1. EE104: Lecture 23 Outline Announcements Review of Last Lecture
HW 7 posted, due next Monday at 7pm (no late HWs)
Final exam Thursday March 20 8:30-11:30. Details Wednesday
Review of Last Lecture
FM Detection
Information as Bits
Baseband Digital Modulation
Passband Digital Modulation
ASK, PSK, and FSK Modulation and Detection

2. Review of Last Lecture … … B2Df+2Bm Spectral Analysis of FM
FM Bandwidth and Carson’s Rule
Narrowband FM Modulation
Product modulator
Wideband FM Modulation
NBFM modulation and nonlinear device or VCO
S(f) for m(t)=cos(2pfmt) … …
fc -4fm
fc -3fm f
fc -2fm
fc-fm fc
fc+fm
fc+2fm
fc+3fm
fc+ 4fm
B2Df+2Bm

3. FM Detection Differentiator and Envelope Detector
Zero Crossing Detector
Uses rate of zero crossings to estimate fi
Phase Lock Loop (PLL)
Uses VCO and feedback to extract m(t)

4. Introduction to Digital Modulation
Most information today is in bits
Baseband digital modulation converts bits into analog signals (typically bits encoded in amplitude)
Passband digital modulation has form
Bits encoded in amplitude An, phase n, or frequency n=2p(fn-fc)t, which are constant over a bit time Tb.
On-Off
Polar Tb t t

5. ASK, PSK, and FSK Amplitude Shift Keying (ASK)
Phase Shift Keying (PSK)
Frequency Shift Keying
m(t)
AM Modulation
m(t)
AM Modulation
FM Modulation

6. ASK/PSK Demodulation
Similar to AM demodulation, but only need to choose between one of two values
Decision device determines which of r0 or r1 that r(iTb) is closest to
Noise immunity DN is half the distance between r0 and r1
Bit errors occur when noise exceeds this immunity
Decision Device
nTb r1
r(nTb)
r(nTb)+N
“1” or “0”
s(t)  DN
r(nTb) r0
cos(2pfct)

7. Main Points
In theory just need differentiator and envelope detection for FM. Many techniques used in practice (mostly VCO).
Most information today is in bits
Digital baseband modulation uses simple techniques to encode bits into baseband analog signal.
Digital passband modulation encodes binary bits into the amplitude, phase, or frequency of the carrier.
Decision device in receiver uses threshold to determine which bit was sent.
Bits errors occur when noise exceeds noise immunity threshold.