Automatic gain control by differential pair current splitting
Igor M. Filanovsky, V. A. PISKAREV · International Journal of Electronics · 1987
A bipolar differential pair used as a current splitter is applied in the amplifier automatic gain control (AGC) circuit. The output voltage of the intermediate amplifier supplies current (via a resistor) to the point of emitter coupling of the differential pair. The current splitting is controlled by the base voltages of the pair. One collector output of this pair is used to provide additional voltage controlled feedback in the intermediate amplifier, another output provides the voltage controlled signal transfer to the output amplifier. The proposed method is applied to low-voltage power supply bandpass amplifier circuit. The gain control of 40 dB with − 47 dB total harmonic distortions (THD) in the total gain control range was achieved with a power supply of 3-75 V.