Editing Envelope detector (section)

== Diode detector ==
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| footer            = Simple diode detector. An input voltage (the green [[Amplitude modulation|AM]] signal) is first [[Half-wave rectification|rectified]] by the [[diode]]. The output voltage (red) ripples just below the input's upper envelope by charging and discharging the [[capacitor]].
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A simple form of envelope detector used in [[Detector (radio)|detectors]] for early [[Radio|radios]] is the '''diode detector'''. Its output approximates a voltage-shifted version of the input's upper envelope.

Between the circuit's input and output is a [[diode]] that performs [[half-wave rectification]], allowing substantial current flow only when the input voltage is around a [[Diode forward voltage drop|diode drop]] higher than the output terminal.

The output is connected to a [[capacitor]] of value <math>C</math> and [[resistor]] of value <math>R</math> in parallel to [[ground (electricity)|ground]]. The capacitor is charged as the input voltage approaches its positive peaks. At other times, the capacitor is gradually discharged through the [[resistor]]. The resistor and capacitor form a 1st-order [[low pass filter]], which attenuates higher frequencies at a rate of -6 dB per octave above its [[cutoff frequency]] of <math>\tfrac{1}{2 \pi R C}</math>. The filter's [[RC time constant]] <math>(\tau {=} R C)</math> must be small enough to track quickly-falling envelope slopes and "top up" the envelope's voltage every peak to prevent ''negative peak clipping''.<ref name=":0">{{Cite web |last=Lesurf |first=Jim |date=2000-05-18 |title=The Envelope Detector |url=https://www.winlab.rutgers.edu/~crose/322_html/envelope_detector.html |url-status=live |archive-url=https://web.archive.org/web/20230326153521/https://www.winlab.rutgers.edu/~crose/322_html/envelope_detector.html |archive-date=2023-03-26 |access-date=2024-06-09 |website=www.winlab.rutgers.edu}}</ref>

=== AM demodulation ===
Envelope detectors can be used to [[demodulate]] an [[amplitude modulated]] (AM) signal. Such a device is often used to demodulate AM [[radio signal]]s because the envelope of the modulated signal is equivalent to the [[baseband]] signal. To sufficiently attenuate the frequency of the [[carrier wave]] frequency <math>f_\text{carrier}</math>, the cutoff frequency of the low-pass filter should be well-below the carrier wave's frequency. To avoid negative peak clipping, the original signal that is modulated is usually limited to a maximum frequency <math>f_\text{max}</math> to limit the maximum rate of fall of the AM signal. To minimize distortions from both ripple and negative peak clipping, the following inequality should be observed:<ref name=":0" />

<math display="block"> \frac{1}{f_\text{carrier}} \ll \tau \ll \frac{1}{f_\text{max}} \; .</math>

Next, to filter out the DC component, the output could pass through a simple high-pass filter, such as a DC-blocking capacitor.