Analogue multiplier using p--njunction capacitance

One input voltage of the multiplier acts upon the dynamic capacitance of a p-njunction. The other input voltage acts upon the frequency of a square-wave signal. During half a period of the square-wave signal, the current in the RC circuit decays exponentially to nearly zero. The detected current is proportional to the product of the input voltages. The limitations of the multiplier are the one-quadrant multiplier and the limited maximum frequency response.