All four circuit variants relyon the same principle: using the analogswitch to adjust the duty-cycle ratiobetween two analog input levels, and alowpass filter (LPF) to eliminate thePWM chopping ...

Fig 1. Two analog multipliers form a VCO with quadrature outputs, while a third multiplier provides AGC to stabilize output voltages without adding distortion. Fig 2.

A decade or so ago, I designed a simple circuit that included a quad optoisolator arranged in a full-wave analog-multiplier bridge (Figure 1). It sensed and calculated watts of ac-power consumption ...