Voltage-controlled amplifiers (VCAs) find applications in AM modulation/demodulation, signal multiplication/division, and automatic gain control, to name a few. In the literature, there is a plethora of circuits that implement the voltage-controlled gain function. In a modulator, the main concern is the control signal delay or phase shift; one would not like to see a delay in the voltage gain after a step change occurs in the control signal (Fig. 4.1b). This article describes a VCA designed around an opamp and an enhancement MOS transistor. The primary goal is to achieve a voltage gain that varies with the control voltage as linearly as possible while providing wideband operation.