Current-mode absolute value circuits for wideband performance

Absolute value circuits or precision full-wave rectifiers (PFWRs) exhibit significant zero-crossing distortion at high frequencies. This is due to an inherent problem as the circuit changes from noninverting to inverting gain as the input signal changes polarity. In this paper two entirely different topology PFWR BJT circuits are explored. In the first one a differential current switching technique is used so that rapid switching with minimum transients can be achieved. The switch adopted is essentially a fully-switched differential pair, commonly referred to here as a nonsaturating current-mode switch. In the second circuit topology an emitter-coupled common-collector PFWR with NPN quasi-Darlingtons is designed and tested. The second circuit has the advantage that switching transients are reduced