# Peak Detector Circuit

Posted on Feb 7, 2014

A Peak Detector is any circuit that functions to detect the peak voltage of an incoming waveform. Basically the circuit is used as an Amplitude Modulation [AM] detector, Pulse Amplitude Modulation [PAM] detector or Envelope detector. The particular circuit covered in this topic is the diode detector, in its basic form. The most basic form of a pea

k detector uses a single diode to limit current flow in only one direction and a capacitor which charges up to the highest voltage applied to it [the peak voltage]. A resistor is than added to provide a discharge path for the capacitor. Of course the circuit is using the minimum number of parts. However the peak detected voltage will always be one diode drop below the actual incoming voltage peak. The capacitor may leak, and not stored, or hold the maximum voltage applied to it, and the discharge time of the capacitor needs to occur before the next incoming peak. That is the RC time constant needs to be selected to match the incoming signal, so the capacitor will charge through the diode [Dr x C] and discharge through the resistor [R x C]. However your not likely to see this circuit used, other than in a lab experiment, but you should still find it in text books. The waveforms to the right are just an example of an amplitude modulated signal, which is detected by the diode, and than Envelope detected by the capacitor. The next circuit is an upgrade, of the same approach, using a few more components of course. This next circuit is an example of a peak detector used as a pulse amplitude demodulator. The same waveforms to the right still apply, although PAM is normally just a single polarity. Diode CR1 performs the same function as before and allows capacitor C1 to charge while a positive pulse is applied to the circuit. When...

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