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

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

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)

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 1 0 1 1 0 Polar 1 0 1 1 0 Tb t t

ASK, PSK, and FSK Amplitude Shift Keying (ASK) Phase Shift Keying (PSK) Frequency Shift Keying 1 0 1 1 m(t) AM Modulation 1 0 1 1 m(t) AM Modulation 1 0 1 1 FM Modulation

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)

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.