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Programmable Gain Amplifier Improvement

IP.com Disclosure Number: IPCOM000063221D
Original Publication Date: 1985-Feb-01
Included in the Prior Art Database: 2005-Feb-18

Publishing Venue

IBM

Related People

Authors:
Couturier, C Galand, C Vermot-Gauchy, R [+details]

Abstract

In a previous publication [*] we have indicated how an analog-to-digital (A/D) function in a digital voice network could be improved by using a programmable gain amplifier (PGA) at the input of the A/D. The PGA operation may itself be improved to avoid a number of drawbacks when used under normal voice transmission conditions. For instance, since the amplifier gain varied slowly because it followed slow variations of the line attenuation but not fast variations of the speech input signal, and also since the gain was set at zero dB by default at the beginning of a conversation, the PGA could not adapt itself fast enough to very low input signal levels at the beginning of a conversation. Consequently, during a relatively long moment the speech signal would be chopped due to rough quantization of the coder.