Quite often we have to send digital data through analog transmission media such as a telephone network. In such situations it is essential to convert digital data to analog signal.
Basic approach is shown in Figure below. This conversion is accomplished with the help of special devices such as modem (modulator-demodulator) that converts digital data to analog signal and vice versa.
ASK, FSK, and PSK with Neat Diagram
Digital to Analog conversion
Digital data needs to be carried on an analog signal.
A carrier signal (frequency fc) performs the function of transporting the digital data in an analog waveform.
Amplitude Shift Keying (ASK)
ASK is implemented by changing the amplitude of a carrier signal to reflect amplitude levels in the digital signal.
For example: a digital “1” could not affect the signal, whereas a digital “0” would, by making it zero.
Frequency Shift Keying(FSK)
The two binary values are represented by two different frequencies
Phase Shift Keying (PSK)
The phase of carrier signal is shifted to represent the data.
In PSK , the phase is varied to represent binary 1 or 0.