5.1

Chapter 5

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Analog Transmission

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5.2

5-1 DIGITAL-TO-ANALOG CONVERSION

Digital-to-analog conversion is the process of changing one of the characteristics of an analog signal based on the information in digital data.

Aspects of Digital-to-Analog Conversion�Amplitude Shift Keying�Frequency Shift Keying

Phase Shift Keying

Quadrature Amplitude Modulation

Topics discussed in this section:

5.3

Figure 5.1 Digital-to-analog conversion

5.4

Figure 5.2 Types of digital-to-analog conversion

5.5

Bit rate is the number of bits per second. Baud rate is the number of signal

elements per second. �

In the analog transmission of digital data, the baud rate is less than �or equal to the bit rate.

5.6

Figure 5.3 Binary amplitude shift keying

5.7

Figure 5.4 Implementation of binary ASK

5.8

Figure 5.6 Binary frequency shift keying

5.9

Figure 5.7 Bandwidth of MFSK used in Example 5.6

5.10

Figure 5.9 Binary phase shift keying

5.11

Figure 5.10 Implementation of BASK

5.12

Figure 5.11 QPSK and its implementation

5.13

Figure 5.12 Concept of a constellation diagram

5.14

Example 5.8

Show the constellation diagrams for an ASK (OOK), BPSK, and QPSK signals.

Solution

Figure 5.13 shows the three constellation diagrams.

5.15

Figure 5.13 Three constellation diagrams

5.16

Quadrature amplitude modulation is a combination of ASK and PSK.

5.17

Figure 5.14 Constellation diagrams for some QAMs

5.18

5-2 ANALOG AND DIGITAL

Analog-to-analog conversion is the representation of analog information by an analog signal. One may ask why we need to modulate an analog signal; it is already analog. Modulation is needed if the medium is bandpass in nature or if only a bandpass channel is available to us.

Amplitude Modulation�Frequency Modulation�Phase Modulation

Topics discussed in this section:

5.19

Figure 5.15 Types of analog-to-analog modulation

5.20

Figure 5.16 Amplitude modulation

5.21

�The total bandwidth required for AM �can be determined

from the bandwidth of the audio �signal: B_AM = 2B.

5.22

Figure 5.17 AM band allocation

5.23

The total bandwidth required for FM can be determined from the bandwidth �of the audio signal: B_FM = 2(1 + β)B.

5.24

Figure 5.18 Frequency modulation

5.25

Figure 5.19 FM band allocation

5.26

Figure 5.20 Phase modulation

5.27

The total bandwidth required for PM can be determined from the bandwidth �and maximum amplitude of the modulating signal:�B_PM = 2(1 + β)B.

THANK YOU.

Please start preparation for Mid Term Exam.

5.28