Autotracking feedback circuit and high speed A/D converter using same

Abstract

A bias circuit produces a common mode bias voltage that relies upon active, auto tracking feedback responsive to the reference voltage, such as analog ground, and to the common mode bias voltage to generate a common mode voltage for a differential amplifier. The bias circuit supports high-speed operation, and is stable with variations in temperature, manufacturing processes, and with shifts in the supply voltages. In one embodiment, the bias circuit comprises an operational amplifier and a feedback amplifier that has a common mode bias terminal coupled to the output of the operational amplifier and arranged in a feedback loop with the operational amplifier. The output of the operational amplifier is used as a common mode bias voltage for a differential amplifier. The feedback amplifier is designed to match the differential amplifier for which the common mode bias voltage is being generated, and therefore produces a common mode bias voltage that automatically produces a common mode voltage for the differential amplifier that causes proper settling. A differential amplifier and a high speed analog to digital converter utilize the autotracking, active bias circuit.

Dependencies are inferred from the claim text.