Subthreshold DC-gain enhancement by exploiting small size effects of MOSFETs

A pseudo-cascode split-transistor technique is proposed for DC-gain enhancement of amplifiers in the subthreshold by exploiting the small size effects of metal-oxide semiconductor field effect transistors (MOSFETs) including the reverse short-channel effect and the inverse narrow-width effect. It requires no body-biasing and occupies a small area. A compact 114 μm² two-stage amplifier with pseudo-cascode compensation for in-pixel amplification in vision sensors has been designed using the proposed technique. A total of 10 samples of split-transistors and amplifiers fabricated in an UMC 0.18 μm standard CMOS process were measured. More than half of the tested split-transistors show considerable DC-gain enhancement over a wide range of bias currents and nine amplifiers have increased DC gains larger than 85 dB at about 4 nA power consumption.