active rectifier without diodes

The active rectifier proposed here is based on the property of an oper- ational amplifier that its output cannot become negative if its power supply is asymmetrical. We have used an RCA type CA 3130 opamp which is eminently suitable, because it can cope with input voltages down to 0 V, and has a CMOS output stage that can also work down to 0 V. With a supply voltage of 15 V, the maximum input level is about 1.2 Vrms. The frequency range, for not more than 1 dB change in output, extends from DC to just over 25 kHz. Negative half cycles at the input of the opamp are inverted and amplified by a factor R2/R1. Positive half cycles are also inverted, but, as stated, the out- put of the opamp cannot become negative, and it therefore remains at 0 V. The positive half cycles are also applied to the output of the opamp via a resistive divider, R1-R2-R3-P2. The result of all this is that only positive half cycles are present at the output, just as if full-wave rectification had 7-66 active r...