transceivers architectures for mobile & wireless applications
TRANSCRIPT
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Wireless Transceiver Challenges
• Stringent linearity, phase noise, selectivity on RX
• Stringent mask, far-out noise on TX
WirelessReceiver
Desired TX
Interferer TXIn-band
N×200kHz in GSM
Select the desired channel
10
0d
B
Ou
t-o
f-b
and
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Receiver Requirements
• Small signal linearity:
IIP2, IIP3
Y
XABAD
Operates here
GGD
fB1 fB22fB1-fB2• Large signal linearity:
Gain compression
• Reciprocal mixing: BNF = 174 – PB -PN
• Harmonic mixing
• Receiver NF sets the sensitivity, range:
Set by the standard10Log(KT), dBm/Hz
Sensitivity = -174 + NF + 10Log(BW) +SNRRS=50ΩΩΩΩ
RX
Blo
cke
rs: I
n/O
ut-
Ban
d
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Transmitter Requirements
• Far-out noise
• Modulation quality: PE, EVM
10
dB
/
100kHz/
–Sets the modulator quality
–Sets the TX linearity
–Determines TX phase noiseGSM Mask
• Output power
• Spectrum Mask
• Phase noise intransceivers:
NF: Range
Blockers:Co-existence
SNR: Thru-put
Ph
ase
No
ise
Frequency
SNR, EVM
Mask, Blockers
Far-out noise
RX
Eq
uiv
alen
t
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• CDMA less sensitive to jammers:
Code: 3.84MHz
TX Out
Code
RX IN
GSM/EDGE/WCDMA
Modulation Bands Thru-put Challenges
GSM GMSK: 270kbps 4 0.08 Blockers, TX mask, phase noiseEDGE 8PSK: 810kbps 4 0.236
3G+1 QPSK … 64QAM 19 0.384-21 TX leakage
• GSM/EDGE is TDMA, while 3G is CDMA. Both FDD.
1 HSPA, HSPA+, up to 21Mbps thru-put
Slot0 Slot1 Slot7 Frame: 8×577µµµµS…
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RF IC
Large Blocker
Duplexer
RX Desired
TX Leakage
3G Full-Duplex Problem
• Duplexer is a dual-band filter
TX RX
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Concept of MIMO
• Signals received on multiple antennas combined to create a more benign composite channel
– Combined signal energy increases SNR
– Variability across frequency reduces fading
• Trading robustness for rate
S1
S2 Dem
od
ula
tor
DiversityCombiner
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• Flexible bandwidth and modes
–Over 40 bands
–1.4 -20 MHz variable bandwidth
–Flexible FDD, TDD, & FDD half duplex
• High mobility up to 120 km/h
• Carrier aggregation in LTE-A: 1Gbps
LTE Features
Band A Band B
• High data rate: DL 300Mbps, UL 75Mbps
RX1
RX2
RX3
RX4
LO1
LO2
Intra-Band
Inter-Band
Contiguous Non-Contiguous
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WLAN Design Challenges
• Bandwidth variability and detection
– 20MHz up to 160MHz
– OFDM
• Receiver SNR and IQ imbalance
– LO (fixed) & filters (variable over frequency)
– Sensitivity: -67dBm for .11g, SNR = 25dB: NF =9dB
• TX PAR of 12dB for 64QAM
• High fidelity transmitters
– -28dB EVM for 64QAM
– IQ and in-band phase noise
0f
To help multi-path
I
Q
.3125M
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Ideal Transceiver
AD
CD
AC
SDRBB
fIF = fIN - fLO
IF
fLO
RF
• Filter only rejects out-of-band blockers
• In-band blockers require a high-resolution ADC
• Power hungry
• Invented by Armstrong in 1918
• Frequency-conversion
relaxes IF signal processing
• Lower power
-99dBm
0dBm-26dBm
AD
CD
AC
7 Armstrong, 1924 10 Mitola, 2005
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LO Harmonic Mixing Issue
• In a perfectly linear RX, blockers still problematic
fLO nfLO
fIFfIF
• Sets LNA IIPk , filter attenuation, range of acceptable IF
PD
PB
(nf L
O±f
IF)/
k
fLO nfLO3fLO
…
Hard Switching Mixer
IIPk
15 Cijvat, TCAS 2002
• Image: n=k=1, Only removed by filtering
• Half-IF: n=k=2, Differential helps fLO
fIF/2
(2f L
O±f
IF)/
2
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Super-Heterodyne Receiver
• Down-conversion relaxes the ADC
• High IF avoids DC offset & low frequency noise
• Needs external filters for image and other blockers
On-Chip
Pre-Select
Channel-Select
fLOIF
Image Reject
7 Armstrong, 1924
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Zero-IF Receiver
• Less severe image issue
• Channel selection on-chip
• Suitable for WB: LTE, WiFi
Channel-SelectIQ
• Requires quadrature LO
• DC Offset, 1/f noise, IIP2
• In band IRR
Pros Cons
1 Abidi, JSSC 1995
ωωωωLO-ωωωωLO
0
Complex
f1
/f n
ois
e OFDM
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• For 12.2kbps reference measurement, SF=128, -117dBm sensitivity, required NF = 9dB
DPCH_Ec = -117dBm/3.84Mz
I^or = -106.7dBm/3.84MHz
Noise Floor = -108dBm(-174,3.84MHz)SF+CG=25dB
SNR = 7dB-99dBm
• For a given duplexer, NF depends on:
–RX thermal noise
–RX 2nd-order nonlinearity
–TX and PA noise at RX band
NF
3G RX NF Requirement
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• TX leakage amplitude demodulated at zero IF
• In order not to affect sensitivity IIP2 > 50dBm
A(t)Cos(ωωωωt+φφφφ(t))
A(t)2
3G IIP2 Requirements
fTX fRX
0
+24dBm
…
+28dBm
I ≈50dB
IIP2 = 2×(28dBm-I) – 13dB – -99dBm -10dB = +52dBm
Desensitizes by 0.5dB
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• Stringent IIP3 due to TX leakage:
TX
3G Out-of-Band IIP3 Requirements
PTX PB
(fRX-fTX)/2
28-50 -15-30-99+3-5
• IIP3 = -5.5dBm at the LNA input
• Need room for TX noise, 2nd-order nonlinearity …
Duplexer Isolation: 50dBDuplexer Filtering: 30dB
…
Signal = PTX + 2×PB - 2×IIP3
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Low-IF ReceiverLow-IF
fLOI
fLOQ Act
ive
Po
lyp
has
e• IIP2, 1/f less problematic
• Image in-band
• Suitable for NB: GSM, BT
• Requires quadrature LO
• Higher IF, higher power
• Tighter IRR
Pros Cons
0 IF∝∝∝∝BWIR
Digital IR
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GSM Noise Figure
• Most advanced receivers target for <-109dBm
• NF of < 3dB assuming 3dB loss at front-end
• The standard requires -102dBm
• Receiver NF sets the sensitivity:
≈ 59dB for GMSK
Sensitivity = -174 + NF + 10Log(BW) + SNR…
≈3dB
Band X
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Choice of IF: Adjacent Blockers
•Trade-off between 1/f noise, IIP2, … vs. image rejection
12
0
14
0
16
0
18
0
IF, kHz
IMR
R, d
Bc
30
35
40
45
Desired
20
0k
60
0k
40
0k
-73dBm
-41dBm
-82dBm
-33dBm
fLOIF
n×200k
IF
n×200k-2×IF
Mostly 200k
Tail of 400k
400k
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GSM In-Band Blocking Requirements
Desired
60
0k
1.6
M
3M
-43dBm
-99dBm
-23/-26dBm
• LO PN of -140dBc/Hz at 3MHz
• BNF = 174 – 26 – 140 = 8dB
• RX NF of 6dB: Total BNF ≈ 10dB
• 3GPP NF requirement: 13dB
• Compression degrades the BNF further
– -26/-23dBm blocker can heavily compress the front-end
PD
PBSNR
BWfLO
∆∆∆∆fB
Noisy LO
BNF = 174 + PB + PN
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Dual-Conversion Receiver
• DC offset and 1/f noise issues less severe
• No high frequency quadrature LO
• Higher power due to 2 mixers in signal path
• First LO image
Zero or Low-IF
fLO2I
fLO2Q
fLO1
fLO2 = fLO1/N
Sliding 1st IF = fRF / N+1
13 Zargari, JSSC 2002
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Gain Control & Receiver SNR
• SNR determines through-put at high input powers
P1
dB, d
Bm
-11
2
-97
-82
-67
-52
-37
-22
Input, dBm
• Front-end gain reduction improves P1dB
• But degrades SNR
0
10
20
30
40
-112
-97
-82
-67
-52
-37
-22
Input, dBmSN
R, d
B PN, IQ& linearity
Gai
n, d
B
In-bandAdjacent
Ideal Slope
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RF PGA1 PGA2
-90
-60
-30Blocker
Sign
al, d
Bm
AD
C
ADC
Q-Noise
ADC and Filtering
U/D fading
• GC keeps desired signal
close to ADC full scale
• Trade-off between filter
& ADC
• ADC DR >> receiver SNR
Signal
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Example: 2G ADC Requirements
• -400kHz blocker dominant in low-IF
ADC Full Scale
Up Fading
Blocker
Down Fading
87dB
Margin: GC
10dB
6dB
41dB
10dB
ADC Q Noise
20dB Noise Margin
Blocker
Signal(57dB below FS)
(SNR ≈ 6dB)
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Out-of-Band Blocking Issue
External SAW filters attenuate out-of-band blockers
The in-band blocker as high as -23dBm
19
90
20
10
20
70
-23/6dBm
-12dBm
0dBm
19
30
-99dBm
PCS Band1
91
0
18
30
GSM out-of-band blocker profile:
Frequency, MHz
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Narrow-Band Filtering Concerns
• Large blockers compress the receiver
• Impose stringent far-out phase noise
• External filtering is narrow-band and costly
Mu
lti-
Ban
d R
ece
ive
r
Swit
ch
…
-99dBm
0dBm
15-20dB
6.6V p-p
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Passive Mixers as N-Path Filters4
)()(2
)(2 LOBBLOBBSWin jsZjsZRsZ ωω
π++−+≈
LO1
LO2
LO3
LO4
0
IRF
VRF
0
High-Q BPF from low-Q LPF
fLO
fLO
LO1
LO4
0
LO2
LO3
VRF
IRF
ZBB
4 L. Franks, Bell Syst. Tech. J., 196014 Mirzaei, TCAS 2010
Blo
cke
r
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Current-Mode Receivers
• Passive mixers to achieve high-Q filtering
• Current mode LNA: LNTA
• Enhance the blocker tolerance
21,22 Mikhemar, VLSI 2012
GM
0fRF
fRF
0
BUF
BUF
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Mixer-First Receivers
• At high frequency noise aliasing degrades NF significantly
• NF > 4dB in practice at GHz frequencies 18,19 Andrews, JSSC 2010
LO1
LO2
LO3
LO4TI
A_I
I
TIA
_Q Q
RS
VS
SW Resistance, ΩΩΩΩ
NF,
dB
0
1
2
3
4
5
0 10
20
30
40
50
gAlia
S
bb
S
DS NKTRM
v
R
ONrF
sin
2
)4(
)(1 ×
++=• For M phases:
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Noise Cancelling Receivers
• Low noise and linear
• No Balun required
RS
RS = RSW + 2RBB/ππππ2
-+
BW << ∆∆∆∆fB
-+
GM αααα = -GM×RLA+
VOUT
-
Low resistance
Noise and linearity bottleneck
RLA
RLM
rm = RLM
26 Murphy, ISSCC 2012
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Over-Sampling Mixer Architecture
• Square-wave LO harmonically rich
• Synthesizes arbitrary 8-phase LO:
TIA K0
TIA K1
TIA K7
ΣΣΣΣVOUT
…
IRF
8-P
has
e
√2
Harmonic Combination
∑=
−=7
0
)8
()(x
xRFOUTT
xtswKtiV
1
1/7
17 Weldon, JSSC 2001
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Case Study: NC SDR Receiver
GM
10ΩΩΩΩ
50ΩΩΩΩ
I
Q
We
igh
tin
g &
Re
com
bin
atio
n
…LO0LO1
LO7
4fLO ÷4
NF ≈ 1 + γγγγ/GMRS
26 Murphy, ISSCC 2012
• 1.9dB NF, 4dB BNF
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Direct-Conversion Transmitters
• Low power
• Versatile
• Highly integrated
• Suffers from pulling
• LOFT, IQ matching
• Far-out noise
Pros Cons
÷2/4
I Q
fLO
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Dual-Conversion Transmitters
fLO2IfLO2Q
fLO1
• No pulling
• LOFT/IR less problematic
• Sliding IF
• Higher power
• More complex filtering needed
Pros Cons
÷N
13 Zargari, JSSC 2002
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Third Harmonic Folding
fLO 3fLO
A
fLO +f1 fLO +f2
A/3
3fLO -f13fLO –f2
f
a3vd 3(t)
f
9a3A 3/43a3A 3/4
3a3vd 2(t)vu(t)
fa3A 3/4
a3A 3/2
fLO +2f1-f2 fLO +2f2-f1
fLO -2f1-f2fLO -2f2-f1
3a3vd (t)vu2(t)
f
a3A 3/2a3A 3/6
fLO +2f1-f2 fLO +2f2-f1
PA driver nonlinearity: y=a1x+a3x3
un
des
ired
co
mp
on
ents
vd (t) vu (t)
f LO
-3
f 1
…
…
…
23 Mirzaei, TCAS 2011
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• -160dBc/Hz RX-band noise
results in 0.5dB NF degradation
RF IC
RX Desired
TX Leakage
WCDMA TX General Requirements
• ACLR1 at 5MHz: -33dBc
• ACLR2 at 10MHz: -43dBc
• EVM: 19%
Noise Floor = 28-50-160 = -182dBm/Hz
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• In linear TX, IQ imbalance, LOFT & PN dominate
WCDMA TX EVM
101010 101010(%)
PNLOFTIQ
EVM ++=
• 40dBc equal contribuXon results in √3 = 1.7% EVM
• Baseband filter ripple adds further
• Typical RF IC EVM around 3%
1
Error+1.9
Mf L
O
-1.9
MNoise Floor
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• Nonlinearity results in ACLR
– Depends on PAR, modulation
WCDMA TX ACLR
+1.9
M
0
-1.9
M
5±1.92MHz
ACLR1, dBc
IM3
• ACLR1 requirement of -33dBc at the antenna
– PA WC -37dBc (optimized for efficiency)
–2dB production margin
–Leaves RFIC WC of -40dBc
+3dBm
0d
Bm
-31
dB
c
OIP
3=
15
.5d
Bm
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Folding Impact on PAD Linearity
• With third harmonic present: ACLR = -38 dBc
• With third harmonic removed: ACLR = -44 dBc
• Makes the PAD linearity requirements more stringent
DAC
DAC
f
1
≅≅≅≅ 1/3 ≅≅≅≅ 1/5
vRF,1(ωωωω)
vRF,5(ωωωω)vRF,3(ωωωω)
fLO 3fLO 5fLO
PAD
-6 -4 -2 0 2 4 6
-80
-60
-40
-20
Output 3G Signal
Frequency, MHz
Po
we
r, d
Bc
PAD Ideal
w/ 3rd
w/o 3rd
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Case Study: Direct-Conversion 3G TX
• Passive 25% mixer
• LOFT scales w/ RF gain
I
…
10-20dB> 70dB
+24
~ -
50
dB
m
Q
GC
PAD Units
1
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GSM RX-Band Noise Requirements
TX noise in RX-band -79dBm not to mask adjacent RX
Corresponds to a 20MHz phase noise of:
88
0
91
5
93
5
96
0
EGSM TX
+33dBm
-79dBm
Typical PA noise ≈ -83dBm, leaving -165dBc for RF IC
-112dBc spur, five exceptions allowed
EGSM RX
≈≈ ≈≈ ≈≈ ≈≈
Freq, MHz20M
PN = -79dBm – 10Log(100kHz) – 33dBm = -162dBc/Hz
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Linear TX vs. Translational Loop
PFD/CP
LoopFilter
fLO
fLO+fIF
Modulator fIF
• Sensitive to Pulling
• 20M noise an issue
• Simple
• Generic TX
• No pulling issue
• Relaxed filtering
• More complex
• Suitable for PM only
2 Erdogan, ISSCC 2005
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MMD
PFD/CP
∆Σ∆Σ∆Σ∆ΣModulator/
Pre-distortion
Reference
• Mixer/LO, analog modulator eliminated
• More sensitive to analog impairments
• Trade-off between BW and phase noise
PLL-Based Transmitters
3 Bonnaud, ISSCC 2006
Lowpass100kHz/
40
0kH
zPLL
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GSM Mask & Phase Error Calculations
• -60dBc at 400kHz
– 3dB production margin
– 2dB PVT margin
• 5⁰ RMS phase error
– 2⁰ production margin
– 2⁰ PVT, BW1
00
kHz-88dBc
-88 + 10Log(200kHz) = -35dBc = 1⁰
Frequency
PN
Power integrated in 30kHz BW≈ 10Log (200k/30k)
PN = -65 – 10Log(30kHz) – 9 = -118.8dBc/Hz
0.0178 Radian
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MMD
PFD/CP
∆Σ∆Σ∆Σ∆Σ
Mo
du
lato
r
Reference
PM
AM
A(t)
Sin(ωωωω0t+φφφφ(t))
∆Σ∆Σ∆Σ∆Σ
A(t)Sin(ωωωω0t+φφφφ(t))
• Lower power consumption
• Compatible with GMSK TX
• Very sensitive to nonlinearities
Basics of Polar Transmitters
I + jQ = rejθθθθ
EDGE Constellation
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-20
-60
-40
-80
0
-40
0
-80
0
40
0
80
0
Frequency, kHz
Am
pli
tud
e, d
B
PMAM
8PSK
EDGE AM & PM Signals Spectrum
Ideal20nS40nS80nS160nS
0
-40
0
-80
0
40
0
80
0
Frequency, kHz
• AM & PM stand-alone signals much wider
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MMD
PFD/CP
∆Σ∆Σ∆Σ∆Σ
REF
PM
• Phase noise
• VCO & CP nonlinearity due to large swing, wide BW
• PLL BW needs to be accurately controlled
BW ∝∝∝∝ KVCO × R × ICP : Measure KVCO and adjust ICP
PM Path Concerns
200 300 400
-40
-20
0
20
40
Time, µµµµS
VC
TRL
Swin
g, m
V
5,9 Darabi, JSSC 2011
Sin(ωωωω0t+φφφφ(t))
φφφφ/KVCO
Only function of KVCO
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-70
-65
-60
-55
-50
-30
-15 0
15
30
45
AM-PM Relative Delay, nS
±40
0kH
z M
od
, dB
c
Corrected
AM-PM Uncorrected
AM Path Concerns
• AM-AM/PM distortion in PAD
• Phase feed-through
Mask Limiting Factors:
AM
Static: AM-AMDynamic: AM-PM
PA or PAD
40
0kH
z
20
dB
/
200kHz/
PFT
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MMD
PFD/CP
∆Σ∆Σ∆Σ∆Σ
Mo
du
lato
r
REF
PM
AM∆Σ∆Σ∆Σ∆Σ
• HP path to give a flat response
• Accurate KVCO needed
• Accurate AM-PM matching needed
2-Point PLL Based Polar Transmitters
+
10 20 30 40 50
-80
-40
0
Frequency, MHz
Mag
nit
ud
e, d
Bc
AM
PM
3G
3G AM & PM Signals
LP
HP
×1
/KV
CO
KVCO
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• KVCO = dωωωω/dV = 0.5×ωωωω00003×L× (dCVAR/dV)
Impact of VCO Nonlinearity on 3G SignalEV
M, %
-0.8
-0.4
0 0.4
0.8
VCO Gain Error, %
0.5
1.0
1.5
• KVCO accuracy/linearity of better than 2% needed
• LC and CVAR not modeled accurately
AC
LR, d
Bc
1 2 3 4 5
VCO Nonlinearity, %
-60
-50
-40
ACLR2
ACLR1
PVT Dependent
PLL BW: 250kHz
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Case Study: 3G Polar TX
• < -40dBc ACLR, < 3% EVM
6 Youssef, JSSC 2011
MMD
PFD/CP
Mo
du
lato
r
REF
PM
AM
∆Σ∆Σ∆Σ∆Σ
+ ÷2
÷4
÷2
÷2
F/V OUT
LB
HB
HP Path
Matched20M10b
Linear VCO
∆∆∆∆T
PLL (250kHz)
AM Path
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Summary & Conclusions• Standards set design parameters, radio architecture
• On receiver side:
Architecture 1/f, IIP2 IMR Linearity Limitations
Zero-IF Poor Self Modest WB
Low-IF Modest In-band Modest NB
• CM receivers improve linearity, relax filtering
• On transmitter side:
Architecture Power Noise Pulling Limitations
Direct Modest Poor Poor Generic
PLL Lowest Good None Only PM, NB
Polar Lowest Good Good Complex, NB
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