1.2) Nonsaturating Precision Half-Wave Rectifier Circuit
The output signal is taken from the junction between R2 and D2.
When the input signal is positive, diode D1 is forward-biased and all the feedback current flows through D1; the output of the circuit is zero because D2 is reverse-biased (Figure 8-2b).
When the input signal goes negative, D1 is reverse-biased, and because D2 is forward-biased, the feedback current flows through both D2 and R2 in series.
A signal then appears at the output across R2.
As soon as the input level goes negative, the output of the operational amplifier jumps to the positive level required to cause D2 to conduct.
This effectively eliminates any diode drop from the output signal.
Once diode D2 begins to conduct, the circuit behaves as a conventional inverting amplifier.
If R1=R2, the closed-loop gain is unity.
Thus, the output signal is nearly an exact half-wave-rectified version of the input without the undesirable effects due to the diode drop.
For this reason, this type of circuit is then referred to as a precision half-wave rectifier.
On the other hand, if desired, the negative-going half-cycle at the output could be achieved merely by reversing the direction of both diodes