Analog Frequency Synthesizers

103 Pages·2009·1.02 MB·English

by  Michael H. Perrott

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
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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
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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
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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
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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)
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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
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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
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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
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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
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