| With increasingly widespread applications of infrared imaging system in both military and civil fields, designing such systems with high sensitivity is becoming an essential task. For a selected infrared detector, the noise analysis of infrared detector and hardware circuit reveals the dominant factors affecting the system sensitivity are: 1) bias voltage noise of the detector; 2) noise introduced by signal conditioning and acquisition circuit; 3) system power noise. This thesis aims at improving infrared imaging sensitivity through designing low noise drive circuit and low noise, high efficient system power supply.Firstly, in low noise drive circuit design, this thesis gives an extensive analysis on the noise model of drive circuit’s amplifier. Output noise is calculated through derived noise model. Low noise circuit design scheme is propose and an ultra-low noise drive circuit is accomplished. The design comprises of two major parts: designing a low noise bias voltage circuit to decrease the infrared detector’s fixed pattern noise and shot noise; designing a low noise analog signal conditioning circuit and full differential signal acquisition circuit to reduce the noise introduced in the conditioning, transmission and collection of the infrared analog signal. The circuit schematic design and placement and routing in multi-layer PCB is finally given.Secondly, in respect of system power supply design, we give an in-depth study in the operation principles and design fundamental rules of various power supply design techniques, providing theoretical basis for the design task next step. Multiple requirements of system power supply are considered: high transient response, high efficiency, high current requirements for digital circuits such as FPGA; low noise, high accuracy requirements for analog circuit. Emphasizing on low noise and high efficiency requirements, we propose a multi-stage multi-channel power supply design framework, based on which schematic design of power modules and placement and routing in multi-layer PCB are carried out.The test results demonstrates that our proposed drive circuit’s performance reach a minimum noise of 6.12μV(RMS value, 1Hz~100KHz)in the bias voltage circuit, which proves to be an effective design. The overall efficiency of the proposed system power supply design is 75.5% along with a minimum noise of 13.6mV in digital power output. An even lower noise level of less than 2mV is also achieved in analog output. Thus, this low noise and high efficiency performance indicates the effectiveness of our system power supply design. The finally measured NETD of the circuit is 7.319 mK, which provides an effective guarantee for the longwave cooled infrared imaging system to achieve high sensitivity while giving further verification on the performance of our proposed drive circuit and power supply. |
