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Session 3232

Computer Aided Design of Internally Compensated CMOS Operational Amplifiers

M.G. Guvench * University of Southern Maine, Gorham, ME 04038

Abstract - In this paper a design procedure and successful experimental results obtained from it are being reported for implementing internally compensated operational amplifiers powered from a single power supply and with high gain-bandwidth product, good slew-rate, low output impedance and good drive levels. The procedure was developed for an in-house training course on "analog integrated circuit design" as an example of using mathematical tools (MathCad) in the design of analog integrated circuit blocks. The resulting MathCad file became a design automation tool for CMOS OpAmp Design. It is shown that all opamp specs targeted are met or exceeded by the sample opamp designed and fabricated using Fairchild Semiconductor's CS80C CMOS process with the W/L ratios predicted by this tool.

1. Introduction

In the design of electronic circuits, in particular, those falling within the classification "Analog" lack of design automation tools results in over reliance on engineering intuition and experience, and time consuming trial and error method to make the circuit "work". The more complex the circuit, and the less experience and intuition the designer has, the more the time spent becomes on trial and error runs simulating and re-simulating to find an acceptable solution. In many instances this is a justified method, because of non-linear and mathematically difficult nature of the electronic circuit design problems. However, just like in the solution of simultaneous nonlinear equations, if initial guesses are far away from the true solution, at some point the designer may face the frustrating and embarrassing situation that the trial and error method stops improving the performance and the required specs cannot be met. In order to minimize the time needed for trial and error period initial design results should be as close to the solution as possible.

In this work, design, fabrication and testing of an internally compensated CMOS operational amplifier was done complete with its reference bias current source and internal capacitor. The work was done as an example in the CMOS Analog training class taught by M.G. Guvench at Fairchild Semiconductor's Product Development Center. A MathCad file developed by the instructor was used as a design automation tool to calculate W and L parameters of all of the transistors in the circuit as well as resistors and frequency compensation capacitor in a PMOS input CMOS operational amplifier circuit.

Proceedings of the 2002 American Society for Engineering Education Annual Conference & Exposition Copyright  2002, American Society for Engineering Education

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Guvench, M. (2002, June), Computer Aided Design Of Internally Compensated Cmos Operational Amplifiers Paper presented at 2002 Annual Conference, Montreal, Canada. 10.18260/1-2--10164