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Power Amplifier (Buffer) With Low Output Impedance and Current Measurement Capability

IP.com Disclosure Number: IPCOM000040603D
Original Publication Date: 1987-Dec-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 2 page(s) / 47K

Publishing Venue

IBM

Related People

Hansen, AC: AUTHOR

Abstract

This article describes an amplifier which exhibits a low output impedance without inducing thermal runaway. The amplifier permits accurate output current measurement over several decades. Active current limiting and tristateable load disconnect are also achievable. (Image Omitted) The power amplifier 10 shown in Fig. 1 is represented by a five port device. The input and bias control ports draw negligible current. The current entering the amplifier is monitored with sense resistors (RS). The current monitoring circuit 12 separates the components of the amplifier output IO and bias currents IB. The bias current is compared with a reference and active feedback is employed to maintain this value. The actual configuration of the power amplifier is dependent on the particular circuit requirements.

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Power Amplifier (Buffer) With Low Output Impedance and Current Measurement Capability

This article describes an amplifier which exhibits a low output impedance without inducing thermal runaway. The amplifier permits accurate output current measurement over several decades. Active current limiting and tristateable load disconnect are also achievable.

(Image Omitted)

The power amplifier 10 shown in Fig. 1 is represented by a five port device. The input and bias control ports draw negligible current. The current entering the amplifier is monitored with sense resistors (RS). The current monitoring circuit 12 separates the components of the amplifier output IO and bias currents IB. The bias current is compared with a reference and active feedback is employed to maintain this value. The actual configuration of the power amplifier is dependent on the particular circuit requirements. Accurate current measurements dictate that minimal current enter the input and bias control ports.

FET inputs should be provided in these applications. Cascading of emitter followers is required in high current applications.

Extremely low output impedance will require biasing between upper and lower transistors in the amplifier. This will not affect output current measurement accuracy, but will generate an offset in the bias current measurement. This offset must be accounted for when setting the bias reference voltage. Fig. 2 represents a typical amplifier configuration. Operational amplifie...