This document discusses different types of digital modulation techniques. It begins by defining modulation as the process of modifying characteristics of a high frequency carrier signal using a low frequency information signal. The key types of digital modulation covered are: 1) Amplitude Shift Keying (ASK) which modifies the amplitude of the carrier based on the binary input signal. 2) Frequency Shift Keying (FSK) which shifts the frequency of the carrier between two frequencies (mark and space) depending on the binary input. 3) Phase Shift Keying (PSK) which shifts the phase of the carrier by 180 degrees depending on the binary input state for Binary PSK, and by multiple phase shifts for techniques like Quadrature P

1. Digital modulation
techniques
Submitted By - KM Sakshi Verma
Roll no.-1705918
Section-CS12

2. In this presentation, we will study about
• What modulation is ?
• Categories of modulation (Analog and Digital)
• Types of Modulation (Analog and Digital)

3. 1. Modulation
• Modulation is a process of suppressing low frequency information
signal on a high frequency carrier signal.
OR
Modulation is a process of modifying the any of the characteristics
(amplitude, frequency, phase) of
high frequency carrier in accordance with low frequency information
signal.

4. • Remember, for modulation require two signals, high frequency
carrier and low frequency
information signal (also called modulation signal).
• The resultant wave achieved known as “modulated signal”.
i.e. information (modulating signal) + carrier = modulated signal.
• Why there is need of modulation? • Is there any substitute of
modulation?

6. 2. Categories of modulation
Remember that while considering categories of modulation
• In either type of modulation (analog or digital), carrier is of analog
format. • Why not digital carrier? • The only difference between both
categories is type of information (modulating) signal.
i.e. analog modulation = analog information signal
digital modulation = digital information signal • Also remember in
modulated wave, the resultant change is in the respective
characteristics of high frequency carrier.

7. 3. Types of Modulation
3.1 Digital modulation
• Basically we will study three main types of digital modulation. a) Amplitude
Shift Keying (ASK) b) Frequency Shift Keying (FSK) c) Phase Shift Keying
(PSK)
a) Amplitude Shift Keying (ASK)
• The simplest digital modulation technique. • a binary information signal
directly modulates amplitude of an analog carrier. • Similar to amplitude
modulation except there are two output amplitude possible only. •
Mathematically can be expressed as

8. VASK(t) = [ 1 + Vm(t)] [ (Ac/2) cos(ωct) ]
Where • VASK(t) = Amplitude Shift Keying Modulated wave • Vm(t) = Amplitude
of binary modulating (information) signal • (Ac/2) = Amplitude of un-modulated
high frequency carrier • ωc = 2πfc = un-modulated high frequency carrier.
a) Amplitude Shift Keying (ASK)
Vm (t) = logic 1 = +1V Vm (t) = logic 0 = -1V
VASK(t) = [ 1 + Vm(t)] [ (Ac/2) cos(ωct) ] VASK(t) = [ 1 + Vm(t)] [ (Ac/2) cos(ωct)]
= [ 1 +1] [ (Ac/2) cos(ωct) ] = [ 1 - 1] [ (Ac/2) cos(ωct) ]
= [2] [ (Ac/2) cos(ωct) ] = [0] [ (Ac/2) cos(ωct) ]
= [Ac cos(ωct) ] =0

9. Output waveform

10. Conclusion:
• As information signal is of binary format, only two voltage levels occur
at input (either +1V or -1V) • As a result, we get only two voltage levels
at output (either [Ac cos(ωct) ] or OV) • because of these two output
voltage levels, the carrier is either in “ON” or “OFF” state. • that’s the
reason why ASK is also known as “ON-OFF Keying (OOK)”

11. b) Frequency Shift Keying (FSK)
• Simple and low performance type of digital modulation. • a binary information
signal directly modulates frequency of an analog carrier.
• Mathematically can be expressed as
VFSK(t) = Vc cos[ 2π (fc + Vm(t)Δf)t ]
Where • VFSK(t) = Frequency Shift Keying Modulated wave • fc = Analog carrier
central frequency • Vc = peak analog carrier amplitude • Vm(t) = binary input
(modulating) signal • Δf = peak change (shift) in the analog carrier frequency

12. Vm(t) = logic 1 = +1V Vm(t) = logic 1 = -1V
VFSK(t) = Vc cos[ 2π (fc + Vm(t)Δf)t ] VFSK(t) = Vc cos[ 2π (fc + Vm(t)Δf)t ]
= Vc cos[ 2π (fc + 1.Δf)t ] = Vc cos[ 2π (fc - 1.Δf)t ]
= Vc cos[ 2π (fc + Δf)t ] = Vc cos[ 2π (fc - Δf)t ]

13. We observed that in FSK
• carrier wave continuously shifted by an amount specified as Δf.
• when logic 1 input is applied, the carrier wave modulated itself to a
frequency known as “mark frequency (fm)”.
• when logic 0 input is applied, the carrier wave modulated itself to a
frequency known as “space frequency (fc)”.
• the overall spectrum of FSK will be observed

14. Output waveform

15. c) Phase Shift Keying (PSK)
• PSK is another form of angle modulated (later define in upcoming slides) constant
amplitude digital modulation. • PSK is an M-ary digital modulation scheme
• a binary information signal directly modulates phase of an analog carrier.
• Simplest form is “Binary phase shift keying” (BPSK)
• with BPSK, two phases are possible for carrier wave.
• one phase represents a logic 1 and other a logic 0.
• as the input digital signal changes state (i.e. from 1 to 0 or 0 to 1), the phase of
the output carrier shifts between two phases (that are sepereated by 180) .

16. Remember in PSK, • When information binary signal (modulating signal)
goes low or 0 state, then output carrier undergoes 180o shift with
reference to original carrier for that particular bit slot.
• When information binary signal (modulating signal) goes high or 1
state, then output carrier undergoes 0o shift with reference to original
carrier for that particular bit slot. • PSK modulated output wave will be
shown here

17. Output waveform

18. CATEGORIES OF PHASE SHIFT KEYING
Phase Shift Keying follows M-ARY coding
•BPSK (Binary Phase Shift Keying)
• QPSK (Quaternary Phase Shift Keying)
• 8 PSK

20. Constellation diagram of BPSK

23. Constellation diagram of QPSK

26. THANK YOU