Digital modulation involves modulating an analog carrier signal with a discrete digital signal. The main digital modulation techniques are based on keying, including phase-shift keying (PSK) which uses a finite number of phases, frequency-shift keying (FSK) which uses a finite number of frequencies, and amplitude-shift keying (ASK) which uses a finite number of amplitudes. FSK transmits digital data by changing the discrete frequencies of a carrier wave, ASK represents digital data as variations in the amplitude of a carrier wave, and PSK conveys data by modulating the phase of a carrier wave.

1. Digital Modulation

2. In digital modulation, an analog carrier signal
is modulated by a discrete signal.
Digital modulation methods can be
considered as digital-to-analog conversion,
and the corresponding demodulation or
detection as analog-to-digital conversion.

3. • The most fundamental digital modulation
techniques are based on keying:
PSK (phase-shift keying): a finite number of
phases are used.
FSK (frequency-shift keying): a finite number of
frequencies are used.
ASK (amplitude-shift keying): a finite number of
amplitudes are used.

4. FSK
• Frequency-shift keying (FSK) is a frequency
modulation scheme in which digital
information is transmitted through discrete
frequency changes of a carrier wave.

5. Fig: binary FSK

6. ASK
• Amplitude-shift keying (ASK) is a form of
amplitude modulation that represents digital
data as variations in the amplitude of a carrier
wave.

7. PSK
• Phase-shift keying (PSK) is a digital
modulation scheme that conveys data by
changing, or modulating, the phase of a
reference signal (the carrier wave).