High-Performance Audio Amplifier with AGC Control and Signal Clipping for Portable Military Radio
Henk C. Nauta, Ernst H. Nordholt · 1986
An automatic-gain controlled audio amplifier and clipping amplifier, destinated for driving a transmitter in a portable military radio, is presented. Over the military temperature range (-40°C - +85°C), the clipping level and the level where the AGC starts controlling the gain, drift by amounts no larger than 0.3dB and 0.09dB, respectively. This is the result of a novel system control loop, which largely eliminates offset and offset-drift in both the DC-coupled amplifiers whilst realising a large amount of transimpedance gain (3MEG Ω). Over the AGC control range (40dB) the output level only varies 0.2dB. The complete circuit, which also contains a microphone preamplifier and a digitally controlled power amplifier, has been integrated on an EXAR M-100 semicustom chip.