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 0.35µm 2-poly 4-metal CMOS process for a 320×240 microbolometer array with a pixel size of 35μm × 35μm. The noise equivalent temperature difference (NETD) was estimated to be 47mK, with a power consumption of 390nW for a pixel-level ADC.