A silicon diode analogue multiplier

The logarithmic nature of the voltage-current characteristics of silicon junction diodes is exploited to design an analogue multiplier. Four silicon junction diodes are used in conjunction with a differential operational amplifier in the multiplier circuit. The principle of operation, design considerations and techniques to compensate for temperature effects and unequal diode parameters are discussed. Methods of performing division and generation of special types of functions are outlined. Measurements on an experimental single quadrant multiplier show that an accuracy of multiplication of the order of 1% can be achieved. Long term temperature drift at the output is measured to be 2% per 10 degC change in ambient temperature. The bandwidth of the multiplier is directly dependent on the operational amplifier employed. With a Donner (Model 3400) amplifier, the bandwidth is measured to be about 200 Hz. An attractive feature of the circuit is that it lends itself for miniaturization with the advent of differential operational amplifiers in the integrated circuit form.