Simple diode detector:- Explanation:- This is essentially just a half wave rectifier which charges a capacitor to a voltage nearly to the peak voltage of the incoming AM waveform s(t). When the input wave's amplitude increases, the capacitor voltage is increased via the rectifying diode. When the input's amplitude falls, the capacitor voltage is reduced by being discharged by a ‘bleed’ resistor, R. The main advantage of this form of AM Demodulator is that it is very simple and cheap! Just one diode, one capacitor, and one resistor. That's why it is used so often.
Explanation:- The circuit diagram for a practical diode is as shown in Figure, as the direction of the diode has been reversed, the negative envelope will be demodulated. Due to this a negative AGC voltage will be developed. R1 and R2 provide a series dc path. R1 - C2 is the low pass filter which is used to remove the RF ripple that is still present in the detected output. The capacitor C2 is a coupling capacitor which prevents the diode dc output from reaching the volume control potentiometer R4. Hence across R4 we get the demodulated signal with a zero dc shift. This signal is then applied to the AF amplifier. The R3-C3 combination forms a low pass filter. It is designed to remove the AF component from the demodulator output. This filter will allow only dc part to pass through, which is used as AGC voltage. This AGC voltage is then applied to the RF and IF amplifiers to control their gain automatically. Such a practical diode detector circuit is in the domestic radio receivers. The dc AGC voltage produced at the detector output is proportional to the signal strength. Stronger Am signal higher is the dc AGC voltage.