Variable gain amplifier (VGA) circuits and methods implemented in such
circuits are disclosed. An example VGA circuit includes a differential
transistor pair for receiving a differential input signal. The
differential transistor pair, in operation, conducts a substantially
constant current over a linear operating range of the variable gain
amplifier circuit. The VGA circuit also includes a current source that is
coupled with the differential transistor pair. The current source, in
operation, provides the substantially constant current to the
differential transistor pair. The VGA circuit further includes a variable
resistance circuit coupled with the differential transistor pair. In
operation, a resistance of the variable resistance circuit is adjusted
such that a gain of the variable gain amplifier circuit is adjusted.
Further, in operation, the VGA circuit produces a differential output
signal, the differential output signal being an amplified version of the
differential input signal.