Non-uniformity study on readout circuit for uncooled IR detector

Abstract

For long line uncooled infrared detectors, the non-uniformity of different detecting elements is the key parameter in measuring the circuit performance. So far there have been few research reports in this area. Most uncooled infrared detector circuits require corresponding blind detector for readout circuit design, which increases the complexity of uncooled infrared detector. In addition, the performances of these circuits need to be further improved in practical applications. In order to achieve high performance readout of the long line uncooled infrared detectors, a kind of 160 element readout circuit based on current mirror is designed in this paper. The readout circuit is composed of current mirror input part, capacitor feedback transimpedance amplifier (CTIA), and correlated double sampling (CDS) output circuit. The circuit is fabricated by using the 0.5 micron technology. The non-uniformity of circuit is obviously improved by reasonable parameter setting and current mirror circuit layout. Transconductance amplifier CTIA with capacitance negative feedback is used in the circuit. The integral capacitor consists of three capacitors whose capacitances are 10 pF, 20 pF and 20 pF respectively, thus the circuit can realize different integration capacitances, which forms different magnifications. The circuit can meet different response rates of uncooled detectors. Folded-cascode structure is adopted as the CMOS differential amplifier. The open loop gain is over 80 dB. This single-state folded-cascode construct can overcome the two-stage amplifier’s disadvantages, which easily leads to oscillations. The CDS N SF (source follow) and P SF are adopted as the circuit output, the output swing can easily be greater than 2 V. On average, the CDS N SF and P SF power consumptions are very low. So the total power consumption of 160 line circuit is lower than 100 mW. In the test, the non-uniformity of the readout circuit decreases from 10% to 1%. This result is in accordance with simulation result on non-uniformity. The other test results of total power consumption and the output amplitude also agree with simulation results. The readout circuit has good noise characteristics and the output noise is lower than 1 mV. When the readout circuit and uncooled infrared detector are connected, the infrared signal can be well read out. When the integration time is 20 μups, the device response is 0.294 mV/Ω. The overall system performance is very good. This circuit design based on current mirror has laid the technical foundation for developing readout circuit of the very large scale uncooled infrared detector in the future.