Abstract :
Two instruments, which provide analogue multiplication in all four quadrants, are described. The principle used in the first multiplier is that of varying the saturation point of a ferro-magnetic circuit in proportion to one of the inputs, so as to control the mark/space ratio of a chopper, which then modulates the other input. The second multiplier uses the principle of modulating the phase of one square wave with respect to another similar wave in proportion to one of the input signals. Zero modulation corresponds to a phase difference of ¿/2. This wave then chopper modulates the other input signal, and the resultant output is combined with the original square wave in a synchronous demodulator. After suitable filtering in both cases, the desired product is obtained. The accuracy is better than ±1 % of full-scale output.
