Patent ID: 8139791
Filing Date: 2012-03-20
Classification: H03F

Abstract:
1. A ground-referenced headphone amplifier comprising: a first audio amplifier operable to receive a first audio input signal, the first audio amplifier including a standby mode trigger control input; a sense comparator circuit operable to sample the first audio input signal, the sense comparator circuit also operable to supply an indicator of a presence of audio input signal levels below a specified level; and a sense logic circuit operable to receive the indicator from the sense comparator circuit, the sense logic circuit in electrical connection with the standby mode trigger control input of the first audio amplifier; wherein the sense logic circuit is operable to monitor a duration of the indicator and, upon detecting the duration exceeding a predetermined amount of time, to provide a control signal to the first amplifier to enter a standby mode in which the first amplifier draws less current; and wherein the sense comparator circuit comprises first and second stages, the first stage configured to provide a first gain to reduce a random offset to less than a first offset value, the second stage configured to provide a second gain that, when combined with the first gain, provides a positive offset that is greater than the first offset value.