Development of an analog and mixed-signal read-out circuit for long-wavelength infrared focal-plane arrays

Abstract

We designed, fabricated and tested two prototypes of read-out circuit arquitectures using a 0.18um standard CMOS technology aiming the fabrication of focal-plane arrays (FPAs) for applications to infrared imaging. One small capacitive transimpedance amplifier (CTIA) was designed for high-resolution analog FPAs, as well as a novel mixed-signal architecture which has several advantages over the analog design, such as a wider dynamic range, a native digital output, a longer integration time and a faster system development. The read-out circuits were electrically tested at room temperature and liquid-nitrogen temperature (77 K) and, later, were connected to a photovoltaic quantum-well infrared photodetector cooled at 10K to check the properties of the whole system. The CTIA performed as expected. The mixed-signal circuit appeared to be able to measure currents from pA to nA with a good linearity and low noise. The calculated resolution was about 50,000 e-/bit, and integration times from milliseconds to a few seconds could be reached without any saturation. The results confirm that such circuits can be used for the design of state-of-the-art intersubband FPAs with very few modifications.