195-nW 120-dB subthreshold CMOS OTA driving up to 200 pF and occupying only 4.4–10−3 mm2

An ultra-low-power high-performance three-stage subthreshold CMOS OTA is presented together with its detailed design methodology. The amplifier is realized in a 0.35-μm technology, is powered from a 1-V supply, exhibits 120-dB DC gain and is designed to drive a capacitive load up to 200 pF. Despite the allowed heavy load, it occupies only 4.4-10^-3 mm² and dissipates only 195 nW at DC, while providing 20-kHz unity gain bandwidth. Comparison with prior art shows an improvement in the figures of merit by a factor greater than 5.