overviewewh.ieee.org/r2/lehigh_valley/sscs/events/06feb2018/slides.pdfcurrent harmonic 1 o lc w= 1...
TRANSCRIPT
RF Harmonic OscillatorsIntegrated in Silicon Technologies
Pietro AndreaniDept. of Electrical and Information Technology (EIT)
Lund University, Sweden
SSCS Distinguished Lecture
Lehigh University, PATuesday, Feb. 6th, 2018
Overview
o Popular harmonic oscillatorsn Phase noise
o Architectures for low 1/f2 and/or 1/f3 phasenoise
o Series-resonance oscillator
o Design techniques for very wide frequencytuning range RF CMOS VCOs
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 2 of 78
LC resonator
We begin with an inductor-capacitor resonator
L CL C
RL RC
01w =LC
RLC
( )0w =Z R0
1w »LC
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 3 of 78
Building a harmonic oscillator
LC
R ‒Ractive
Tank losses are compensated by an activenegative resistance in parallel to the tank
activeR R< 00
RQ RCL
ww
= =
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 4 of 78
Colpitts oscillator
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018
Amplifier + resonator
Feedback network
Noise
Oscillator as positive-feedback system
IB
Vout
VBC1
C2
L R
Amplifier
Resonator
FB
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Colpitts oscillator
IB
Vout
VB C1
C2
L R
Vout
t
Itank
VDD
Itank
VDD
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018
class-C operation
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Classical embodiment of active negativeresistance with only one active device
Analysis with Describing Function
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018
( )( )
01
2 1out
B
A I R n
I R nw= -
» -
C1
C2
Vout
L R
Fundamentalcurrent harmonic
1o LC
w =
1
1 2
CnC C
=+
1 2
1 2
C CCC C
=+
2 BI»0Iw
DSI
t
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Cross-coupled differential-pair oscillatorExtremely popular oscillator family
V-
IB
N1 N2
V+
VDDIB IB
t
t
V-
V+
VDD
Operation in class-B
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018
22BRA A I
p+ -= =2
diff BA I Rp
=
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Class-B with double switch pair
Compared to single-switch-pair:double amplitude, but also doubleVDD (no swing above VDD)
4diff BA I R
p=
V-V+
IB
t
VDDV+ V-
IB
-IBt
VDD
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 9 of 78
Overview
o Popular harmonic oscillatorsn Phase noise
o Architectures for low 1/f2 and/or 1/f3 phasenoise
o Series-resonance oscillator
o Design techniques for very wide frequencytuning range RF CMOS VCOs
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 10 of 78
Real oscillations
o Phase uncertainty grows with time à jittern Caused by various noise sources
o Jitter increases without bound in a free-runningoscillator
o In the frequency domain, the oscillator displaysphase noise
Phase noise,in dBc/Hz
f0 f
dBc
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 11 of 78
Why bother?
Phase noise in transceiver is important for at least threereasons:q In a receiver, it can downconvert large nearby
signals on top of the desired signalq In a transmitter, it can increase the noise floor in
the receive bandq In both, it can directly corrupt the phase
information in the signal– Not seldom, the phase noise of the VCO is the
bottleneck for the whole radio performance
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 12 of 78
Reciprocal mixing
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018
Noise floor raised by mixing of LO phase noise with blocker
0 f1fo
fo+ f1
LO
Desired signal + Blocker
IFfo
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LO
Phase noise and SNR (EVM)
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018
02
BW BW
BWSNR PN PN
-= =ò ò
2010SNR
EVM-
=
Example: 64QAM inWCDMA RX; EVM = 2.5%
f
PN
BW
PLL phase noise
Error vector magnitude
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Phase noise – LTI approach
( ) ( )211 ww w
w w
-æ ö= + + - =ç ÷
è øact
LCY G j C G
j L j L
( ) 0 0 00
0 0
122 2
w w ww w
w w ww w
+ D = = × × = ×D D D
L LZ R RR Q
( ) ( )( )( )
0 00 2
0
0
1 2
w w ww w
ww ww
+ D+ D » » -
D- + D
j L LZ jLC
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018
LC
R ‒Ract
LC tank
Active device
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Phase noise from tank losses
LC2
ni
( )2 22 2
2 0 00
14 42 2
n nB B
v iZ k TG R k TR
f f Q Qw ww w
w wæ ö æ ö
= × + D = × × = ×ç ÷ ç ÷D D D Dè ø è ø
q Both amplitude and phase noise, but amplitude noise is rejectedq Thus, phase noise is defined as half the above expression, normalized
to the output signal power (in dB below the carrier per Hertz, dBc/Hz):
( )22
010 102 2
2 2 110log 10log2 2 2
n B
pk pk
v k TRLA A Q
ww
w
æ ö æ öæ öç ÷ ç ÷D = = ×ç ÷ç ÷ç ÷ Dè øè øè ø
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 16 of 78
Leeson’s equation
( )2
010 2
2 110log2 2
www
æ öé ùæ öç ÷D = ×ê úç ÷ç ÷Dê úè øë ûè ø
B
pk
k TRLA Q
( )L wD
( )log wD
Ideal ( )wDL
Thermal noise (20 dB/dec, 1/f2 region)
F
0
2Qw
Noise floor
1+
31 fwD
Up-converted 1/f noise (30dB/dec, 1/f3 region)
311w
w
æ ö× +ç ÷ç ÷è
D
øDf
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 17 of 78
Hajimiri and Lee’s theory of phase noise
( )td t- ( )outV t
Conversion of noise intophase noise is time-dependent – LTV phasenoise analysis needed!
Hajimiri and Lee, JSSC Feb. ‘98
LC
outV
( )td t-
DV
outV
( )td t-
DV
No phase noise Maximum phase noise
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 18 of 78
Impulse sensitivity function (ISF, G)
q Current noise source is weighed by associated
à effective current noise
q ISF is dimensionless, frequency- and amplitude independent,with period 2p:
( )ni f ( )ni
fG
( ) ( ) ( ), nn eff n ii if f f= ×G
( ) ( )0
1cos
2 n nn
c c nf f f¥
=
G = + +å
( )0tf w=
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 19 of 78
Phase noise expression
( )( ) ( )
2, ,
2 210log
2n eff rms
pk
iL
CAw
w
æ öç ÷D =ç ÷Dè ø
If is a (cyclo)stationary white current noise source,its contribution to 1/f2 phase noise is
( )ni f
( )( )cos w f+pkA t t+
-( )ni f
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 20 of 78
Graphical interpretation
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 21 of 78
Example of ISF – LC oscillators
( )sin fG = -ni
( )cos f=out pkV A
f
f
Hajimiri and Lee, JSSC Feb. ’98; Andreani and Wang, JSSC Nov. ‘04
+
-( )ni f outV
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 22 of 78
A particularly simple caseParallel RLC resonator again
( )( ) ( ) ( ) ( )
( ) ( )
22,
2,,
2 22 2
2 2
10log 10log2 2
4 1 210log2
ww w
w
æ ö æ öç ÷ ç ÷D = =ç ÷ ç ÷D Dè ø è ø
æ ö×ç ÷=ç ÷Dè ø
Gnnn eff rms
pk pk
B
p
rm
k
i siiL
CA CA
k TG
CA2
02
2 1 10 log2 2
ww
æ öæ öç ÷= ç ÷ç ÷Dè øè ø
B
pk
k TRA Q
LC
2n
i
Leeson with F=1recovered without anyad hoc assumptions!
– phase noise from tank losses:
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 23 of 78
Phase noise from MOS pair
V-
IB
N1 N2
V+
Two commutations in one oscillation period
( ) ( )21 , 14N B n m Ni k T gf g f= ( ) ( ) ( )2 2 2
1, 1 1N eff N Ni if f f= ×G
F-
1NI2NI
F
( )1 1N fG »
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 24 of 78
Total phase noise
( )( )
( )22 2tank
10log 1Bn
k TLRA C
w gw
é ùD = +ê ú
Dê úë û
q Transistors appear only through channel noise factor gn
q Transistor phase noise always proportional to tank noise(60% from tank, 40% from MOS pair, if gn = 2/3)
q This is because: 1) transistor noise is proportional tocommutation time, 2) which is inversely proportional to theoscillation amplitude, 3) which is proportional to the tankparallel resistance
q A simple-minded LTI analysis would yield very wrongpredictions (i.e., MOS phase noise increases with MOS gm)
Tank MOS pair
1 nF g= +
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 25 of 78
MOS phase noise – invariance
( ) ( )21 , 14N B n m Ni k T gf g f=
tank
21 Bn
n
IA b
F =
Two effects balance each other:1) Larger MOS produces more
noise during currentcommutation, and
2) Larger MOS allows a fastercommutation
Result: the two areas areidentical
nF,2n bFn-F ,2n b-F
2 nb´
Andreani et al., JSSC May ‘05
1 nb´
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 26 of 78
Single-ended Colpitts oscillator
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018
Hajimiri and Lee, JSSC Feb. ‘98; Andreani et al., JSSC May ‘05
IB
VoutVB
C1
C2
L R( )MOS fG
( )2MOSi f
( )2,MOS effi f
Noise injected into tank when ISF is near zero à excellent!
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Phase noise in Colpitts oscillator
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018
( )( ) ( )22 3 22
1101
log 14
w gw
é ùæ öD » +ê úç ÷è øD
-
-ê úë û
Bn
B
k TLI R C
nnn
However, contrary to what was once (justifiably) believed,Colpitts is more noisy than the differential-pair LC oscillator!
0.30 for 2 31 3 for 10.36 for 1.5
n
opt n
n
nggg
=ìï= =íï =î
Minimum for:
Andreani et al., JSSC May ‘05
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Harmonic oscillators – a general result
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018
1) G sinusoidal and in quadrature with tank voltage2) Active devices work as transistors3) Transistor current noise proportional to gm
Transistor effective noise depends onlyon tank loss and topology
J. Bank, ”A harmonic oscillator design methodology based on describing functions”, PhD thesis, Gothenburg, Sweden, 2006Mazzanti and Andreani, JSSC Dec. ’08; Murphy et al, TCAS-I June ‘10
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More on inductive vs capacitive losses
o Asymmetry between phase noise fromrC vs rL – depends on (large) gm×rC
o Lost with ”equivalent” parallel tank losseso PN from GM always proportional to PN from
rC and rL together (here, g = 1)Pepe and Andreani, TCAS-II June 2016
rLgm
rCGM
rL = rC
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 30 of 78
Matrix-based Fourier-series LTV approach,starting from
All quantities are functions of w0, 2w0, … , nw0
Alternative phase noise analysis
MGY
+
-ResonatorTransconductor
VI
I V= Yr ur
dI dV= MGuur uuur
and
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018
Pepe and Andreani, TCAS-I Feb. 2017
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Results of new phase noise analysis
o Rigorous analysis under very broad hypothesesn GM pure transconductance; Y linear; GM noise
proportional to GM via g
o Phase noise from GM always in proportion of g:1to phase noise from Y, independently ofresonator and transconductor nature
o Phase noise expressions as functions of V and Yo Closed-form, explicit phase noise expressions if
Q is highn General case of Y resonating at multiples of w0
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 32 of 78
What do these expressions look like?
General equation
( ) ( )( )
( )( )20
10 1 12 2
1 1
1 110log 2 Reg w
ww
*
é ù+ê ú
D = × ×ê ú× D ×ê úë û
uuuuruuur
uuur uuuur uuur
T
BT
L k T LV LVDV LV RV
YΔY
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018
MGY
+
-
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Matrix algebra
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018
1 10 00; ; 0T T
M DV RV DV DV LV M× = = × =uuur r uuur uuur uuur uuur r
MGY
+
-* * * * *
2 0 1 2 3 4* * * *
1 1 0 1 2 3* *
0 2 1 0 0 1 2*
3 2 1 1 0 1
4 3 2 1 2 0
é ùê ú- - - - -ê úê ú- - - - -ê ú= - - - - -ê úê ú- - - - -ê ú
- - - - -ê úê úë û
O M M M M M N
K K
K K
K K
K K
K K
N M M M M M O
Y g g g g gg Y g g g g
M g g Y g g gg g g Y g gg g g g Y g
( ) ( )( )
( )( )20
10 1 12 2
1 1
1 110log 2 Reg w
ww
*
é ù+ê úD = × ×ê ú
× D ×ê úë û
uuuuruuur
uuur uuuur uuur
T
BT
L k T LV LVDV LV RV
YΔY
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Tank with multiple resonances
( ) ( )
( )2 2
110 22
2 21
110log
gw
w
é ù+ê úD = ê úDê úë û
åå
Nn nB
Nn n
n A Rk TL
n A C
n high-Q resonances
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018
( ) ( ) 2
010 102 2 2 2
1 21 110log 10log2 2
g ww
w w
æ öé ù+ æ öç ÷D = = ×ê ú ç ÷ç ÷D Dê ú è øë û è ø
B B
pk pk
k T k TRLA C R A Q
Single resonance à we recover the well-known equation
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Tank resonating at w0 and 3w0
o Steeper V-waveform, but now also R3 contributeso Advantageous only if Q3 (much) larger than Q1
o Difficult to enforce in practicePepe and Andreani, TCAS-I Feb. 2017; Garampazzi et al., JSSC Mar. 2014
( ) ( )( )
2 21 1 3 3
10 22 2 21 1 3 3
1 910log9
Bk T A R A RLA C A C
gw
w
é ù+ +ê úD =ê úD +ë û
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 36 of 78
Double-switch pair vs. single-switch pair
IB
V+ V-
IB
V+ V-
Double-switch (DS) pair oscillator Single-switch (SS)pair oscillator
2SS BA I R
p=
4DS BA I R
p=
What phasenoise difference
should weexpect?
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 37 of 78
DS pair vs. SS pair – phase noise
( )2
02
2 110log 12 2 2
n pBDS
DS
k TRLA Q
g gww
w
æ ö+æ öæ öç ÷D = +ç ÷ç ÷ç ÷Dè ø è øè ø
( ) ( )2
02
2 110log 12 2
BSS n
SS
k TRLA Q
ww g
w
æ öæ öç ÷D = +ç ÷ç ÷Dè øè ø
2 6DS SS DS SSA A L L dB= ® = -
o 60% from tank, 40% from transistorsn If gn = gp = 2/3
o If IB,DS = IB,SS and gn = gp à
Andreani and Fard, JSSC Dec. 2006
(!)
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 38 of 78
DS vs. SS – MOS noise
,n SSF,n DSF,n SS-F ,n DS-F
Area (SS) = 2 · Area (DS)
4 DS transistors makeas much noise as 2 SStransistors!
DS
SS
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 39 of 78
Phase noise vs power consumption
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018
• If IB,SS = 2IB,DS à ASS = ADS à same phase noise
• In this case, VDD,SS = ½ VDD,DS à same powerconsumption
• Thus, same maximum achievable “figure-of-merit”(FoM, phase noise for a given power consumption)
• If VDD,DS = VDD,SS and IB,DS = ¼ IB,SS à ASS,max =2ADS,max à LSS,min = LDS,min ‒ 6dB
• Again, FoMSS,max = FoMDS,max
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power efficiency
Figure of merit (FoM)
( )( ) [ ]
2 20 3 210
BDC mW
QFoML P k T F
w w hw
-D= = × ×
D ×
noise factor
High tank Q crucial for high FoM
Phase noise normalized to power consumption,oscillation frequency, and frequency offset
Andreani et al., JSSC Dec. 2006; Garampazzi et al., JSSC Jul. 2015; Murphy et al., ISSCC 2015
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 41 of 78
SS vs DS – PN and FoM with fixed Vdd
SS
SSmax FoM
DSmax FoM
DS
SS oscillation limitDS oscillation limit
IB 4IBLiscidini et al., ISSCC 2012, JSSC Mar. 2014
PhaseNoise
FoM
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 42 of 78
Current bias – resistive source
V-
IB
N1 N2
V+
Resistor
Very simple biascircuitry
No 1/f noisegeneration
Low-Z source
Significantupconversion of1/f noise fromN1-N2
Abidi and Ismail, ISSCC 2003
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 43 of 78
Current bias – MOS source
High-Z source
Less upconversionof 1/f noise fromN1-N2
Own 1/f noisegeneration
“Tail” current source
VB
V-
IB
N1 N2
V+
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 44 of 78
Impact of parasitic tail capacitance
o Ctail,par + cross-coupledMOS entering linear regionà MOS contribution tophase noise increases,even by a large amount
o Ctail,par good for filtering HFnoise from bias
o But, increase of 1/f noiseupconversion
Ctail,par
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 45 of 78
Overview
o Popular harmonic oscillatorsn Phase noise
o Architectures for low 1/f2 and/or 1/f3 phasenoise
o Series-resonance oscillator
o Design techniques for very wide frequencytuning range RF CMOS VCOs
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 46 of 78
Possible solution – noise filter
o Noise filter: Ctail,par resonateswith Ltail at à MOSswitches see high-Z at
o CBIG filters tail noise and ac-grounds Ltail
o CBIG includes CDB of MOS tailà long and large MOS, low1/f noise
o Drawbacks: narrow-band,Ctail,par must be known withsome precision, extra Ltail
Ctail,par
CBIG
Ltail
02w
Hegazi, Sjöland, Abidi, JSSC Dec. 2001
02w
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 47 of 78
Dramatic performance improvemento 0.35μm CMOSo 1.2GHz, 3.5mA, 2.5Vo Ltail = 10nH, CBIG = 40pFo FoM = 196dBc/Hzo TR?
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 48 of 78
More on tail filtero Many variations on the
same basic themeo Extremely popular!
CBIG
LtailCtail,par
Hegazi, Sjöland, Abidi, JSSC Dec. 2001
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 49 of 78
A recent variation
o Tail/top resonance with Xrfmo Very low PN and great FoM
(up to 195.6dBc/Hz)o 200-400kHz 1/f3 cornerGarampazzi et al., JSSC July 2015
@20MHz
/2
7mW
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 50 of 78
Alternative to tail resonance
Babaie et al., RFIC 2013, JSSC Mar. 2015; Shahmohammadi et al., ISSCC 2015; Murphy et al., ISSCC 2015
o Design tank for differential resonance at andcommon-mode resonance atn Also here, the resonance must track the
resonance – two capacitor banks
02w0w
02w 0w
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 51 of 78
Class-F2 (or, here, F2,3) oscillator
Shahmohammadi et al., ISSCC 2015
o 5.4-7.0GHz; 1V, 10-12mWo Low 1/f3 corner (60-130kHz)o Very good FoM (~191dBc/Hz) at
very low PN (-124dBc/Hz @ 1MHz)o Very low VDD pushing (12-23MHz/V)
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 52 of 78
Implicit common-mode resonance
Murphy et al., ISSCC 2016
o 4.7-5.4GHz; 0.7V, 0.5mWo Low 1/f3 corner (200kHz)o Great FoM (194-196dBc/Hz)
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 53 of 78
A totally different approach – class-C
Mazzanti and Andreani, JSSC Dec. 2008
IB
V+ V-
Ctail
N1N2
bias2 I» ×p0
Iw
biasI»0
IwN 2IN 1I
o Ctail turns class-B into class-C:optimal differential “Colpitts”oscillator
o Ideally, 3.9dB lower phasenoise for the same bias current
o Also here, Ctail filters off high-frequency noise from tail, andincludes tail CDB à long andlarge MOS, low 1/f noise
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 54 of 78
Original prototypeo 4.90GHz < fc< 5.65GHzo 1V, 1.4mWo 193.5dBc/Hz<FoM<196dBc/Hz
fosc = 4.90GHz
fosc= 5.52GHz
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 55 of 78
Design issues in class-C CMOS VCO
o Diff-pair must not enter thelinear region (otherwise, largePN penalty) à shift of MOS DCgate voltage VB (which may begenerated with feedback loop)
o RC bias should not load tank(transformer feedback possible)
o Nevertheless, higher maximumoscillation amplitude in theideal class-B CMOS oscillator
o Class-C very attractive for BJTVCOs
Mazzanti and Andreani, JSSC Dec. 2008; Fanori and Andreani, JSSC July 2013
Ctail
V+ V-
VB
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 56 of 78
Colpitts VCO in SiGe BiCMOS process
Boscolo et al., ESSCIRC 2017
o 18.8-23.1GHz; 4.0V, 17.5mAo PN = -119dBc/Hz @ 1MHz (best)o FoM =188dBc/Hz
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 57 of 78
Overview
o Popular harmonic oscillatorsn Phase noise
o Architectures for low 1/f2 and/or 1/f3 phasenoise
o Series-resonance oscillator
o Design techniques for very wide frequencytuning range RF CMOS VCOs
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018 58 of 78
Oscillation with series resonance
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018
( )0sin wpV t0sin
2pQ V t pwæ ö× -ç ÷
è ø
o Voltage driven
o Gain equal to quality factor à internaloscillation may be much higher than VDD
n Attractive for ultra-low phase noise
o p/2 phase shift between input and output
sr L
C
P. Andreani, L. Fanori, and T. Mattsson, “Series-resonance oscillator,” U.S. Patent 2015 0381 157, 2015
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Phase shift by quadrature
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018
90V 180V
o We disregard the (important) issue of start-up
o Square wave between VDD and GND at LC input
o MOS devices work almost exclusively as switches àchannel resistance in series with the tank’s
Tohidian et al., MWCL Aug. 2015; Pepe, Bevilacqua, Andreani, TCAS-I Feb. 2018
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Phase noise
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018
( )( )
( )( )
( )2
010 102 2
4 4 110log 1 10log 14 4
ww
ww w
é ù é ùæ öê ú ê úD = + = +ç ÷ê ú ê úDè øD Dë û ë û
B s B
pk pk s
k Tr k TL F FQI L I r
o MOS work as switches à previous phase noisetheorems do not apply
o F accounts for 1) MOS are non-ideal switches, and2) they do work as transconductors for a (tiny)fraction of the oscillation period
o Ideally, F is negligible!
2p
= DDpk
s
VIr
Pepe, Bevilacqua, Andreani, TCAS-I Feb. 2018
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Figure of merit
P. Andreani, SSCS DL, Lehigh Univ., PA, 2/6/2018
o Usual dependence on Q2
o Very large power consumption, ultra-low phasenoise (plus quadrature phases for free)
o However:n MOS resistance is critical (current-based architectures such
as class-B and class-C are much more robust)n Stray resistances of GND and power supply distribution are
also criticaln Very large internal voltages make frequency tuning difficult
23 210
1h-= × ×+B
QFoMk T F
Ideally, close to 1
Ideally, close to 0
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Overview
o Popular harmonic oscillatorsn Phase noise
o Architectures for low 1/f2 and/or 1/f3 phasenoise
o Series-resonance oscillator
o Design techniques for very wide frequencytuning range RF CMOS VCOs
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VCOs in modern radios – I
o Carrier aggregation requires several harmonicVCOsn Active at the same timen Should not pull one another
o Band proliferation favors VCOs with a very widetuning range (TR)n Wider than 1 octave is particularly attractive
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VCOs in modern radios – II
o VCO with 8-shaped tank inductorn Much less sensitive to external magnetic fieldsn Generates itself a vanishing magnetic fieldn Slightly lower Q acceptablen Often used
M. Nilsson et al., ISSCC 2011
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Very-Wide-TR VCOs – I
o Two or more VCOs with overlapping TRsn Saves power, costs area
n Very popular choice in real-life products
Hadjichristos et al., ISSCC 2009
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Very-Wide-TR VCOs – II
o Large switchable C in parallel to small Ln floating switchesn power wasted at low frequencies, compared to reasonable
phase-noise specsn power cannot be decreased without killing the oscillation
Sjöland, TCAS-II May 2002
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Very-Wide-TR VCOs – III
o Switchable Ln Ultra-wide TR possiblen Difficult to obtain low PN at high FoMn Additional issue: switchable 8-shaped
inductor
Sadhu et al., CICC 2009
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Very-Wide-TR VCOs – IVo Transformer-based VCOs
n Two resonances with overlapping TRsn TR > 1 octaven Difficult to design an 8-shaped transformer
Bevilacqua et al., TCAS-II Apr. 2007; Li et al., JSSC June 2012
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Very-Wide-TR VCOs – V
o Mode-switching VCOn 4 inductors, two oscillation modesn Rejects external magnetic fieldsn TR > 1 octaven Excellent PM and FoMn Large area
Taghivand et al., ISSCC 2014
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Very-Wide-TR VCOs – VIo Double-core VCO
n Two concentric 8-shaped coils – do not interfere (much)with each other
n TR > 1 octave; saves inductor area, sub-optimal Q
Fanori et al., ISSCC 2014
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Very-Wide-TR VCOs – VII
o Reconfigurable active coren Standard LC tank design (i.e., with very large capacitance)n Negative resistance: either single-switch (nMOS) pair –
SS moden or, double (complementary nMOS-pMOS) switch pair –
DS moden DS mode avoids power waste at lower frequencies
Liscidini et al., ISSCC 2012, JSSC Mar. 2014
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SS pair vs. DS pair, again
SS
SSmax FoM
DSmax FoM
DS
SS oscillation limitDS oscillation limit
IB 4IB
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Very-Wide-TR reconfigurable VCO
SS
SSDS
SS
SSDS
Fanori et al., RFIC 2015
o STM 28nm UTBB FD-SOI CMOSo 2.8-5.8GHzo -154<PN (dBc/Hz @20MHz)<-142o 186 < FoM (dBc/Hz) < 189o 300kHz < 1/f3 corner < 3MHz
Phase noise DS-mode, IDC = 4 mAPhase noise SS-mode, IDC = 8 mA
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Conclusions
o Rigorous phase noise resultsn For transconductor-based oscillators
o Class-B VCOs à simple, robust, ubiquitousn Tail filter improves phase noise, even largelyn Recent proposals: common-mode tank resonance at
o Class-C VCOs à better efficiency than standardclass-B, but more complicatedn Class-C must be enforced for all working conditionsn Excellent for BJT VCOs
o Series-resonance oscillator à great potential, butimportant issues to be solved
o Several techniques for very wide frequency tuningrangen None is a clear winner
02w
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