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Precession Half Wave Rectifier

One of the non-linear behaviors that are sometimes required in analog circuits is rectification. Rectification is a process of separating the positive and negative portions of a waveform from each other and selecting from them what part of the signal to retain. In the case of half-wave rectification, we can choose to keep one polarity while discarding the other.

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The circuit above accepts an incoming waveform and as usual with op amps, inverts it. However, only the positive-going portions of the output waveform, which correspond to the negative-going portions of the input signal, actually reach the output. The direct feedback diode shunts any negative-going output back to the “-” input directly, preventing it from being reproduced. The slight voltage drop across the diode itself is blocked from the output by the second diode.

The second diode allows positive-going output voltage to reach the output. Furthermore, since the output voltage is taken from beyond the output diode itself, the op amp will necessarily compensate for any non-linear characteristics of the diode itself. As a result, the output voltage is a true and accurate (but inverted) reproduction of the negative portions of the input signal. Thus, this circuit operates as a precision half-wave rectifier. If Rf is equal to Rin as is the usual case, the output voltage will have the same amplitude as the input voltage.

 

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