The document discusses modems and their functions. It begins by defining a modem as a device that modulates and demodulates signals to allow computers to communicate over telephone lines. It then describes the main components of a modem: 1. Modulation: The process of varying a carrier signal to encode digital data for transmission. 2. Demodulation: The process of extracting the original digital data from the received modulated carrier signal. 3. Analog to digital and digital to analog conversion: Processes that allow analog signals to be transmitted over phone lines by converting between analog and digital formats. The document goes on to discuss different types of modulation, demodulation, and conversion techniques in more detail.

1. “MODEM
& IT’S
FUNCTION”
Subject: Digital Logic Design
Submitted to: Sir KamranShah
Submitted by: Sania Bilal
Roll No: BCSF19BM005
Date: 11th June 2020
University of Sargodha Bhakkar Campus
Title:

2. Contents:
 Introduction to Modem
 Modulation
 Demodulation
 Analog to digital conversion
 Digital to Ana log conversion

3. Modem:
• Modem stands for Modulator and Demodulator.
• Allow a computer to communicate over a telephone line.
• The goal of modem is to produce a signal that can be transmitted easily and decoded
to reproduce original data signal.
• It has two working phase:
1. Modulation
2. Demodulation
• There are two types of modem:
1. Internal Modem
2. External Modem
• It can be used over any means of transmitting analog signals
from light emitting diodes to radio.

4. Types of Modem(According to use):
 External Modem
 Internal Modem
 Wireless Modem in PC
 Cable Modem
 Satellite Modem
 ADSL Modem

5. External Modem: Internal Modem:
An external modem is a
network device that is in a self-
contained enclosure external to
a computer. This is in contrast
to an internal modem that is
contained on a printed circuit
board with a computer.
An internal modem is basically an
external modem and serial port
mounted upon a PC bus card. These
are cheaper than
external modems as they do not
require a power supply or a
chassis. Internal modems work fine
for remote serial console
applications.

6.  Wireless Modem:  Cable Modem:
A wireless modem is a modem that
bypasses the telephone system and
connects directly to
a wireless network, through which it
can directly access the Internet
connectivity provided by an Internet
service provider (ISP).
A cable modem is a type
of network bridge that provides bi-
directional data communication
via radio frequency channels on
a hybrid fiber-coaxial (HFC), radio
frequency over glass (RFOG)
and coaxial cable infrastructure.

7.  Satellite Modem:  ADSL Modem:
A satellite modem or sat modem is
a modem used to establish data
transfers using a
communications satellite as a relay.
A satellite modem's main function is
to transform an input bit stream to a
radio signal and vice versa.
Asymmetric digital subscriber line
is a type of digital subscriber line
technology, a data
communications technology that
enables faster data transmission
over copper telephone lines than a
conventional voice band modem
can provide.

8. Types of Modem(According to working function):
 Directional capacity:
half duplex modem and full duplex
modem.
 Connection to the line:
2-wire modem and 4-wire modem.
 Transmission mode:
asynchronous modem and synchronous
modem.

9. transmission in one direction at a time.
If a carrier is detected on the line by the
modem, It gives an indication of the
incoming carrier to the DTE(Data terminal
equipment ) through a control signal of its
digital interface.
As long as the signal is being received; the
modem does not give permission to the DTE
to transmitted data.
 HALFDUPLEX MODEM
A half duplex modem permits

10.  FULLDUPLEX
 A full duplex modem allows
simultaneous transmission in both
directions.
 Therefore, there are two carriers on the
line, one outgoing and the other
incoming.

11.  2-WIRE MODEM
 2-wire modems use the same pair of wires
for outgoing and incoming carriers.
 The data connection established through
telephone exchange is also a 2-wire
connection.
 In 2-wire modems, half duplex mode of
transmission that uses the same
frequency for the incoming and outgoing
carriers can be easily implemented.

12.  4-WIREMODEM
 In a 4-wire connection, one pair of wires is
used for the outgoing carrier and the other
pair is used for incoming carrier.
 Full duplex and half duplex modes of
data transmission are possible on a 4-
wire connection.
 As the physical transmission path for each
direction is separate, the same carrier
frequency can be used for both the
directions

13.  ASYNCHRONOUSMODEM:
 Asynchronous modems can handle data bytes
with start and stop bits.
 There is no separate timing signal or clock
between the modem and the DTE.
 The internal timing pulses are synchronized
repeatedly to the leading edge of the start pulse .
start

14.  SYNCHRONOUSMODEM:
 Synchronous modems can handle a continuous
stream of data bits but requires a clock signal.
 The data bits are always synchronized to the
clock signal.
 There are separate clocks for the data bits
being transmitted and received.

15. “Modulation
And It’s
Types”

16. Modulation:
• First phase of modem.
• Operation of varying amplitude, frequency or phase of carrier signal accordingly
with the instantaneous amplitude of the message signal is called modulation.
• Modulation = Adding information to a carrier signal.
• Modulation is usually applied to electromagnetic signals: radio waves, lasers/optics
and computer networks.

17.  Modulation System:

18. Types of Modulation:
• Amplitude modulation (AM):
In which
the height -- i.e., the strength or intensity --
of the signal carrier is varied to represent the
data being added to the signal.
• Frequency modulation (FM):
Frequency
modulation (FM) is the encoding of
information in a carrier wave by varying the
instantaneous frequency of the wave. The
term and technology is used in both
telecommunications and signal processing.

19. • Phase modulation (PM):
• Polarization modulation:
• .
In which the
phase of the carrier waveform is varied to
reflect changes in the frequency of the
data. In PM, the frequency is unchanged
while the phase is changed relative to the
base carrier frequency. It is similar to FM.
In which the
angle of rotation of an optical carrier signal is
varied to reflect transmitted data.

20. • Pulse-code modulation:
• Quadrature amplitude modulation
(QAM):
In which an
analog signal is sampled to derive a data
stream that is used to modulate a digital
carrier signal.
Which uses two AM carriers to encode
two or more bits in a single transmission

21.  Why we use modulation?
• Multiple carriers of different frequencies can often be transmitted over a
single media, with each carrier being modulated by an independent signal. For
example,Wi-Fi uses individual channels to simultaneously transmit data to
and from multiple clients.
• To increase the bandwidth of the signals.
• To reduce the antenna size.

22. “Demodulation
And It’s
Types”

23.  Demodulation:
• Demodulation is extracting the
original information-bearing
signal from a carrier wave.
• A demodulator is an electronic
circuit that is used to recover the
information content from the
modulated carrier wave.
• The signal output from a
demodulator may represent
sound (an analog audio signal),
images (an analog video signal)
or binary data (a digital signal).

24. Types of Demodulation:
• AM radio:
o An AM signal encodes the information
into the carrier wave by varying its
amplitude in direct sympathy with
the analogue signal to be sent.
o There are two methods used
to demodulate AM signals:
1. envelope detector
2. product detector
o SSB is a form of AM in which the carrier is
reduced or suppressed entirely, which
require coherent demodulation.

25. • FM Radio:
o It is a process of getting back or
generating original modulating signal
from modulated FM signal.
o It can be achieved by converting the
frequency deviation of FM signal to the
variation of equivalent voltage.
o The demodulator will produce an output
where its instantaneous amplitude is
proportional to the instantaneous
frequency of its input FM signal.

26. “Analog to
Digital
Conversion”

27. Analog to digital conversion(ADC):
• ADC (Analog to Digital Converter)is an electronic
device that converts a continuous analog input
signaltodiscretedigital numbers(binary).
 Analog
o Realworldsignals thatcontainnoise
o Continuousintime
 Digital
o Discreteintimeandvalue
o Binarydigitsthatcontainvalues0or 1

28.  Why is ADCImportant?
 All microcontrollers store information using digital logic.
 Compress information to digital form for efficient storage.
 Medium for storing digital data is more robust.
 Digital data transfer is more efficient .
 Digital data is easily reproducible.
 Provides a link between real-world signals and data
storage.

29.  Flash A/D Converter
 Successive Approximation A/D Converter
 Example of Successive Approximation
 Dual Slope A/D Converter
 Delta – Sigma A/D Converter
 Typesof A/DConverters:

30. “Digital to
Analog
Conversion”

31. Digital to Analog conversion(DAC):
 Digital-to-analog conversion is the process of
changing one of the characteristics of an
analog signal based on the information in
digital data.
 Digital data needs to be carried on an
analog signal.
 A carrier signal (frequency fc) performs the
function of transporting the digital data in
an analog waveform.
 The analog carrier signal is manipulated to
uniquely identify the digital data being
carried.

32.  System diagram of DAC:

33.  Types of DAC:

34. Thank You!