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High Gain DC Preamplifier

IP.com Disclosure Number: IPCOM000095398D
Original Publication Date: 1965-Dec-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 21K

Publishing Venue

IBM

Related People

Sordello, FJ: AUTHOR

Abstract

This circuit is a high-gain power driver preamplifier. It provides power to a bridge network to drive a servo-actuator. The circuit provides high differential gain, high common mode rejection and temperature tracking for both differential and common mode levels.

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High Gain DC Preamplifier

This circuit is a high-gain power driver preamplifier. It provides power to a bridge network to drive a servo-actuator. The circuit provides high differential gain, high common mode rejection and temperature tracking for both differential and common mode levels.

The circuit employs transistors T1, T2, T3. The emitters of T1 T2 and T3 are tied together. The inputs from a DC wideband source are applied at points X and Y to the transistor bases. Both differential and common mode signals are applied to the bases of T1 and T2. Only common mode signals appear at the base of T3.

These common mode signals and the temperature dependent base-to- emitter voltage drop of T3 are applied to the emitters of T1 and T2. Common mode signals are thus effectively cancelled. Thus only the differential signals have any effect on the switching action of T1 and T2.

For differential level temperature variation tracking the base-to-emitter drops of T1 and T2 track each other. For common mode level temperature variation tracking the base-to-emitter drop of T3 tracks that of T1 and T2. Since T3 is in the emitter-follower configuration and since the emitters and bases of T1 and T2 are referenced to the same common mode signal, power supply variations do not effect the switching action of T1 and T2.

This circuit feeds the input signal forward to cancel common mode signals, rather than feeding the amplifier signal back. This arrangement leaves the differential gain of...