Automatic Synthesis of CMOS Operational Amplifiers: A Fuzzy Optimization Approach

ABSTRACT

In this paper, we present a method for optimizing and automating the components and transistor sizing for CMOS operational amplifiers (op-amps). The optimization approaches used for the synthesis of analog circuits are found to be very much rigid in terms of capturing human intentions. In this work, we have observed that with the use of fuzzy membership functions, human intentions for expressing wide variety of requirements, e.g., minimize power, maximize gain, etc., which are often conflicting in nature, can be captured effectively in order to formulate the objective function. For each of the performance specifications of a given topology, a membership function is assigned to measure the degree of fulfillment of the objectives and the constraints. A number of objectives are optimized simultaneously by assigning weights to each of them representing their relative importance, and then by clustering together to form the objective function that is solved by an optimization algorithm. We have considered the channel length modulation parameter for the computation of DC bias point and small signal parameters. The design results obtained from our optimization algorithm showed an excellent match with those obtained from SPICE simulation for a number of op-amp topologies.

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