Digital Modulation And its techniques ?? II Part 2 II ASK II PSK II PSK II FSK II QAM II ADC

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• Digital Modulation Schemes
– Amplitude Shift Keying (ASK)
– Frequency Shift Keying (FSK)
– Phase Shift Keying (PSK)
– Quadrature Amplitude Modulation (QAM)
Digital Modulation
• Digital modulation is the process of modulation where an analog sinusoidal signal is modulated by the digital data.
• One or two parameters (Amplitude, Frequency and Phase) of the sinusoidal waveforms are modified with respect to the digital data.
• Amplitude Shift Keying (ASK)
– Amplitude of the sinusoidal is varied to carry Information.
Frequency Shift Keying (FSK)
– Frequency of the sinusoidal is varied to carry Information.
• Phase Shift Keying (PSK)
– Phase of the sinusoidal is varied to carry Information.
• Quadrature Amplitude Modulation (QAM)
– Amplitude and phase of the sinusoidal is varied to carry Information.

Amplitude Shift Keying (ASK)
• In ASK, the amplitude of the carrier is changed in response to information and all else is kept
fixed.
• Bit ‘1’ is transmitted by the carrier of one particular amplitude.
• Bit ‘0’ is transmitted by the carrier of another amplitude.
• All the other parameters of the carriers are kept constant which include frequency and phase.
• On Off Keying (OOK) is a special case of ASK where one of th amplitudes is ‘Zero’.

Frequency Shift Keying (FSK)
• In FSK the frequency of the carrier signal is varied to carry information.
• Different binary signals are represented by different frequency sinusoids.
• All other parameters including amplitude and phase are kept constant.
• The simplest Frequency Shift Keying (FSK) is Binary FSK.
• In BFSK, a binary ‘1’ is represented by one frequency while a binary ‘0’ is represented by another frequency.

Phase Shift Keying (PSK)

• Phase Shift Keying (PSK) is the type of modulation in which the phase of the carrier sinusoid is
varied according to the digital data.
• PSK uses finite number of phases to represent single bits or unique combination of bits.
• Depending upon the number of bits represented by a phase, PSK has different variants known as M-PSK.
• Binary Phase Shift Keying (BPSK)
– Two phase levels represent ‘1’
and ‘0’.
• Quadrature Phase Shift Keying
(QPSK) or 4-PSK
– Four phase levels represent 4 different bit combinations or symbols.
• 8-PSK
– Eight phase levels represent 8 different bit combinations or symbols
• In BPSK, a binary ‘1’ is represented by a phase of zero degrees while a binary ‘0’ is
represented by 180 degrees. All other parameters of the carrier sinusoid are kept constant.
Quadrature Phase Shift Keying (QPSK)
In QPSK, four different symbols are represented by four distinct phases.

8-Phase Shift Keying (8-PSK)
• In 8-PSK, eight different binary symbols are represented by 8 distinct phases.
Quadrature Amplitude Modulation(QAM)

• In Quadrature Amplitude Modulation (QAM) both amplitude and phase are varied simultaneously to carry information.
Find Answers to

• What is Grey Coding?
• Spectral Comparison of ASK, FSK, PSK and QAM?

Edition McGraw Hill Education, ISBN: 978—0-07-337385-0v
[1] B.P. Lathi, Modern Digital and Analog Communication Systems, 3
rd Edition,
[1] Bernard Sklar, Digital Communications- Fundamentals and Applications, 2
nd

Edition.
[2] http://www.soundonsound.com/sos/jan06/articles/qa0106_2.htm
[3] Louis E. Frenzel Jr., Principles of Electronic Communication Systems, 4
th

Edition McGraw Hill Education, ISBN: 978—0-07-337385-0[1] Bernard Sklar, Digital Communications- Fundamentals and Applications, 2
nd

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