In order to obtain the scene image, the infrared imaging system firstly decomposes the scene in space, and then sequentially converts the scene temperature of these unit spaces into corresponding time-series video signals. The basic task of signal processing in infrared imaging is to form a video signal corresponding to the degree of the scene. If you want to measure the temperature, you must also mark the temperature of each part of the scene according to the video signal corresponding to each unit of the scene.
Jiangwai imaging system and common TV camera system have many things in common in signal processing, such as amplification, filtering, TV signal synthesis and so on.
According to the fact that the signal output by the infrared detector is very weak and contains noise, the design requirements for the preamplifier are: low noise, high gain, low output impedance, large dynamic range, and good linearity characteristics. Also, carefully shielded to eliminate interfering signals. When the impedance of the detector and the preamplifier do not match, the emitter output circuit can be used to overcome the problem. When the signal amplitude variation range is very wide and it is impossible to use a gain switch, a logarithmic gain preamplifier can be used to ensure high gain for weak signals and low gain for strong signals. In order to ensure the low noise figure of the system, the minimum gain of the preamplifier should be 10, so as to ensure that the noise generated by the subsequent amplifiers is negligible. In most system applications, a preamplifier with an electrical gain of 0100 is most suitable. For most tube preamplifiers, when the voltage output exceeds a few volts, it begins to saturate, so for this type of preamplifier, the maximum output signal is often 1V. Therefore, the dynamic range of the preamplifier should not be too large, which is limited by the noise level of the detector at the input and the maximum allowable output signal.
After the design of the preamplifier is completed, it should be verified by experiments whether the parameters meet the requirements of the indicators. If some indicators do not meet the requirements, repeated modifications should be made until the preamplifier is in the noise figure, gain, bandwidth, stability and Impedance matching and other aspects meet the index requirements.