Design Automation of Fully-Differential Folded Cascode OTA Using Nested Iterations

Analog amplifiers are indispensable in any analog/mixed-signal system. The design of an operational transconductance amplifier (OTA) to meet a set of specifications is a non-trivial task that requires analog design expertise and time consuming simulations. In this paper, we present a systematic and automated design flow for the most popular integrated circuit OTA architecture, namely, the folded cascode OTA. The design procedure is customized for using the OTA in a fully-differential switched capacitor amplifier application. The presented design flow uses the gm/ID methodology and is automated using MATLAB. The OTA transistor sizing is computed using a nested iterative procedure. The design procedure takes into account the effect of several circuit parameters that have no closed form solutions, without invoking a simulation engine inside the loop. A complete design example is illustrated and verified using Cadence Spectre simulator.