1. 1 11 Lecture 8 Basic Modulation Techniques (IV) Fall 2008 NCTU EE Tzu-Hsien Sang

2. 2 2 Outlines Linear Modulation Angle Modulation Interference Feedback Demodulators Analog Pulse Modulation Delta Modulation and PCM Multiplexing 2

3. 3 FM (Single Tone Wide-band Modulation)

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6. 6 Indirect FM Direct FM Voltage-Controlled Oscillator

7. 7 Demodulation of Angle-Modulated Signals Ideal frequency discriminator: a device that yields an output proportional to the frequency deviation of the input.

8. 8 Approximation: To reduce the channel noise effect, an amplitude limiter and a BPF are placed before the differentiator --- a band-pass limiter.

9. 9 Implementation examples: To approximate the transfer function of an ideal differentiator.

10. 10 Interference Why study interference? The short answer: we don’t have the ability to study noise yet. Let’s start with something simpler. Interference means unwanted signals present in the signal path. Recall the possible causes of interference. Deterministic interference can be analyzed without using stochastic tools.

11. 11 Interference in Linear Modulation

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14. 14 The threshold effect: when the interference is greater than a certain level, the message is totally lost. It’s a non-linear phenomenon.

15. 15 Interference in Angle Modulation

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