A high-performance monolithic multiplier using active feedback

Since its conception in 1967, the linearized transconductance multiplier (LTM) has rapidly gained acceptance as the preferred approach to the realization of monolithic analog multipliers, and its simplicity has commended it for use in low-cost modular designs. Accuracies of these units have been limited to about 0.5 to 2 percent, and drift and noise performance have generally been worse than that possible using the dominant alternative technique of pulse-width-height modulation. This paper shows that when careful attention is given to all the sources of error it is possible to attain a five-fold improvement in accuracy and corresponding reductions in the drift and noise levels. Odd-order nonlinearities can be reduced to negligible magnitudes by the use of active feedback, by substituting the usual resistive-bridge feedback path by an amplifier identical to that used as the input stages.