Design of folded cascode opamp using Potential Distribution Method

Abstract

In this work, design of CMOS opamps using Potential Distribution Method (PDM) is discussed. PDM is a newly proposed device sizing technique for analog circuits based on voltage distribution at different nodes. This technique is free from complex mathematical expressions governing the devices and the circuit. Instead of relying on analytical design approach, PDM directly utilizes the simulator as a device sizing tool to meet the target specifications. This is achieved by first designing the circuit with moderate performance by logically or uniformly allocating node voltages and then modifying these node potentials to meet the target specifications. PDM is also technology independent and can be applied to both, long and short channel devices. A fully differential folded cascode opamp is then designed using PDM. Dependency of response of the opamp on different node voltages is discussed. It is shown how PDM can be employed to fine tune the opamp's response to meet the specifications and the simulation results are presented.