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Amplitude Limiting Amplifier

IP.com Disclosure Number: IPCOM000095328D
Original Publication Date: 1965-Nov-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 31K

Publishing Venue

IBM

Related People

Skarshinski, L: AUTHOR

Abstract

The circuit is a variable gain amplifier. There is increased gain for small amplitude input signals and reduced gain for higher strength signals. Conversely, it acts to limit the amplitude of higher strength signals.

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Amplitude Limiting Amplifier

The circuit is a variable gain amplifier. There is increased gain for small amplitude input signals and reduced gain for higher strength signals. Conversely, it acts to limit the amplitude of higher strength signals.

The line input appearing on the input transformer is amplified by a DC coupled amplifier consisting of T1... T4. A feedback loop consisting of R1, R2, C1, and the transformer secondary provides DC stabilization. The second feedback loop consisting of D1, D2 and C2 provides nonlinear amplification and symmetrical clipping around the zero volt level of input signal. In the second feedback loop, C2 acts only to block DC feedback. D1 and D2 function as variable resistance devices. These have a high resistance at low voltage signal levels and a lower resistance at higher signal levels. Thus, high gain at low signal levels is realized. As the signal increases, the resistances of D1 and D2 drop to reduce the amplifier gain.

Using silicon diodes and transistors, the output is substantially constant for inputs ranging from 20 m. v. to 20 v. The circuit also achieves symmetrical clipping of sinusoidal inputs, independent of the power supply. An input impedance of about 15K is achieved with output levels of 0. 5 volts. The output level can be increased by adding additional diodes in series with those shown.

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