This document discusses amplitude modulation techniques. It covers topics like baseband communication versus carrier communication, amplitude modulation using double sideband modulation, examples of tone modulation and frequency mixing, different types of modulators used for amplitude modulation, and generation and demodulation of AM signals. It also discusses concepts like modulation index and sideband and carrier power distribution in an AM signal. Diagrams and equations are provided to illustrate amplitude modulation and demodulation methods.

1. Amplitude (Linear) Modulation

2. Modulation
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3. 3
Baseband communication vs.
Carrier communication
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4. 4
Baseband communication vs.
Carrier communication
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5. Amplitude Modulation
(Double Sideband DSB)
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10. Example 4.1 (Tone Modulation)
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14. Modulators
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26. Example 4.2 (Frequency Mixer or Converter)
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30. Example 4.3 (Switching Demodulator)
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31. Amplitude Modulation (AM) for
Broadcast System as opposed to
point-to-point communication
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32. Amplitude Modulation (contd.)
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CASE I: If 𝑚 𝑡 ≥ 0 for all 𝑡
then 𝐴 = 0 also satisfies the condition, no need to add any carrier
because the envelope of the DSB-SC signal 𝑚 𝑡 cos 𝑤𝑐𝑡 is 𝑚(𝑡) and
such a signal can be detected by envelope detection.
CASE II: If 𝑚 𝑡 ≱ 0 for all 𝑡
Let 𝑚𝑝 be the peak amplitude (+ive or –ive) of 𝑚(𝑡). This means that
𝑚 𝑡 ≥ −𝑚𝑝. The above condition is 𝐴 ≥ 𝑚𝑝. Thus the minimum carrier
amplitude for the viability of envelope detection is 𝑚𝑝.
AM Demodulation using Envelope
Detection
𝐴 + 𝑚 𝑡 ≥ 0 for all 𝑡
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34. Modulation Index, 𝜇
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𝐴 − 𝑚𝑝 ≥ 0
𝑚 𝑡 ≥ −𝑚𝑝
Condition for Envelope
Detection
𝐴 + 𝑚 𝑡 ≥ 0 for all 𝑡 (1)
𝑡
−𝑚𝑝
𝑚𝑝
𝑚 𝑡
𝑡
𝐴 + 𝑚 𝑡
𝐴
𝐴 ≥ 𝑚𝑝 (2)
𝜇 =
𝑚𝑝
𝐴
0 ≤ 𝜇 ≤ 1
𝑅𝑎𝑛𝑔𝑒
𝑅equired
From (1)
𝑀𝑜𝑑𝑢𝑙𝑎𝑡𝑖𝑜𝑛
𝐼𝑛𝑑𝑒𝑥
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35. Example 4.4
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36. Sideband and Carrier Power
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37. Example 4.5
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38.  AM Signals can be generated using any of the DSB-SC
modulators if the modulating signal is 𝐴 + 𝑚(𝑡) instead of just
𝑚 𝑡 .
 No need to have a balanced circuit, accounts to a simple
modulators for AM.
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Generation of AM Signals
Specifications:
1. Single diode instead of a
bridge
2. Input is [𝑐 cos 𝜔𝑐𝑡 + 𝑚 𝑡 ]
3. Now, 𝑐 ≫ 𝑚(𝑡), Why?
4. Switching action of the diode
is controlled by 𝑐 cos 𝜔𝑐𝑡

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Generation of AM Signals (contd.)

40.  AM Signals can be demodulated coherently by using a locally
generated carrier but will defeat the very purpose of AM. Why?
 Hence, non-coherent methods of AM demodulation is used:
1. Rectifier Detection
2. Envelope Detection
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Demodulation of AM Signals
Rectifier Detector

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1. Rectifier Detector
𝑣𝑅

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