1.1.1) Saturating Precision Half-Wave Rectifier Circuit (Positive Half-Wave Rectifier Circuit)
The negative half-cycle of the input does not pass to the output; it is clipped off.
If the diode polarity is reversed in Fig.7-1(a), the negative half-cycle of the input waveform will be passed to the output and the positive half-cycle will be clipped off.
The circuit can rectify signals with peak values down to a few millivolts, unlike conventional diodes.
The high open-loop gain of the op-amp automatically adjusts the voltage drive to the diode D1 so that the rectified output peak is the same as the input (Figure 8-25b).
As Vin starts increasing in the positive direction, the also starts increasing positively until diode D1 is forward biased.
When D1 is forward biased, it closes a feedback loop and the op-amp works as a voltage follower.
Therefore, the output voltage Vo follows the input voltage Vin during the positive half-cycle, as shown in Figure8-25(b).
When Vin starts increasing in the negative direction, also increases negatively until it is equal to the negative saturation voltage ( -VEE).
This reverse biases diode D1 and opens the feedback loop.
Therefore, during the negative half-cycle of the input signal, Vo is 0 V.
The op-amp must be a high-speed op-amp since it alternates between open-loop and closed-loop operation.
A318, HA2500, and LM310 are typical examples of high-speed op-amps.
Figure 8-25 (a) Positive small-signal half-wave rectifier circuit. (b) its input and output waveforms.