US Patent 7417500 Control of an adjustable gain amplifier

A method of controlling an adjustable gain of an amplifier is disclosed. The method includes setting an output of a replica amplifier to be equivalent to a precision reference with a control loop, summing an adjustable offset voltage into the control loop, adjusting the adjustable offset voltage until an error offset voltage of the control loop is nulled, and controlling the adjustable gain of the amplifier with an output of the control loop. An apparatus for controlling an adjustable gain of an amplifier is also disclosed. The apparatus includes a control loop for setting the adjustable gain. The control loop includes an adjustable gain replica amplifier. A switch receives an output of the replica amplifier and a precision reference. An error amplifier receives outputs from the switch and generates a control voltage. The control voltage controls an adjustable gain of the replica amplifier and the adjustable gain of the amplifier.