Soft-limiting control circuit for variable gain amplifiers

摘要

The input AGC and reference (REF) voltages are converted to currents and provided as differential inputs to a current amplifier. The current amplifier scales these currents proportional to absolute temperature. The translinear principle is used to realize the current amplifier and ensures linearity of the differential output currents. These currents are then converted to voltages by resistor elements. The result is applied to a simple differential pair that produces two AGC control currents that follow the hyperbolic tangent function. The two AGC control currents are equal when the AGC input is three-fourths the reference value. The overall gain response is well modeled by a second order function and is self-limiting at high gain values. <IMAGE>