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Automatic Level Control with Mean Square Response

IP.com Disclosure Number: IPCOM000090327D
Original Publication Date: 1969-Apr-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 30K

Publishing Venue

IBM

Related People

Hellwarth, GA: AUTHOR [+2]

Abstract

This device has a variable gain amplifier and a feedback circuit. Automatic control of the average of the square of the output signal is realized. Input signal IS enters variable gain amplifier VGA whose output is connected to peak clipper PC. The latter prevents the output signals OS from passing predetermined values +E and -E. The feedback circuit is connected at the output of PC. It comprises full-wave rectifier R providing a signal representative of the absolute value of OS, square-law network SQ providing a signal representative of the square of OS, and transconductance amplifier TA providing a current I which is proportional to the square of OS.

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Automatic Level Control with Mean Square Response

This device has a variable gain amplifier and a feedback circuit. Automatic control of the average of the square of the output signal is realized. Input signal IS enters variable gain amplifier VGA whose output is connected to peak clipper PC. The latter prevents the output signals OS from passing predetermined values +E and -E. The feedback circuit is connected at the output of PC. It comprises full-wave rectifier R providing a signal representative of the absolute value of OS, square-law network SQ providing a signal representative of the square of OS, and transconductance amplifier TA providing a current I which is proportional to the square of OS.

A first branch B1 of output circuit B of TA is connected to a constant current source CS so that, in operation, current I1 in this branch is constant. A second branch B2 of circuit B is connected to capacitor C which is connected to ground. Current I2 flowing through branch B2 is used to charge capacitor C. Voltage V at the P terminal of C is applied to gain control terminal GS of VGA.

Source CS which discharges capacitor C determines both the mean-square output amplitude and the gain recovery rate. Since the average current flowing into the integrating capacitor is zero, the constant discharge current I1 is equalled on the average by charge current I.

A sudden increase in the input signal provides a rapid gain reduction due to amplifier overload denoted by the clipp...