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Audio Automatic Gain Control Amplifier With Nonvarying Time Constant

IP.com Disclosure Number: IPCOM000077231D
Original Publication Date: 1972-Jun-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Hess, WJ: AUTHOR

Abstract

This automatic gain control (AGC) amplifier 10 reduces the overload time and increases the signal detection capability of an active sonar system, by making the feedback time constant insensitive to target amplitude. This is accomplished by the inclusion of the logarithmic amplifier 15 in the error or feedback loop.

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Audio Automatic Gain Control Amplifier With Nonvarying Time Constant

This automatic gain control (AGC) amplifier 10 reduces the overload time and increases the signal detection capability of an active sonar system, by making the feedback time constant insensitive to target amplitude. This is accomplished by the inclusion of the logarithmic amplifier 15 in the error or feedback loop.

More specifically, amplifier 10 has a voltage-controlled gain stage 11. Stage 11 has a linear voltage versus log gain characteristic. The output of stage 11 is connected to AC amplifier 12, which in turn feeds into a feedback loop that contains the series connected precision full-wave rectifier 13, error detector 14, log amplifier 15, low-pass filter 16 and DC amplifier 17.

The linear voltage versus log gain controlled gain characteristic maintains a constant steady-state look gain for at least 86 DB of input dynamic range. The AC signal Eo after being rectified and filtered by stages 13 and 14 is compared with a fixed DC reference voltage V ref to develop the error voltage v. The steady-state loop gain, which is proportional to the feedback loop time constant is determined by the change of output voltage Eo caused by the change of control voltage v. Since the output Eo is essentially constant for any input within the operating range, the steady-state gain for small changes is essentially constant. In the absence of amplifier 15 in the feedback loop, however, if the background noise level is one-tenth, e.g. 20DB of the maximum signal level, the time constant decreases to one-tenth its value presented at the average output, i.e. noise level when a signal Ein is received. A corresponding increase of the...