VARIABLE-GAIN AMPLIFIER CONTROLLED BY AN ANALOG SIGNAL AND HAVING A LARGE DYNAMIC RANGE

摘要

A variable-gain amplifier including a ladder attenuator to which the input signal is applied. The ladder nodes develop progressively attenuated (reduced level) signals corresponding to the input signal. Controllable-transconductance (gm) stages are connected respectively to the ladder nodes, and a composite of their outputs is directed to a fixed-gain output amplifier. The transconductances of the gm stages are controlled by an interpolator circuit which steers a control current to each of the gm stages in sequence in response to an analog control signal as it is varied between minimum and maximum attenuation values. The control current activates each gm stage in sequence, raising the transconductance of each from effectively zero to maximum and then back to zero, in an overlapping fashion, so as to smoothly lower the overall gain of the variable-gain amplifier as the control signal is swept through its control range.