It's common knowledge that when working with single-supply op amps, implementing
simple functions in a bipolar signal environment can be difficult. Sometimes
additional op amps and other electronic components are required.
Taking that into consideration, can any advantage be attained from this mode?
The answer lies in this simple circuit (see
the figure, a). Requiring no diodes, the circuit is a high-precision
full-wave rectifier with a high-frequency limitation equaling that of the op
amps themselves. A look at the circuit's timing diagram (see
the figure, b) illustrates the principle of operation.
The first amplifier rectifies negative input levels with an inverting gain
of 2 and turns positive levels to zero. The second amp, a noninverting summing
amplifier, adds the inverted negative signal from the first amplifier to the
original input signal. The net result is the traditional waveform produced by
full-wave rectification.
In spite of the limitation on the input signal amplitude (it must be less
than VCC/2), this circuit can be useful in a variety of setups.
