Pixel-Level ADC with Two-Step Integration for 2-D Microbolometer IRFPA

Abstract

A readout circuit incorporating a pixel-level analog-to-digital converter (ADC) is studied for 2-dimensional microbolometer infrared focal plane arrays (IRFPAs). The integration time and signal-to-noise ratio (SNR) is improved using the current-mode bias and MSB skimming. The proposed pixel-level ADC is a two-step configuration, so its power consumption is very low. The readout circuit was designed using a 0.35 mu m 2-poly 4-metal CMOS process for a 320 x 240 microbolometer array with a pixel size of 35 mu m x 35 mu m. The noise equivalent temperature difference (NETD) was estimated to be 47 mK, with a power consumption of 390 nW for a pixel-level ADC.