moddemod8337_2008b

moddemod8337_2008b - Modulation/Demodulation 1 Analog...

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Analog Design Group, University of Minnesota (harjani@ece.umn.edu) 1 Modulation/Demodulation
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Analog Design Group, University of Minnesota (harjani@ece.umn.edu) 2 Modulation/Demodulation ± Analog and digital modulation ± Concerns z Spectral regrowth z Power efficiency ± Modulation ± If a(t) is a constant => constant envelope modulation z Nonlinear modulation ± If a(t) is variable => variable envelope modulation z Linear modulation x ( t ) = a ( t ) cos ω c t + φ ( t ) ( ) Total phase Excess phase total frequency = ω c + ∂φ t
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Analog Design Group, University of Minnesota (harjani@ece.umn.edu) 3 Modulation ± Modulation formats z Amplitude modulation z Frequency modulation z Phase modulation ± Data formats z Analog z Digital ± First let us consider analog modulation ± Next we will consider digital modulation ± Finally we will review multi-carrier modulation formats
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Analog Design Group, University of Minnesota (harjani@ece.umn.edu) 4 Amplitude Modulation ± M=modulation index ± Comments z SNR needs to exceed 25dB z Large transmitted power z Not used extensively anymore (expect in AM radio) z Susceptible to noise z Requires linear power amplifier (PA) wc w am 1.5 1 0.5 0 0.5 1 1.5 x ( t ) am = Ac 1 + mX bb ( t ) [] cos( ω c t )
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Analog Design Group, University of Minnesota (harjani@ece.umn.edu) 5 Amplitude Modulation (cont.) ± Bandwidth of X AM (F) is twice that of X BB (FF) ± If (1+m X BB (t))> 0 then we can use envelope detector Transmitter power Ref: Razavi, RF Microelectronics B=BW of X BB
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Analog Design Group, University of Minnesota (harjani@ece.umn.edu) 6 Phase & Frequency Modulation ± Phase modulation z φ (t) is linearly proportional to baseband signal ± Frequency modulation z d φ (t)/dt is linearly proportional to baseband signal ± Not easy to distinguish between PM and FM particularly for analog modulation ± Analog FM used more commonly x pm ( t ) = Ac cos ω c t + mX bb ( t ) [ ] Phase/Frequency modulation
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Analog Design Group, University of Minnesota (harjani@ece.umn.edu) 7 Digital Modulation ± Binary z ASK z FSK (BFSK) z PSK (BPSK) ± Quadrature z QPSK z OQPSK z π /4-QPSK ± Minimum shift keying z Gaussian minimum shift keying (GMSK)
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Analog Design Group, University of Minnesota (harjani@ece.umn.edu) 8 ASK/FSK/PSK ± ASK ± FSK ± PSK Detectors not as straight forward
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Analog Design Group, University of Minnesota (harjani@ece.umn.edu) 9 BPSK ± BPSK modulator Ref: RF and Microwave Circuit Design for Wireless Communications, L. Larson, 1996
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Analog Design Group, University of Minnesota (harjani@ece.umn.edu) 10 Frequency Modulation (NB) ± Narrowband FM ± Bandwidth occupied by NB FM is less than equal to AM x FM ( t ) = A c cos ω c t + mX bb ( t ) dt −∞ t bb ( t ) dt −∞ t << 1 -wm +wm wc-wm wc+wm
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Analog Design Group, University of Minnesota (harjani@ece.umn.edu) 11 Narrowband FM ± Sinusoidal modulation z Baseband signal z Narrowband FM signal * Easiest to handle if we use Euler’s transformation for Cos and Sin
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Analog Design Group, University of Minnesota (harjani@ece.umn.edu) 12 Wideband FM ± Wideband FM ± Carson’s rule -wm +wm wc-wm
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moddemod8337_2008b - Modulation/Demodulation 1 Analog...

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