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Amin ArbabianJan M. Rabaey

Lecture 2:Transceivers and Signal Modulation

EE142 – Fall 2010Introduction

Aug. 30th, 2010

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Administrative Stuff

HW 1 posted, due September 7th, 5pm

– Not as long as it looks, but start early!

Lab sessions have started

Siva’s OH (481 Cory Hall)- This week only:

– Tuesday 10-11 am

– Wednesday 2:30-3:30pm

My OH: Tu 1-2pm, Th 2:30-3:30pm, 550 Cory Hall– Or by appointment (arbabian@eecs)

Lecture notes available before each lecture

– Will also have in-class notes uploaded after lectures

– Most lecture material from Professor Niknejad

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Modulation

Involves two waveforms:– Modulating signal

– Carrier wave (or just carrier)

Alters the carrier wave with properties of the modulating waveform. The carrier carries the information.

Reversible (Demodulation)

Generally a CW carrier is modulated (also have pulse modulation)

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Why Modulate?

Ease of radiation– Antenna size ~ ⁄

Overcome HW limitations– Fractional BW

Frequency assignment

Multiplexing

Reduced noise and interference– Trade BW for SNR (e.g. early FM)

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AM Modulation- Can’t get simpler than this!

In AM modulation– 1 cos

cos– is the Envelope of the signal

Spectrum of the signal– ⁄⁄

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Time-Domain Waveform

Modulation Index:

Carrier added to the signal (1+x(t)), is this efficient? What are the benefits?

Overmodulated Signal

From Clarke, Hess

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Demodulation

Envelope Detector:

From Clarke, Hess

RC too large: Failure-to-Follow distortion

What if RC is too small?

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Other Amplitude Modulation Schemes

DSB Modulation: Removing the carrier tone:

– cos cos– Improves the power efficiency on transmitter

SSB: Removing one of the side-bands

– Improving the Spectral Efficiency

– Poor low frequency response

VSB: One sideband plus a trace of the other

– For practical transmission of signals with significant low frequency content (e.g. video)

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Phase/Frequency Modulation (“Exponential Modulation”)

“Linear” modulation schemes:– Modulated spectrum

translation of signal spectrum

– BW 2

In exponential modulation these will change. We have also an opportunity to trade BW for signal to noise ratio (Quality).

AM

FM

PM

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FM/PM Modulation

FM Modulation≡ .

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PM Modulation≡ ∆.

∆.

From: Communication Systems by Carlson

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Special Case: Narrowband FM Approximation

From: Communication Systems by Carlson

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Simple FM Transmitter/Receiver

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Using Digital Signaling

On-Off Keying (OOK)

Binary-Shift Keying (BPSK)

Frequency-Shift Keying (FSK)

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A Modern Receiver

Digitize Signals

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A Superheterodyne Transmitter

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Received Signal Strength

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Impedance Matching

If we have a source with certain ‘internal’ impedance, what are the conditions for extracting the maximum power?

What is the maximum “available” power from the source?

Do we always need to match the impedances?

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Receiver Selectivity: Filtering

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Filtering in Receivers

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Transmitter Spectrum

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Frequency Synthesis

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Key EE142 TOPICS

Linear Time Invariant Circuits

Noise

Distortion

Linear Time Varying Circuits

Oscillator

Power Amplifiers

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Wideband and High-Frequency Amplifiers:Linear Time-Invariant Circuits (LTI)

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Noise

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Distortion

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Linear-Time Varying Circuits (LTV)