Research On Detection Technology Of The Weak Signals In The Passive Infrared Spectroscopy

Passive dynamic FTIR spectrometer can be used for the spectral analysis ofenvironmental radiation, IR remote sensing technology is also increasingly applied to thetarget compounds exploration and gas identifying in an open environment. The infrared signaldetection plays an important role in spectrometer. IR signal conditioning circuit has a directimpact on the detecting accuracy of spectrometer.For I-V conversion, signal processing, low noise amplification and high speed A/Dconversion of the weak current signal at the output of photoelectric detector, a set of lowsignal conditioning circuit (including the pre-amplifying circuit and the amplifying circuit)and A/D conversion circuit based on HgCdTe photoconductive IR detector is designed in thispaper against the background of passive interference atmospheric IR spectral detectiontechnology. It can be concluded from the theoretical analysis which are compared withMultisim software simulation results and validated results of welded plate testing that theweak signals can be amplified efficiently. This design has a high signal to noise ratio (SNR)and good stability, which verify its correctness and feasibility. It also provides usefulexperience for future work.This paper mainly introduced the weak signal conditioning circuit of medium and farinfrared wave detector in the passive dynamic interference atmospheric remote sensing IRspectrometer, including:1) The project background and significance, the development situation both in China andabroad are reviewed by this paper. The detecting methods, principles overviews and the majorresearch content are especially focused on.2) The energy and index distribution of Infrared radiation which reaches to thephotoconductive detector is deeply researched for later design in the spectrum telemetrysystem. Based on the design concept of circuit, it requires high SNR, high sensitivity, high gain, small temperature drift and strong anti-jamming capability. Using a filtered powersupply, and a high-speed, low-noise and high-precision operational amplifier, a circuit isdesigned through a reasonable choice of components and layout. After receiving andtransferring interference light to the weak current of the output signal of detector, thedifferential circuit, phase compensation circuit and secondary amplifier circuit are designed.Using the theory of standard circuit for the equivalent noisy model, the circuit superpositionmethod can be used to calculate the total noise of output voltage and SNR. Finally noisesuppression method is proposed from the engineering point.3) Compared the simulation results by Multisim software and the welded plateexperimental data with the theoretical results, the influential factors of IR detecting circuitmeasurement accuracy have been analyzed.