As infrared light is radiated, the CMOS Readout IC (ROIC) for the microbolometer type infrared sensor detects voltage or current when the resistance value in the bolometer sensor varies. One of the serious problems in designing the ROIC is that resistances in the bolometer and replica resistor have process variation. This means that each pixel does not have the same resistance, causing serious fixed pattern noise problems in sensor operations. In this paper, differential input stage readout architecture is suggested for bias offset reduction, noise immunity and high sensing margin. In addition, using this scheme the effects of a process variation problem and various other bias heating noise problems, are reduced. In this paper, a prototype ROICs, intended for uncooled microbolometer infrared focal plane array, is designed and fabricated. The proposed architecture is demonstrated by fabrication of a prototype consisting of 32 × 32 pixels fabricated in a 0.25-μm CMOS process.