Amplifier circuit with reduced dc power related turn-on and turn-off transients

Abstract

An amplifier circuit with improved turn-on transient operation includes a differential amplifier and a selectively variable reference generator for controlling the amplifier output during circuit turn-on. The amplifier is biased by a single power supply and its differential inputs are driven by a first reference voltage from the reference generator and a single-ended input signal. Following circuit turn-on and turn-off, the first reference voltage typically charges to or discharges from, respectively, some fixed value relative to the positive power supply voltage. A comparator detects when the first reference voltage exceeds a second reference voltage and generates a control signal in response to that transition. The second reference voltage is selected to be nearly the steady-state value of the first reference voltage. The control signal (which indicates that the first reference voltage is nearing its steady-state value) is fed to a delay circuit which generates a delayed control signal. The delayed control signal tracks the first reference voltage but is delayed a sufficient amount of time to allow both the bypass capacitor of the reference generator and an input signal coupling capacitor to fully charge before switching a bypass switch on the amplifier and thereby converting the amplifier from a voltage follower to an amplifier. This allows improved turn-on transient operation to be realized, e.g., reduced “pops” and “clicks” upon circuit turn-on, while giving the user increased flexibility in selecting the sizes of the reference voltage bypass capacitor and the input signal coupling capacitor.