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EE104: Lecture 23 Outline

EE104: Lecture 23 Outline. Announcements 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

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EE104: Lecture 23 Outline

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  1. EE104: Lecture 23 Outline • Announcements • 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 • 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) … … f fc -4fm fc+fm fc -3fm fc+3fm fc fc -2fm fc+2fm fc+ 4fm fc-fm 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. 1 0 1 1 0 1 0 1 1 0 On-Off Polar Tb t t

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

  6. r(nTb)+N DN r(nTb) 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 “1” or “0” r(nTb) s(t)  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.

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