1 Amin Arbabian Jan M. Rabaey Lecture 2: Transceivers and Signal Modulation EE142 – Fall 2010 Introduction Aug. 30 th , 2010 2 Administrative Stuff HW 1 posted, due September 7 th , 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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1
Amin ArbabianJan M. Rabaey
Lecture 2:Transceivers and Signal Modulation
EE142 – Fall 2010Introduction
Aug. 30th, 2010
2
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
2
3
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)