Feedback stabilized four-quadrant analog multiplier

A technique utilizing an ideal controlled current fork as a fundamental building block is evolved to generate the product of two variables. A particularly useful implementation of the technique, making use of the exact exponential characteristics of the emitter-base junction of the bipolar transistor to realize a controlled current fork, is demonstrated. It is shown that a mismatch of transistor pairs and a mismatch of resistance values give rise to certain predictable errors for which quantitative expressions are derived in order to determine acceptable tolerances. Measurements on a particular design are given to support the theoretical derivations, and the operation of the multiplier as a squarer, independent of transistor-pair mismatch, is demonstrated.