The design of input stage amplifier becomes more and more difficult as the expansion of format arrays and reduction of
pixel size. A design method of low-offset amplifier based on 0.18-μm process used in small-size pixel is analyzed in
order to decrease the dark signal of extended wavelength InGaAs infrared focal plane arrays (IRFPA). Based on an
example of a cascode operational amplifier (op-amp), the relationship between input offset voltage and size of each
transistor is discussed through theoretical analysis and Monte Carlo simulation. The results indicate that input transistors
and load transistors have great influence on the input offset voltage while common-gate transistors are negligible.
Furthermore, the offset voltage begins to increase slightly when the width and length of transistors decrease along with
the diminution of pixel size, and raises rapidly when the size is smaller than a proximate threshold value. The offset
voltage of preamplifiers with differential architecture and single-shared architecture in small pitch pixel are studied.
After optimization under same conditions, simulation results show that single-shared architecture has smaller offset
voltage than differential architecture.