the first-stage operational amplifier U1 is connected to a voltage divider circuit composed of resistors R4 and R5, which provides bias current to the first-stage operational amplifier U1, making the input terminal balanced and the quiescent current zero. This means that no matter how the bias power supply of the infrared detector is adjusted, it will not affect the output voltage of the first-stage operational amplifier U1. In specific implementation, the first-stage operational amplifier U1 can amplify the weak current signal into a low-noise IV signal.

[0037] The second-stage operational amplifier U2 is an operational amplifier with a high common-mode rejection ratio. It is AC coupled to the first-stage operational amplifier U1 through capacitor C4. It adopts an inverting voltage amplification form to reduce common-mode interference. The amplification factor is changed by adjusting the resistance value of resistor R10. The voltage amplification gain A = -R10 / R9 makes the amplified output signal suitable for the operating range of the ADC acquisition circuit.

[0038] In addition, such as Figure 2 As shown, after the second-stage operational amplifier U2 amplifies the signal, a third-stage operational amplifier U3 can be connected. The third-stage operational amplifier U3 serves as an emitter follower circuit to improve the stability of the preamplifier circuit.

[0039] like Figure 3 The diagram shown is a schematic diagram of the circuit structure of the filter conditioning circuit according to an embodiment of the present invention. The filter conditioning circuit includes a bandpass filter circuit and a bias adjustment circuit, wherein:

[0040] The operational amplifier U4A, resistors R13 and R14, and capacitors C5 and C6 form a second-order Butterworth high-pass filter circuit, which is used to filter out the DC component and low-frequency noise in the signal.

[0041] The operational amplifier U4B, along with resistors R15 and R16, and capacitors C7 and C8, form a second-order Butterworth low-pass filter circuit to filter out high-frequency noise in the signal.

[0042] An operational amplifier U5 is connected after the bandpass filter circuit. The operational amplifier U5 acts as an emitter follower circuit to improve the stability of the filter circuit.

[0043] The filtered signal then enters a subtractor circuit consisting of operational amplifier U6 and resistors R17-R20. The subtractor circuit outputs a stable voltage signal Ref_Source. The output signal of operational amplifier U5 is subtracted from Ref_Source to obtain a DC bias, which is used to adjust the infrared interference signal to a signal suitable for the input range of the ADC acquisition circuit.

[0044] like Figure 4 The diagram shown is a schematic diagram of the circuit structure of the equal optical path difference detection circuit according to an embodiment of the present invention. The equal optical path difference detection circuit consists of a high-speed comparator U7, a diode D1 and resistors R22-R28, forming a single-supply zero-crossing comparator circuit, which is used to convert the laser interference signal without DC component into a square wave signal.

[0045] In this system, the portion of the laser interference signal that is greater than zero is a low level, and the portion that is less than zero is a high level. The zero-crossing point is the upper and lower edges of the square wave signal, which are the points of equal optical path difference.

[0046] Furthermore, the above-described embodiments of the present invention are based on a Fourier transform infrared spectrometer using a photoconductive MCT detector, but are not limited to this embodiment and can be applied to any Fourier transform infrared spectrometer that uses a photoconductive infrared detector.

[0047] It is worth noting that the contents not described in detail in the embodiments of the present invention belong to the prior art known to those skilled in the art. For example, other constant current source circuits can be used to provide bias power to the infrared detector, and other forms of amplification circuits can be used to amplify the weak current signal; at the same time, the zero-crossing comparison circuit in the equal optical path difference detection circuit can also be replaced with other forms to obtain a square wave as the trigger acquisition signal.

[0048] In summary, the device described in the embodiments of the present invention has the following advantages:

[0049] 1. The constant current source bias circuit designed in this application enables the detector to have higher responsivity, puts the transistor into the amplification state through the adjustable resistor, and makes the bias current adjustable, which is suitable for more types of infrared detectors.

[0050] 2. The operational amplifier in the primary amplifier circuit operates in a closed-loop DC mode with low bias current, resulting in low offset voltage. Adjusting the detector bias current does not affect the output voltage of the operational amplifier. The primary amplifier circuit adopts a closed-loop feedback T-type transimpedance amplifier circuit, which can amplify the weak current signal with low noise IV signal, resulting in lower noise in the secondary amplifier circuit. This gives the preamplifier circuit advantages such as low noise, high bandwidth, high gain and strong stability.

[0051] 3. The equal optical path difference sampling circuit of this application adopts a high-speed zero-crossing comparison circuit, which provides an accurate trigger signal for the AD converter, reduces the sampling rate, increases the number of sampling bits, and can save the resources of the lower-level processing chip, reduce processing time, and improve data processing efficiency.

[0052] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims. The information disclosed in the background section is intended only to enhance the understanding of the overall background technology of the present invention and should not be construed as an admission or implication in any way that such information constitutes prior art known to those skilled in the art.

Claims

1. A weak infrared signal processing and acquisition device, characterized in that, The device comprises two parts: an infrared detector preamplifier circuit and a data acquisition circuit. The infrared detector preamplifier circuit includes a bias circuit, a signal amplification circuit, and a filtering and conditioning circuit. The data acquisition circuit includes an equal optical path difference detection circuit, an FPGA main control circuit, and an ADC data acquisition circuit, wherein: The bias circuit is located at the front end of the infrared detector and is used to provide a positive constant current source bias for the infrared detector to improve the responsivity of the infrared detector. The signal amplification circuit is located at the rear end of the infrared detector and is used to amplify the weak current signal in two stages to reduce the influence of offset voltage and thermal noise on the signal under test. One end of the filtering and conditioning circuit is connected to the output of the signal amplification circuit, and the other end is connected to the ADC acquisition circuit. It is used to filter the infrared interference signal amplified by the signal amplification circuit and adjust it to match the voltage range input to the ADC acquisition circuit. The equal optical path difference detection circuit is used to convert the input laser interference signal into a square wave signal and transmit the converted square wave signal to the FPGA main control circuit. The FPGA main control circuit receives the square wave signal transmitted from the equal optical path difference detection circuit, uses the rising and falling edges of the square wave signal as acquisition trigger signals to provide the ADC acquisition circuit, provides the driving timing for the normal operation of the ADC acquisition circuit, and transmits the data returned by the ADC acquisition circuit to the host computer. The ADC acquisition circuit is used to convert the acquired infrared interference signals at the same optical path difference position into digital signals, and send the converted signals to the FPGA main control circuit, which then sends them to the host computer.

2. The weak infrared signal processing and acquisition device according to claim 1, characterized in that, The bias circuit consists of transistor Q1; resistors R1, R2, Rb, and Re; and capacitor C1, wherein: Transistor Q1 is an NPN transistor. The negative terminal B of the infrared detector is connected to the collector of transistor Q1, and the positive terminal A is connected to the bias power supply. The detection signal is output from the B terminal of the infrared detector. Resistor Re is connected between the emitter of transistor Q1 and ground as a matching resistor for the bias power supply; Resistor Rb is connected between the base of transistor Q1 and the bias power supply; resistors R1 and R2 and capacitor C1 are connected in parallel between the base of transistor Q1 and ground. By adjusting the resistance value of resistor R1, transistor Q1 is put into amplification mode, and in amplification mode, the current of the bias power supply can be adjusted so that the infrared detector works in the best condition.

3. The weak infrared signal processing and acquisition device according to claim 1, characterized in that, The signal amplification circuit consists of two operational amplifier stages. The first operational amplifier U1 is a high-bandwidth, low-noise, low-offset voltage op-amp, operating in a low-bias-current closed-loop DC mode. The feedback circuit uses a T-type resistor feedback plus differential compensation, wherein: The signal to be detected is input from the inverting input terminal of the first-stage operational amplifier U1; Fixed resistors R6 and R7 and adjustable resistor R8 form a T-type resistor feedback, which is connected to the output and inverting input of the first-stage operational amplifier U1 after being connected in parallel with capacitor C3. The positive input terminal of the first-stage operational amplifier U1 is connected to a voltage divider circuit composed of resistors R4 and R5, which provides bias current to the first-stage operational amplifier U1, making the input terminal balanced and the static current zero. This means that no matter how the bias power supply of the infrared detector is adjusted, it will not affect the output voltage of the first-stage operational amplifier U1. The second-stage operational amplifier U2 is an operational amplifier with a high common-mode rejection ratio. It is AC coupled to the first-stage operational amplifier U1 through capacitor C4. It adopts an inverting voltage amplification form to reduce common-mode interference. The amplification factor is changed by adjusting the resistance value of resistor R10 so that the amplified output signal is suitable for the working range of the ADC acquisition circuit. After the second-stage operational amplifier U2 amplifies the signal, a third-stage operational amplifier U3 is connected. The third-stage operational amplifier U3 serves as an emitter follower circuit to improve the stability of the preamplifier circuit.

4. The weak infrared signal processing and acquisition device according to claim 1, characterized in that, The filter conditioning circuit includes a bandpass filter circuit and a bias adjustment circuit, wherein: The operational amplifier U4A, resistors R13 and R14, and capacitors C5 and C6 form a second-order Butterworth high-pass filter circuit, which is used to filter out the DC component and low-frequency noise in the signal. The operational amplifier U4B, along with resistors R15 and R16, and capacitors C7 and C8, form a second-order Butterworth low-pass filter circuit to filter out high-frequency noise in the signal. An operational amplifier U5 is connected after the bandpass filter circuit. The operational amplifier U5 acts as an emitter follower circuit to improve the stability of the filter circuit. The filtered signal then enters a subtractor circuit consisting of operational amplifier U6 and resistors R17-R20. The subtractor circuit outputs a stable voltage signal Ref_Source. The output signal of operational amplifier U5 is subtracted from Ref_Source to obtain a DC bias, which is used to adjust the infrared interference signal to a signal suitable for the input range of the ADC acquisition circuit.

5. The weak infrared signal processing and acquisition device according to claim 1, characterized in that, The equal optical path difference detection circuit consists of a high-speed comparator U7, a diode D1, and resistors R22-R28, forming a single-supply zero-crossing comparator circuit used to convert a laser interference signal without DC component into a square wave signal. In this system, the portion of the laser interference signal that is greater than zero is a low level, and the portion that is less than zero is a high level. The zero-crossing point is the upper and lower edges of the square wave signal, which are the points of equal optical path difference.

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