Browse Prior Art Database

Amplifier with Nonlinear Automatic Gain Control

IP.com Disclosure Number: IPCOM000094538D
Original Publication Date: 1965-Feb-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 2 page(s) / 25K

Publishing Venue

IBM

Related People

Schumacher, RA: AUTHOR

Abstract

This is a transistor amplifier with a delayed automatic gain control for preventing transistor saturation.

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Amplifier with Nonlinear Automatic Gain Control

This is a transistor amplifier with a delayed automatic gain control for preventing transistor saturation.

Transistors 10 and 12 are connected in cascade and provide two stages of amplification for a signal applied to input terminal 14. Feedback is applied from the emitter circuit of transistor 12 through resistor 16 to the base of transistor 10. The level of feedback through resistor 16 is controlled by the effective emitter resistance appearing at the emitter of transistor 12. This emitter resistance includes the series resistance of resistors 18 and 20. Diode switch 22 is capacitively coupled between ground and the common connection between resistors 18 and 20.

The potential applied to the midpoint of diode switch 22 is sufficient to render the switch conductive thus creating a virtual AC ground at the lower end of resistor 18 which eliminates resistor 20 from the circuit. If due to an increased level of input at terminal 14, a substantially increased signal is sensed across resistor 18, diode switch 22 becomes reverse biased and nonconductive. This has the effect of adding resistor 20 back into the emitter circuit of transistor 12. As a result, the feedback through resistor 16 increases and decreases the overall gain of the amplifier thus insuring that transistor 12 does not saturate.

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