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High speed precision rectifier
This circuit uses two OP-27s to form a high speed precision rectifier. For positive inputs, the 2N4393 FET (which acts as a diode in this circuit) conducts and D1 is biased off. The OP-27 op amps act as a follower with output-to-input feedback. For negative inputs, D1 conducts and the FET is biased off. The first op amp acts as a follower and the second op amp serves as a precision inverter. In this mode, matching of R1 and R2 is critical to gain accuracy. This circuit provides full-wave rectification for inputs of up to +/-10v and up to 20kHz in frequency. To assure frequency stability, be sure to decouple the power supply inputs and minimize any stray capacitive loading.