Introduction
Demodulation is the act of extracting the original information bearing signal from a modulated carrier wave. A demodulator is an electronic circuit that is used to recover the information content from the modulated carrier wave.In other words we can say that the demodulation is just the opposition of a modulation process. An AM signal is a modulated signal that is high – frequency carrier amplitude varied with low frequency audio amplitude for transmission. To recover the audio signal in receiver, it is necessary to extract the audio signal from an AM signal.
There are several ways of demodulation depending on how parameters of the base-band signal are transmitted such as amplitude, Frequency or Phase.An AM signal encodes the information onto the carrier wave by varying its amplitude indirect sympathy with analog signal to be sent. There are two different methods used to demodulation of AM signals.
Envelope Detector: - The envelope detector is a very simple method of demodulation. It consists of a rectifier and a low pass filter. The rectifier may be in the form of a single diode, and the filter is usually an R-C low pass type. This is the general used circuit.
Product Detector: - The product detector multiplies the incoming signal by the signal of a local oscillator with the same frequency and phase as the carrier of the incoming signal. After filtering the incoming signal the original audio signal will result. This type of detector is used to demodulating the Balanced Amplitude Modulation.
This is by far the simplest form of AM demodulator or detector, requiring just a semiconductor or diode along with a capacitor and resistance to remove the high frequency components. The main element of AM demodulation is to create the base-band signal. This can be achieved by using a simple diode and rectify the signal. The filtering by R-C low pass filter removes the all unwanted high frequency elements from the input signal.
