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OPTIMIZATION OF PERFORMANCE AND SIZING OF TWO STAGE AND FOLDED CASCODE OP AMPS

by BHANGAONKAR, AVINASH SUDHAKAR

Abstract (Summary)
The design of an opamp is a fairly complex task in itself. This thesis deals with the optimization of two-stage and folded cascode opamps. The optimization problems are considered to be non-linear constrained optimization problems; the constraints being non-linear. The cost function and constraints are formulated using the level 1 MOSFET model. The Matlab function ‘fmincon’ has been used for the actual optimization process. A GUI is provided for the user so that the specifications can be readily changed. The GUI designed in Visual Basic accepts the specifications and then writes the constraints file based on that. It then proceeds to optimize the design in Matlab. In case of two-stage opamp, there is an option to choose the set of functions whose weight can be varied in the cost function. The cost functions are, DC gain, size, power and gain bandwidth. The optimization process creates an array of points for the design and allows the user to select any point for simulation with PSpice. For a folded cascode operational amplifier optimization, the initial guess is very important, because the problem is highly non-linear. Taking this into consideration, the cost function is kept fixed as the size and the initial guesses are varied over a wide range, which can also be changed by the user. The plots in this case are the parametrical functions of the opamp, viz. DC gain vs. size vs. power, and gain bandwidth vs. phase margin vs. slew rate. Again, the user can select any point from the plot to simulate in SPICE. The software writes a SPICE netlist for the specified point and also launches PSpice, so that the design can be readily verified. This tool has been developed for analog designers who can appreciate the tradeoffs in the design procedure. A variety of optimal points is generated so that the designer can decide for herself/himself the specifications that can be compromised. An Excel file is written so that the details of the design elements are accessible to the user.
Bibliographical Information:

Advisor:

School:University of Cincinnati

School Location:USA - Ohio

Source Type:Master's Thesis

Keywords:opamp optimization analog circuit two stage and folded cascode

ISBN:

Date of Publication:01/01/2002

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