The Digital modulator is having two inputs, one is channel encoded output (digital output or modulating signal) that we are multiplying it with a high-frequency carrier signal so that we can send it by the antenna.
To send a signal at a longer distance we need to translate a low-frequency digital signal into a high-frequency analog signal. That’s the reason why in a digital modulator, it converts an electrical digital signal into a high frequency modulated signal.
The basic difference between analog and digital modulation is that the modulating signal in digital communication will be digital (i.e. binary codewords). The carrier signal used by digital modulators is always a continuous sinusoidal wave of high frequency.
There are different types of digital modulation techniques like
ASK (Amplitude Shift Keying)
FSK (Frequency Shift Keying)
PSK (Phase Shift Keying)
QPSK (Quadrature Shift Keying)
MSK (Minimum Shift Keying) etc.
However, since these modulators use a continuous carrier wave, therefore they are also known as Continuous Wave(CW) Modulators.
A digital modulation method must have the following parameters.
- The bandwidth needed to transmit the signal
- Probability of symbol or bit error
- Synchronous or asynchronous method of detection
- Complexity of implementation