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Analog Frequency Synthesizers PDF

103 Pages·2009·1.02 MB·English
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Short Course On Phase-Locked Loops IEEE Circuit and System Society, San Diego, CA Analog Frequency Synthesizers Michael H. Perrott September 16, 2009 Copyright © 2009 by Michael H. Perrott All rights reserved. What is a Phase-Locked Loop (PLL)? ref(t) ref(t) out(t) out(t) e(t) e(t) v(t) v(t) ref(t) e(t) v(t) out(t) Analog Phase Loop Filter Detect de Bellescize VCO Onde Electr, 1932 (cid:131) VCO efficiently provides oscillating waveform with variable frequency (cid:131) PLL synchronizes VCO frequency to input reference frequency through feedback - Key block is phase detector (cid:131) Realized as digital gates that create pulsed signals 2 M.H. Perrott Integer-N Frequency Synthesizers ref(t) div(t) e(t) v(t) F = N F out ref ref(t) e(t) v(t) out(t) Analog Phase Loop Filter Detect VCO Sepe and Johnston div(t) Divider US Patent (1968) N (cid:131) Use digital counter structure to divide VCO frequency - Constraint: must divide by integer values (cid:131) Use PLL to synchronize reference and divider output Output frequency is digitally controlled 3 M.H. Perrott Integer-N Frequency Synthesizers in Wireless Systems Z in PC board From Antenna Mixer trace and Bandpass RF in IF out Package Filter Z LNA To Filter o Interface LO signal VCO ref(t) v(t) out(t) Reference Frequency Frequency Synthesizer ref(t) e(t) v(t) out(t) Charge Loop PFD Pump Filter VCO div(t) Divider N (cid:131) Design Issues: low noise, fast settling time, low power 4 M.H. Perrott Fractional-N Frequency Synthesizers ref(t) div(t) e(t) v(t) F = M.F F out ref ref(t) e(t) v(t) out(t) Analog Phase Loop Filter Detect VCO div(t) Divider Σ−Δ N [k] N[k] M.F sd Modulator (cid:131) Dither divide value to achieve fractional divide values - PLL loop filter smooths the resulting variations Very high frequency resolution is achieved 5 M.H. Perrott Going Digital … out(t) ref(t) Analog Phase Loop Filter Detect VCO Divider out(t) ref(t) Time Digital -to- Loop Filter Digital Staszewski et. al., DCO TCAS II, Nov 2003 Divider (cid:131) Digital loop filter: compact area, insensitive to leakage (cid:131) Challenges: - Time-to-Digital Converter (TDC) - Digitally-Controlled Oscillator (DCO) 6 M.H. Perrott Outline of PLL Short Course (cid:131) Analog frequency synthesizers - Integer-N synthesizers and PLL background - Fractional-N synthesizers (cid:131) Digital frequency synthesizers - Modeling and noise analysis - Time-to-digital conversion 7 M.H. Perrott Outline of Integer-N Frequency Synthesizer Talk F F = N F ref out ref ref(t) e(t) v(t) out(t) Loop PFD Filter VCO Divider div(t) N (cid:131) Overview of PLL Blocks (cid:131) System Level Modeling - Transfer function analysis - Nonlinear behavior - Type I versus Type II systems (cid:131) Noise Analysis 8 M.H. Perrott Popular VCO Structures LC oscillator VCO Amp V out -R C L R amp V p in Ring oscillator V out V in -1 (cid:131) LC Oscillator: low phase noise, large area (cid:131) Ring Oscillator: easy to integrate, higher phase noise 9 M.H. Perrott Model for Voltage to Frequency Mapping of VCO LC oscillator VCO Amp V out -Ramp Vin C L Rp F vco Ring oscillator V out F out f c VCO V in -1 Frequency slope=Kv v v in V bias Input Voltage 10 M.H. Perrott

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M.H. Perrott 2 What is a Phase-Locked Loop (PLL)? ref(t) e(t) Analog v(t) out(t) Loop Filter Phase Detect VCO ref(t) out(t) e(t) v(t) ref(t) out(t) e(t) v(t)
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