Analog signal multiplier
01 January 1963
A real-time analogue multiplier uses two impedance bridges in cascade, each unbalanced to an extent dependent on one of the quantities to be multiplied. The error signal of the first bridge is used as the energisation for the second bridge hence the error signal from the second bridge is proportional to the product of the two quantities. A practical multiplier is described using a pair of shielded 4 Mc/s capacitance bridges, the voltages to the multiplied being respectively fed to variable capacitance diodes in each bridge. The error voltage of the second bridge is added to a voltage of the carrier frequency, so that the product is obtained by demodulating the combined voltages. The bandwidth is 400 kc/s and the dynamic range 40 db. The multiplier is suitable for operation on sine, pulse and triangular waves and when used as a cross-correlator to improve the signal/ noise ratio of pulse signals, is stated to detect signals having a signal/noise ratio of 1/30. Microwave operation is suggested by use of parametric diodes and distributed impedances. A theoretical treatment is given for sinusoidal signals.