Abstract
AbstractA two‐wire voice‐band automatic gain control (AGC) with echo cancellers is studied and applied to an automatic call‐transfer repeater. A four‐wire circuit model of the amplifier and its stability are discussed. Fast tracking and/or stabilizing AGC using variable‐rate control is proposed. Also, a singing protection control method in which the dominant path is selected depending on voice signal powers of the two speech paths is proposed and investigated. The amplifier gain of the inferior path is computed using the measured echo return loss (ERL) values of the echo cancellers. Furthermore, an automatic call‐transfer repeater prototype that is based on the new AGC amplifier and its characteristics is introduced.The maximum amplifier gain of the proposed methods is about 10 dB higher than that of a conventional two‐wire amplifier with a voice switch. The configuration and algorithms proposed in the paper are proven to be effective for two‐wire amplifiers.
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