Gain enhancement and input parasitic capacitance reduction of single-stage OTAs by using differential voltage combiners

A new technique to enhance single-stage operational transconductance amplifiers (OTAs) is presented. Enhanced DC gain and reduced input parasitic capacitances are achieved by employing two input fully-differential voltage combiners, i.e. a combination of transistors in common-drain and common-source configurations operating as a preamplifier stage. Simulation results show that the input capacitance can be as small as 195 fF (corresponding to a 46 % reduction) while achieving a GBW of 1982 MHz (@ CL = 1 pF) with a PM of about 60°. The complete amplifier dissipates only 1.78 mW corresponding to a figure-ofmerit (FoM) of 1115 MHz·pF/mW.