Sizing CMOS Amplifiers by PSO and MOL to Improve DC Operating Point Conditions

The sizes of the metal-oxide-semiconductor (MOS) transistors in an operational amplifier must guarantee strong direct current operating point (DCOP) conditions. This paper shows the usefulness of two population-based optimization algorithms to size transistors, namely-particle swarm optimization (PSO) and many optimizing liaisons (MOL). Both optimization algorithms link the circuit simulator SPICE to measure electrical characteristics. However, SPICE provides an output-file indicating that a transistor is in strong inversion but the DCOP can be in the limit, and it can switch to a different condition. In this manner, we highlight the application of PSO and MOL to size operational transconductance amplifiers (OTAs), which DCOP conditions are improved by the introduction of a procedure that handles constraints to ensure that the transistors are in the appropriate DCOP. The Miller and RFC-OTA are the cases of study, and their sizing is performed using UMC 180 nm CMOS technology. In both OTAs, the objective function is the maximization of the gain-bandwidth product under the main constraint of guaranteeing DCOPs to improve two figures of merit and to provide robustness to Monte Carlo simulations and PVT variations.