Presentation of Amplitude Modulation and Demodulation with examples

1. Amplitude Modulation and Demodulation
By:
Bikram Modak
Department-Computer Science and Engineering
Semester-4th
Roll no.-11900115013
Registration no.-151190110013

2. Introduction
• Modulation
-In the modulation process, some characteristic of a high-frequency carrier signal
(bandpass), is changed according to the instantaneous amplitude of the information
(baseband) signal.
-It is the simplest and earliest form of transmitters.
• Why Modulation
-Suitable for signal transmission (distance…etc).
-Multiple signals transmitted on the same channel.
-Capacitive or inductive devices require high frequency AC input (carrier) to operate.
-Stability and noise rejection.

3. Amplitude Modulation
• AMPLITUDE MODULATION is formally defined as a process in which the amplitude
of the carrier wave c(t) is varied about a mean value linearly with a message signal
m(t) keeping frequency and phase constant .
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1
-5
0
5
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1
-1
0
1
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1
-1
0
1
• The AM signal
• The Modulating signal
• The Carrier signal
     ttmkAts cc cos1 
 tm
  tAtc cc cos

4. (cont.)
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2
-5
-4
-3
-2
-1
0
1
2
3
4
5
• The Envelope
• The AM signal
     ttmkAts cc cos1 
    tmkAts c  1

5. Amplitude Sensitivity
Modulation Index - The ratio between the amplitudes between the
amplitudes of the modulating signal and carrier, expressed by the
equation:
c
m
E
E
m =

6. AM-Percentage Modulation
Under modulated (<100%)
Envelope Detector Can be
used
100% modulated
Envelope Detector Can
be used
Over Modulated(>100%)
Envelope Detector Gives
Distorted Signal

7. Examples
An Example of message signal m(t) Waveform for Amplitude modulation of the message signal m(t)

8. Amplitude Modulator
Electro-Optic Mode Converter
The Versawave 40 & 50 Gb/s Amplitude Modulators represent a revolutionary method for modulating
CW laser light into data carrying optical pulse trains. By employing proprietary GaAs technology, the
Versawave modulators establish new benchmarks for low drive voltage, ultra-wide bandwidth, and
chirp-free operation within a small footprint.
The innovative and IP protected design of Versawave’s modulators exploit the unique material
properties of GaAs to provide chirp free modulation. By using a unique polarization mode converter
approach, Versawave eliminates many of the intrinsic limitations of designs based on Mach-Zehnder and
other electro-absorption architectures. In addition, the Versawave Amplitude Modulators are able to
deliver best-in-class performance over the entire Telcordia GR-468 environmental range without the
need of a thermo-electric cooler (TEC).

9. (Cont.)
Applications.
• Analog and digital
• SONET OC-768 and SDH STM-256 transmissions
• 40 & 50 Gb/s transponders
• High-speed Internet routers
• DWDM, high-speed Ethernet and TDM
• High-speed test equipment
Features.
• High modulation bandwidth
• Low drive voltage
• Chirp <0.1
• High extinction ratio
• Small footprint
• Optional PIN diode for optical power monitoring and bias control
• Covers C and L Band
• GaAs technology

10. Demodulation
Demodulation is the process of recovering the signal intelligence
from a modulated carrier wave. This process, also called
detection, is the reverse process of modulation.

11. Why Do we Need Demodulation?
-The wireless signal consists of radio frequency (high frequency)
carrier wave modulated by audio frequency (low frequency).
-The diaphragm of a telephone receiver or a loud speaker cannot
vibrate with high frequency. Moreover, this frequency is beyond the
audible range of human ear. So, it is necessary to separate the audio
frequencies from radio- frequency carrier waves.

12. Amplitude Demodulation Process

13. IMPORTANCE OF RECTIFICATION AND
DEMODULATION
• The modulation enveloped on the positive and negative sides are
180o out of phase.
• If rectification is not done, then after filtering, the positive and
negative envelopes would cancel each other .
• So, the original modulating signal cannot be recovered. Thus,
rectification is necessary in demodulation.

14. Types of AM Demodulation
The major types of AM demodulator are:
• Diode AM detector: This is by far the simplest form of AM demodulator or detector,
requiring just a semiconductor (or other form) of diode along with a capacitor to remove
the high frequency components. It suffers from a number of disadvantages, but its
performance is more than adequate for most applications including broadcast receivers
where cost is a significant driver.
• Synchronous AM detector: This form of AM detector offers a higher level of performance,
but at the cost of considerably the use of considerably more components. This means that it
is only used in receivers where the levels of performance are paramount and can justify the
additional component costs.