Types Of ASK Demodulation
There are mainly two types of Demodulation which is performed namely envelope detection and coherent detection technique:
- Envelope detection
- Coherent detection
Envelope detection
Envelop detection is a relatively simpler method as compared to coherent detection which is used for demodulating Amplitude Shift Keying (ASK) signals. It primarily focuses on extracting the envelope of the modulated signal to recover the original digital data.
The steps involved in this technique is as follows
- The modulated ASK signal, which contains the carrier signal and the digital data, is received by the demodulator. This is called receiving of signal.
- The received signal is then passed through a diode. The diode rectifies the signal, allowing only the positive portion of the waveform (the envelope) to pass through it. This process is called Diode Rectification.
- Following the rectification process, a low-pass filter is applied to the rectified signal. This filter helps remove or discard the high-frequency carrier signal, leaving the varying amplitude that represents the original digital data. This process is called Low-Pass Filtering of the modulated signal.
- Once the signal has been filtered by passing it through the LPF, a threshold detection mechanism is used to interpret the amplitude changes. Comparing the amplitudes to a predefined threshold helps to determine the transmitted digital data. If the amplitude is above the threshold, it might be interpreted as one bit ‘1’, and if it’s below the threshold, it might be interpreted as the other bit ‘0’. This is called Threshold Detection.
- The message signal is recovered from the modulated signal.
ASK Demodulator
Coherent detection
This is another method which is used for demodulation of ASK signal. It involves phase synchronization with the carrier wave.
The steps involved in this technique is as follows
- The received signal is mixed with a local oscillator, aligning its phase and frequency with the original carrier signal. This process is called Reception.
- Filtering isolates the part of the mixed signal that corresponds to the data signal.
- The demodulator sets an amplitude threshold to distinguish between the ‘1’ and ‘0’ states.
- The amplitude of the received signal is compared against the threshold to determine the transmitted data.
In this way the original message signal is recovered.
ASK Coherent detection demodulation
Amplitude Shift Keying
In digital communication, different modulation techniques are used to transmit data or message to receiver over a communication channel . One such technique is Amplitude Shift Keying (ASK). It is a modulation technique that alters the amplitude of a carrier signal to transmit the information over channel. It is a modulation scheme having wide range of application in real world which includes radio, television, and digital data transmission.