English: Simple diode detector used to extract the envelope of the input signal. The output signal is the voltage across the capacitor, which is alternatively charged (whenever the input signal's voltage is higher that the capacitor's voltage) and then discharged through the resistor. The resistor and capacitor values are selected to ensure their RC time constant is low enough so that the capacitor can discharge fast enough to trace the signal as it is falling, but large enough to ensure its cutoff frequency is above the input signal's maximum frequency, to prevent attenuation.