Abstract: An amplifier, including a pair of emitter coupled non-complementary transistors operated at constant emitter, base and collector potentials, provides a bidirectional output current proportional to an AC signal to be rectified. The output current is applied to a common base connection of a pair of complementary emitter-coupled base-coupled transistors having a common emitter connection coupled via a linearizing feedback resistor to the base electrode of one of the amplifier transistors and via a load to a source of reference potential.

Abstract: A pair of voltage followers, having offsets which differ by a fraction of the threshold voltage of a diode, are coupled to respective sources of signal and load voltage to provide unequally offset ouput voltages. An amplifier, coupled to the voltage followers, provides an output current when the difference of the signal and load voltages is of a given sense and magnitude, the output current being substantially zero otherwise.

Abstract: A resistance-capacitance filter smoothes the control voltage of an audio signal expander. An analog gate couples the greater, in a given sense, of the smoothed control voltage and a further voltage to the control terminal of a variable gain device in the audio signal path, the further voltage being equal to the filter input voltage less a constant equal to Vbe. A time constant modifier circuit reduces the filter time constant when the filter input voltage differs in either sense from the smoothed control voltage by a fraction, less than unity, of Vbe. The resultant, relatively "narrow" dead zones of the adaptive filter enable operation of the expander with relatively low signal voltage levels thereby enabling a corresponding reduction in supply voltage requirements and providing further advantages such as reduced power dissipation, reduced heat build-up and improved reliability.