TDLAS hardware phase-locked circuit

Abstract

The utility model relates to the technical field of tunable semiconductor laser absorption spectrums, in particular to a TDLAS (tunable diode laser absorption spectroscopy) hardware phase-locked circuit, which comprises a singlechip, a tunable semiconductor laser, a band-pass filter, a phase-locked amplification chip and a low-pass filter. A DAC of the single-chip microcomputer outputs a scanning signal modulated by superposing 40kHz sine waves to drive the tunable semiconductor laser, a light beam of the tunable semiconductor laser passes through the long-optical-path absorption cell and then is converted into an electric signal through the photodiode, and the electric signal output by the photodiode passes through the band-pass filter, the lock-in amplification chip and the low-pass filter and then is transmitted to the single-chip microcomputer. And a second harmonic signal is output to the ADC of the single-chip microcomputer. According to the utility model, a traditional DDS (signal generator) is omitted, so that the cost is effectively reduced; and when different modulation amplitude outputs are carried out, compared with a traditional DDS, the device is more sensitive, independent modulation of single gas in multi-component gas can be achieved, the sensitivity is higher, and production and application are more convenient.

Description

Technical Field

[0001] The utility model relates to the technical field of tunable semiconductor laser absorption spectroscopy, in particular to a TDLAS hardware phase-locked circuit. Background Art

[0002] Tunable semiconductor laser absorption spectroscopy (TDLAS) utilizes the narrow linewidth and wavelength of tunable semiconductor lasers that change with the injected current to measure a single or several closely spaced absorption lines of molecules that are difficult to distinguish. Due to its high selectivity, high resolution, and lack of interference from other gases, it has become a commonly used atmospheric trace gas monitoring technology.

[0003] Currently, the main applications for TDLAS include wavelength modulation (WM) technology and direct absorption technology (DA). The main differences between the two are high precision (WM is more applicable) and high range (DA is more applicable). For wavelength modulation technology (WM), the traditional hardware phase-locked circuit uses a dedicated DDS (signal generator) chip to output high-frequency signals, but its price is generally high. At the same time, the flexibility of using DDS is poor. In a short period of time, such as 25 to 50 ms, it cannot quickly respond to output different modulation amplitudes (involving the process of initialization-writing to registers-communicating with the chip and waiting for output, which takes a certain amount of time). Therefore, when modulating and scanning multiple gas components, DDS generally uses unified modulation parameters. Under unified modulation parameters, there will be the problem of premature saturation of individual gases, affecting the signal-to-noise ratio of single gas measurements.

[0004] Therefore, for wavelength modulation technology (WM), a hardware phase-locked circuit solution that can not only reduce costs but also achieve a better signal-to-noise ratio for a single gas when monitoring multiple gas components and ensure measurement accuracy is a technical problem that needs to be solved. Utility Model Content

[0005] The purpose of the present invention is to provide a TDLAS hardware phase-locked circuit to address the deficiencies of the above-mentioned prior art, so as to achieve the purpose of reducing costs and obtaining a better signal-to-noise ratio for a single gas, thereby ensuring measurement accuracy.

[0006] To achieve the above-mentioned purpose, the present utility model adopts the following technical solution: a TDLAS hardware phase-locked circuit, comprising a single-chip microcomputer;

[0007] The single chip microcomputer drives the tunable semiconductor laser;

[0008] The tunable semiconductor laser is matched with a photodiode;

[0009] The photodiode is connected to a transconductance circuit, the transconductance circuit is sequentially connected to a bandpass filter, a phase-locked amplifier chip and a low-pass filter, and the low-pass filter is connected to a single-chip microcomputer.

[0010] Furthermore, the single chip microcomputer is connected to a follower circuit, the follower circuit is connected to a constant current circuit, and the constant current circuit is connected to a tunable semiconductor laser.

[0011] Furthermore, the follower circuit is connected to a DAC pin of the single chip microcomputer.

[0012] Furthermore, the laser light emitted by the tunable semiconductor laser is absorbed by the gas to be measured and then converted into an electrical signal through a photodiode.

[0013] Furthermore, the laser light emitted by the tunable semiconductor laser is emitted into the long optical path gas absorption cell, is absorbed by the gas to be measured in the long optical path gas absorption cell, and then emitted and converted into an electrical signal by a photodiode.

[0014] Furthermore, the low-pass filter is connected to the ADC pin of the single-chip microcomputer.

[0015] Furthermore, it also includes a reference signal circuit of the phase-locked amplifier chip.

[0016] Furthermore, one side of the reference signal circuit is connected to the IO pin of the single chip microcomputer, and the other side is connected to the reference signal pin of the phase-locked amplifier chip.

[0017] Beneficial effects of the utility model:

[0018] 1. High flexibility and segmented independent modulation: Using the MCU's hardware DAC for high-frequency waveform output allows for more flexible segmented modulation while ensuring the quality of the output waveform. For multiple components with different absorption intensities, different modulation amplitudes can be output to achieve a better signal-to-noise ratio for a single gas, thus avoiding the problem of premature saturation of individual gases under unified modulation parameters.

[0019] 2. High cost performance: The traditional hardware phase-locked circuit uses a dedicated DDS chip for high-frequency signal output, but its price is generally high. After using this solution to improve it, the price of a single-board PCB can be reduced by about one-third. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a circuit diagram of the utility model circuit;

[0021] Figure 2 This is a schematic diagram of the system framework of the utility model;

[0022] Figure 3This is a schematic diagram of different modulation amplitude outputs of the DAC of the utility model single-chip microcomputer. DETAILED DESCRIPTION

[0023] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field fall within the scope of protection of the present invention.

[0024] Embodiments of the present utility model:

[0025] like Figure 1 As shown, in this embodiment, U1 (CPU) is a single-chip microcomputer, and the DAC pin of U1 outputs a sawtooth scanning signal superimposed with a 40kHz sine wave modulation through R1, and passes through the follower circuit of U2A to enhance the driving capability, and drives the tunable semiconductor laser through the constant current circuit of U3A. The tunable semiconductor laser LED1 emits light, and after the light beam passes through the long optical path gas absorption cell, the photodiode D1 receives the laser signal, which is converted into a voltage signal through the first-level transconductance circuit U3B, and then passes through a high-pass filter (C1 R4), a phase-locked amplifier chip (U4, the reference signal is 2F in the figure, generated by the IO pin of the single-chip microcomputer), and a low-pass filter (R5C2), and then output to the single-chip microcomputer for ADC acquisition.

[0026] The principle of this utility model is:

[0027] In the present invention, the traditional DDS (signal generator) is replaced by a single chip microcomputer.

[0028] like Figure 2 As shown, the DAC (digital / analog converter) of the single-chip microcomputer outputs a scanning signal superimposed with a 40kHz (1F) sine wave modulation, and drives a tunable semiconductor laser through the scanning signal. After the tunable semiconductor laser beam passes through the long optical path gas absorption cell, it is converted into an electrical signal by a photodiode. The long optical path gas absorption cell is an existing one, and its structure and principle are not described in detail here.

[0029] The electrical signal output by the photodiode passes through a bandpass filter, a lock-in amplifier chip, and a low-pass filter, and then outputs a second harmonic signal to the ADC (analog / digital converter) of the microcontroller.

[0030] The output signal of the microcontroller also includes a double frequency signal (2F) synchronized with the above-mentioned modulated sine wave, which is output using ordinary IO. This signal is used to provide a switching reference to the phase-locked amplifier. Among them, the 1F and 2F signals must be output synchronously to ensure the stable output of the second harmonic.

[0031] The utility model adopts a single chip microcomputer to replace a traditional dedicated DDS chip for high frequency signal output, which can reduce the price of single board PCB by about one third, making it more economical.

[0032] In addition, compared with the traditional DDS chip, the present invention has higher flexibility and can perform segmented independent modulation; Figure 3 As shown, when changing the modulation amplitude, the traditional DDS chip involves the process of initialization-writing to the register-communicating with the chip and waiting for the output, which takes a certain amount of time. However, with the utility model, only the output register needs to be changed, and there is no need to communicate with the chip or wait for the chip to respond. Under the premise of ensuring the quality of the output waveform, segmented modulation can be performed more flexibly (such as using a sine wave amplitude in the first half of the sawtooth scanning signal and another sine wave amplitude in the second half of the sawtooth scanning signal). For multiple components with different absorption intensities, different modulation amplitudes can be output to obtain a better signal-to-noise ratio for a single gas, thereby avoiding the problem of premature saturation of individual gases under unified modulation parameters.

[0033] For example, when monitoring two-component gases of ethane and methane, a mid-infrared tunable semiconductor laser is used with a central wavelength of 3.345um. By adjusting the scanning current amplitude, the laser emission wavelength is controlled at 3344.4nm and 3345.8nm, while covering the absorption peak positions of ethane and methane, thus achieving more accurate measurement of a single component in a multi-component gas.

Claims

1. A TDLAS hardware phase-locked circuit, characterized in that: Including microcontroller; The single chip microcomputer drives the tunable semiconductor laser; The tunable semiconductor laser is matched with a photodiode; The photodiode is connected to a transconductance circuit, the transconductance circuit is sequentially connected to a bandpass filter, a phase-locked amplifier chip and a low-pass filter, and the low-pass filter is connected to a single-chip microcomputer.

2. A TDLAS hardware phase-locked circuit according to claim 1, characterized in that: The single chip microcomputer is connected to the follower circuit, the follower circuit is connected to the constant current circuit, and the constant current circuit is connected to the tunable semiconductor laser.

3. A TDLAS hardware phase-locked circuit according to claim 2, characterized in that: The follower circuit is connected to the DAC pin of the single chip microcomputer.

4. A TDLAS hardware phase-locked circuit according to claim 1, characterized in that: The laser light emitted by the tunable semiconductor laser is absorbed by the gas to be measured and then converted into an electrical signal through a photodiode.

5. A TDLAS hardware phase-locked circuit according to claim 4, characterized in that: The laser light emitted by the tunable semiconductor laser is emitted into the long optical path gas absorption cell, is absorbed by the gas to be measured in the long optical path gas absorption cell, and then emitted out and converted into an electrical signal through a photodiode.

6. A TDLAS hardware phase-locked circuit according to claim 1, characterized in that: The low-pass filter is connected to the ADC pin of the single-chip microcomputer.

7. A TDLAS hardware phase-locked circuit according to claim 1, characterized in that: It also includes a reference signal circuit for a phase-locked amplifier chip.

8. A TDLAS hardware phase-locked circuit according to claim 7, characterized in that: One side of the reference signal circuit is connected to the IO pin of the single chip microcomputer, and the other side is connected to the reference signal pin of the phase-locked amplifier chip.

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