High-Voltage High Slew-Rate MOSFET Op-Amp Design 2005 Engineering Design Expo University of Idaho Erik J. Mentze Jennifer E. Phillips April 29, 2005 Project Sponsor: Apex Microtechnology Advisors: Dave Cox, Herbert Hess

Overview → Project Description → Design Methodology → Theory of Operation → Implementation and Results → Conclusions and Future Work

Project Description Develop a high-voltage (+/- 200 V) high slew-rate (1000 V/us) MOSFET op-amp.

Apex currently offers op-amps that operate at 400 volt differentials with slew-rates of 1000 V/μs. These products are open-frame type designs, utilizing discrete surface-mount components. Our goal is to develop an amplifier design that matches these performance specifications, while being well suited to IC implementation. Project Description

Design Methodology Output Voltage Limitations Power Limitation (P=IV) High-Voltage High Slew-Rate

General Amplifier Topologies Find topology candidates Throw out those that are obviously deficient Analytically compare the “finalists” to make the best choice Hardware Implementation Find components that meet our design requirements Adapt chosen topology to meet physical requirements Simulate Implementation Attempt to Implement Design

Significant Increase in Circuit Complexity! Theoretical Considerations Modern Amplifier Research Focus: Reducing Size of Frequency Compensation Capacitor(s) Two Techniques to Improve Slew-Rate: 1. Reduce Capacitances 2. Increase Current

Active Frequency Compensation Three-Stage Dual-Path Amplifier - reduce capacitance - increase current drive

Theory of Operation The active nature of the feedback allows us to model the frequency and phase response of the amplifier as an Active RC Filter and fit it to response function we choose.

A good choice for maximum bandwidth and good phase margin is a third-order Butterworth response:

Implementation

Devices Found TO92 Package: Zetex ZVN0545A Zetex ZVP0545A Surface Mount: Zetex ZVP0545G

TO92 Specifications N-ChannelP-Channel Drain-Source Voltage 450 V-450 V Continuous Drain Current 90mA-45 mA Pulsed Drain Current600 mA400 mA Power Dissipation750 mW Gate-Source Voltage+/- 20 V

Implementation

Uncompensated Operational Results DC Gain: 110dB Unity Gain Freq: 100MHz

Compensated Operational Results DC Gain: 110dB Unity Gain Freq: 10MHz Phase Margin: 35 o

Slew-Rate Results Rail-to-Rail Operation Slew-Rate: 2000 V/us!

Implementation

Test Setup

Conclusions We have shown that active feedback techniques can be successfully implemented as a means of achieving extremely high-slew rate op-amp designs. DC Gain: 110dB Unity Gain Freq: 10MHz Slew-Rate: 2000 V/us Further testing of the prototype will be conducted by Apex in Tucson, Arizona Implementation in an integrated circuit form. Future Work

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