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Simplified Transceiver Architecture. HPMX-2007. The lkhefw wlkhq wilehr. The lkhefw wlkhq wilehr. The lkhefw wlkhq wilehr. wejklh wajkhrqwilu wae. wejklh wajkhrqwilu wae. wejklh wajkhrqwilu wae. esjlkh qwh wlh lihewrw. esjlkh qwh wlh lihewrw. esjlkh qwh wlh lihewrw. - PowerPoint PPT Presentation
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Simplified Transceiver Architecture
Role of a Transmitter
090
AD
AD
HPMX-2007
The lkhefw wlkhq wilehrwejklh wajkhrqwilu wae.esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih qwejklh wajkhrqwilu wae.esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih qwejklh wajkhrqwilu wae.esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih qwejklh wajkhrqwilu wae.esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q
wklhjr qlih qilh q q3wih qwejklh wajkhrqwilu wae.esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih qwejklh wajkhrqwilu wae.esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q
The lkhefw wlkhq wilehrwejklh wajkhrqwilu wae.esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih qwejklh wajkhrqwilu wae.esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih qwejklh wajkhrqwilu wae.esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih qwejklh wajkhrqwilu wae.esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q
wklhjr qlih qilh q q3wih qwejklh wajkhrqwilu wae.esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih qwejklh wajkhrqwilu wae.esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih qwklhjr qlih qilh q q3wih qwejklh wajkhrqwilu wae.esjlkh qwh wlh lihewrw
The lkhefw wlkhq wilehrwejklh wajkhrqwilu wae.esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih qwejklh wajkhrqwilu wae.esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih qwejklh wajkhrqwilu wae.esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q
wklhjr qlih qilh q q3wih qwejklh wajkhrqwilu wae.esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih qwejklh wajkhrqwilu wae.esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih qwklhjr qlih qilh q q3wih qwejklh wajkhrqwilu wae.esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih qwejklh wajkhrqwilu wae.
Power Supply
Power Amplifier
Mixer
Oscillator
Baseband Processor
Modulator
bias
I Data
Q Data
1. create carrier
2. add data to carrier
4. amplify to broadcast
3. shift to high frequency
Information
Antenna
bias
uP/DSP
Transceiver
Role of a Receiver
090
AD
AD
HPMX-2007
The lkhefw wlkhq wilehrwejklh wajkhrqwilu wae.esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih qwejklh wajkhrqwilu wae.esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih qwejklh wajkhrqwilu wae.esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih qwejklh wajkhrqwilu wae.esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q
wklhjr qlih qilh q q3wih qwejklh wajkhrqwilu wae.esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih qwejklh wajkhrqwilu wae.esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q
The lkhefw wlkhq wilehrwejklh wajkhrqwilu wae.esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih qwejklh wajkhrqwilu wae.esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih qwejklh wajkhrqwilu wae.esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih qwejklh wajkhrqwilu wae.esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q
wklhjr qlih qilh q q3wih qwejklh wajkhrqwilu wae.esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih qwejklh wajkhrqwilu wae.esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih qwklhjr qlih qilh q q3wih qwejklh wajkhrqwilu wae.esjlkh qwh wlh lihewrw
The lkhefw wlkhq wilehrwejklh wajkhrqwilu wae.esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih qwejklh wajkhrqwilu wae.esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih qwejklh wajkhrqwilu wae.esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q
wklhjr qlih qilh q q3wih qwejklh wajkhrqwilu wae.esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih qwejklh wajkhrqwilu wae.esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih qwklhjr qlih qilh q q3wih qwejklh wajkhrqwilu wae.esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih qwejklh wajkhrqwilu wae.
Power Supply
uP/DSP
Low Noise Amplifier
Mixer
Oscillator
Baseband Processor
De-Modulator
bias
I Data
Q Data
1. amplify received signal with min. added noise
2. shift to lower frequency (cost and/or performance)
3. LO for down conversion
4. discard carrier and recover data
Information
bias bias
Antenna
Mixer = Multiplying up/down conversion
• Frequency translation device
• Ideal mixer:
– Doesn’t “mix”; it multiplies
A
B
AB
Image problem converting to IF
A1cos(wRFt)
A has desired signal at IF
plus an interference at IM
A2cos(wIMt)
B is at LO
And:
RF - LO = LO - IM = IF
Both converted to IF,Can’t be cleaned once corrupted
Image Problem
Problem of Image Signal
IF
RFimage LO
Problem of Image Signal
• Solution: Image Rejection Filter
Problem of Half IF
• Second order harmonic
0
Superheterodyne Receiver
Multi IF Stage Receivers• Received RF signal is down converted stage by
stage until the desired final IF is obtained• Frequency conversion ratio of each stage is
usually kept lower than 10. – For example, RF 1800 MHz IF1 450 MHz, then
IF2 90 MHz, and finally IF3 18 MHz.– Corresponding ratios are: 4; 5; 5; total 100.
• Each stage has it’s own image problem• Each stage requires demanding filtering
– Typically done off chip or using SAW– Complicated, bulky, expensive
IF and LO frequency selection• Fixed RF filter before LNA for band selection
– One for each standard– Off-chip, high quality, no freedom
• IF frequency is selected at design– Fixed for each product
• LO frequency is tuned in real time– |RF–LO|=IF– Actual RF freq depends on which channel is
assigned to device– LO tuning range must cover RF bandwidth
Superheterodyne Receiver(cont.)
Selection of IF
• If IF is large, – better separation between RF and image– better image rejection– easier image rejection filter design– More stages of down conversion
• Other IF selection criteria– Select IF so that image freq is outside of RF
band IF >= (RF BW)/2
• Sometime may not be possible, if (RF BW)/2 is within RF Band
• For each channel assignment, there are two choices of LO freq that meets the requirement |RF–LO|=IF.
• Q: should LO > RF, or LO < RF??
Example: AM Radio• AM radio band: 530 to 1610 KHz• BW/2 = (1610-530)/2=1080/2=540, in band• IF has to be lower. Commonly: 455kHz• Image can be in AM band• If LO is on low side, LO tuning range is:
– (530 to 1610) – 455 = (75 to 1155)– LO lowest to highest is a factor of 15.4
• If LO is on high side, LO tuning range is:– (530 to 1610) + 455 = (985 to 2065)– LO lowest to highest is a factor of 2.01
Direct Conversion Receiver
No image problem
PGA
PGA
LNA
RFSAW ADC
ADC
DIG
ITA
LF
ILT
ER
I
Q
RFPLL
sin cos
270 kS/s
925-960MHz
925 - 960MHz
Direct Conversion Receiver
LO is at same frequency as RF1/f noise here can end up in channelSelf mixing cause DC problem
+ Eliminate IF SAW, IF PLL and image filtering+ Integration+ Avoids image problem
- Quadrature RF down conversion required- DC problem- Typically requires offset or 2x LO to avoid coupling
DC Offset (Self-mixing)
ADc
aLO(t)=ALOcos(c+)
0
ADc 0
c
c
)(, tx LOoffset
)(, tx RFoffset
capacitive couplingsubstrate couplingbondwire coupling
capacitive couplingsubstrate couplingbondwire coupling
Saturates the following stagesSaturates the following stages
DC Offset (Self-mixing)
θωω
θωθωω
ω
tAA
tAtAA
tataAtx
cLOcrosstalk
cLOcLOcrosstalk
LOLOcrosstalkLOoffset
2cos1)(
coscos)(
)()()()(
221
,
φωω
φωω
ω
)(2cos1)(
)(cos)(
)()()()(
2interferer2
1
22interferer
interfererinterfererinterferer,
tmtAA
tmtAA
tataAtx
ccrosstalk
ccrosstalk
crosstalkoffset
level
DC Offset
+
-
t
DC Offset Cancellation
• Capacitive Coupling– Requires a large capacitor
• Negative Feedback– Nonlinear
• TDMA Offset Cancellation– Requires a large capacitor
-A
1/f noise effect
• CMOS transistors has significant 1/f noise at low to DC frequency
• Significantly noise performance of direct conversion receivers
Receive signal1/f noise
f
Even-Order Distortion
0
0
Direct feed through
Direct feed through
Mirror Signal
• Upper sideband and lower sideband are identical
RF
LO
0
0
Mirror Signal • Upper sideband and lower sideband are not
identical
RF
LO
0
0
Mirror Signal Suppression
AD
090
AD
a(t)
ui(t)
uq(t)
vi(t)
vq(t)
• Quadrature Down Conversion
I
Q
Quadrature Conversion
)(
)(tan)(
))(tan()(
)(
))(sin()(
))(cos()(
)sin()()(
)cos()()(
))(cos()(
1
21
21
tv
tvtm
tmtv
tv
tmtv
tmtv
ttatu
ttatu
tmtta
i
q
i
q
q
i
LOq
LOi
RF
Quadrature Down Conversion
0
0
I/Q Mismatch
090
I
Q
Phase & Gain Error
Phase & Gain Error
Phase & Gain Error
a(t)
I/Q Mismatch due to LO errors
2)(sin
21
2)(
2)(cos
21
2)(
2sin
21)(
2cos
21)(
)(cos)(
,
,
,
,
tmA
tx
tmA
tx
ttx
ttx
tmtAta
QBB
IBB
cQLO
cILO
c
2
2ˆ
ˆ
2222
1
)(
)()(ˆ Find :Exercise
unbiased. is )(ˆ Hence,
)())(ˆ( Clearly,
0)(,))((,))(( and
0)( ,0)( Suppose
)2/)(cos()2/1(
)2/)(sin()2/1(tan)(ˆ
tm
tmtmEσ
tm
tmtmE
EσEσE
EE
tm
tmtm
def
m
m
ε
Phase errorPhase errorGain errorGain error
Effect of gain mismatch Effect of phase mismatch
Use of I/Q down conversion recovers the nonsymmetrical receive signal spectrumBut port isolation becomes more challengingSelfmixing and even order distortion may affect both channels and affect each other, causing additional I/Q mismatch
090
a(t)
A/D
A/D
Base Band
DSP
Phase and gain mismatchcompensation
DC and 1/fcancellation
Summary of Direct Conversion Receiver
• No need for imager reject filter• Suitable for monolithic integration with baseband • DC offsets due to crosstalk of input ports of
mixer• Even order IM direct feed through to baseband• Quadrature down conversion suppresses mirror• I/Q mismatch due to mismatches in parasitics• Low power consumption attributes to less
hardware
ADC
ADC
PGA
PGA
LNA
RFPLL
DIG
ITA
LF
ILT
ER
100 kHz
I
Q
sin cos
RFSAW
sin cos
270 kS/s
925-960MHz
925.1 - 960.1MHz
Low IF receiver
- Quadrature RF down conversion required- Require higher performance ADC-Additional mixer-Slower RF PLL settling-Even order distortion still problem-Low freq IF filters require large chip area
+ Eliminate IF SAW, IF PLL and image filtering
+ Integration
+ Relaxes image rejection requirements
+ Avoids DC problems, relaxes 1/f noise problem
Low-IF Down Conversion
Complex BPF
Mirror signal, needs removal
Mirror Signal Suppression (1)
ComplexBandpass
Filter
I Q I Q
LO1 LO2
Mirror Signal Suppression (2)
I Q I Q
LO1 LO2
Both schemes used in heterodyne receivers for image rejectionMathematical analysis very similar
Image rejection architectures
• Use additional hardware (LO’s, mixers, and filters)
• Use I/Q channels which process + or – frequencies differently
• Two steps of I/Q to solve both image and mirror problems
• Effects limited by I/Q channel/filter matching accuracies
Image Reject Receiver
• Hartley Architecture
-90°
090
RFinput
IFoutput
A
B
C
LO
tLOωsin
tLOωcos
Hartley Architecture
LOLO LO0
)(BX 0
0
2/j
2/j
0)(AX
90 0
0
0
xcos
xsin
IQ error effect
• Ideal IQ: image completely rejected
• If signal and image not single tone, 90o shift is not exact
• Local oscillator’s sine and cosine not matched in magnitude and phase
• 90o phase shifter may have both gain and phase error
• All lead to incomplete image rejection
IPR Evaluation and IRR – LO error
tAA
tAA
tx imLOimLO
RFLORFLO
A )sin(2
)sin(2
)(
)(cos2
)()(cos2
)()( tA
AtA
Atx imLOim
LORFLORF
LOB
)cos(2
)cos(2
)(
t
At
AAtx imLO
imRFLO
RFLOC
cos2
cos2
)()( t
AAt
AAtx RFLO
RFLORFLO
RFLOsig
cos2
cos2
)()( t
AAt
AAtx imLO
imLOimLO
imLOim
cos)(2)(
cos)(2)(.
22
22
2
2
LOLOLOLO
LOLOLOLO
RF
im
outsig
im
AAAA
AAAA
A
A
P
P
Input image power ratio
44
4
4
)cos1)((2
cos)(2)(
cos)(2)(
22
22
2
222
2
2
22
22
AA
AIRR
A
A
A
AA
AAAA
AAAAIRR
LO
LO
LO
LOLO
LOLOLOLO
LOLOLOLO
Image Reject ReceiverHartley Architecture with simple 90 deg phase shiftor
1
1
1
1222222
CRCCRR
CCRR
A
A
2
1
2
C
C
R
RC
CR
RC
CR
R
A
A
Gain Mismatch due to R, C errors
At w = 1/RC:
Weaver Architecture
1LOω 1LOω0
0
0
0
)(CX
)(DX
0
2/j
2/j
0)(AX
2/j
2/j
02LOω2LOω
0
)(BX2/1 2/1
00
2LOω 2LOω
Weaver Architecture
1LOω
1LOω0
0
0
0
)(CX
)(DX
0
2/j
2/j
0)(AX
2/j
2/j
02LOω2LOω
0
)(BX2/1 2/1
00
2LOω 2LOω
RFLOLO ω2ω2ω 21
RFLOLO ω2ωω 21
1ωω LORF 21 ωωω LOLORF
Digital IF?• To avoid 0-IF or low-IF issues, IF frequencies
can’t be too low• Recall: RF-IF ratio within 10• Typical RF freq is in 1 to 5 GHz, IF needs
to be more than 100 to 500 MHz• But dynamic range requirements requires >=
14 bit resolution• No such ADC’s are available
• But signal bandwidth much smaller,• Subsampling Receivers
• Example: 1.8 GHz GSM Specifications: IF carrier frequency = 246 MHz, Channel BW = 200 KHz, Input Dynamic Range = 90 dB.
2 digital low frequency mixers, no noise and distortion. Easier I&Q matching. No DC offset and 1/f noise. More digital means easier integration on a CMOS process.x SNR degradation due to noise foldingx ADC & SH have to run at high clock to minimize noise folding.
Noise folding problem
IF
White noise
0
… …
fs 2fs
IF0
… …
Baseband noise increased by IF/fs factor
• The aliased noise, once happened, cannot be removed in the digital domain
• Band pass filtering of IF before sampling can reduce the noise in lower frequency– Requires expensive IF filters– Against the spirit of moving more things to
digital
• Reduce IF frequency and increase fs frequency so that IF/fs ratio is not large– More stringent requirement on RF filtering and
image rejection– Requires faster ADC
ExampleUMTS/DCS1800 Specifications
Frequency BandChannel BWSystem SensitivityBER
BlockingCharacteristics
Adjacent ChannelInterference
DCS18001805 - 1880 MHz200 kHz-102 dBm1e-3600 - 800 kHz: -43 dBm800 - 1600 kHz: -43 dBm1600 - 3000 kHz: -33 dBm> 3000 kHz: -26 dBmCochannel: -9 dBc200 kHz: 9 dBc400 kHz: 41 dBc600 kHz: 49 dBc
UMTS2110 - 2170 MHz5 MHz-117 dBm(@32ksps)1e-310 - 15 MHz: -56 dBm15 - 60 MHz: -44 dBm60 - 85 MHz: -30 dBm> 85 MHz: -15 dBm
5 MHz: -52 dBm
Sensitivity
• Adjacent Channel Interference
• Co-Channel Interference
Desired Channel
Adjacent Channel
Adjacent Channel
MHz890.4 890.4 890.6
890.4
890.4 890.4
890.4890.4
890.4 890.4
Multi-Channel, Multi-Mode DynamicRange, DCS1800
Multi-Channel, Multi-Mode DynamicRange, DCS1800
PB = 13 dBm, Px = -60 dBm
PB:Px = 73 dB
If want FS:1LSB > 73 dB >12 bit resolution
If want digital channel selection + filtering, fs >= 2BW fs >= 150MHz
If want noise floor 20 dB below wanted signal SFDR >= 13 – (-60) + 20 = 93 dB
Type of ADC needed: 150 MSPS, 13-14 bit, 95-100 dB SFDR
Sensitivity
Receiver Thermal Noise
Receiver Added Noise
Desired Signal
(dB)(dBm)
(dB)(dB)(dBm)(dBm)
min
minmin,
SNRP
SNRFkTBPSensitvity
nf
receiverin
(dB)(dBm)(dBm) receivernf FkTBPFloorNoise
Sensitivity
ERP = +50 dBm
Power to Antenna: +40 dBm
TX. Antenna Gain: +10 dB
Frequency: 10 GHz
Bandwidth: 100MHz
Rcvr. Antenna Gain: +60 dB
Transmitter:
ERP
Path LossesRcvr. Ant. Gain
Power to Receiver
Receiver:
Noise Floor @ 290KNoise in 100 MHz BWReceiver N.F.
Receiver Sensitivity
Margin: 4 dB
+ 50 dBm-200 dB
60 dB
-80 dBm
- 174 dBm/Hz+ 80 dB+10 dB
-84 dBm
How to increase Margin by 3dB ?
Path Losses: 200 dB
Selectivity
Ch1
Ch2
Chn
Ch3
RF Filter
freqfRF
Ch1
Ch2
Chn
Ch3
freqfIF
IF Filter
freqfLO
Selectivity
RF Filter
IF Filter
• IF filter rejection at the adjacent channel
• LO spurious in IF bandwidth
• Phase noise of LO
Receiver Added Noise
Receiver Thermal Noise
Noise Figure Calculation
receiver
BasebandRF input
nfP
minSNR
NFinSNR
Standard Bandwidth10log(BW) Sensitivity(dBm) Noise Floor (dBm) SNRin(dB) NF(dB) SNRmin(dB)
DECT 1.70E+06 62.30 -83.00 -111.50 28.50 18.20 10.3
GSM 2.00E+05 53.01 -102.00 -120.79 18.79 9.79 9
WLAN 2.00E+06 63.01 -80.00 -110.79 30.79 15.69 15.1
BW
RdB
NE
dBSNRBW
R
NE
SNR symbolssymbols log10)()(0
min0
min
17!17!
Es/No or Eb/No=?
IP3 Calculation
10
23
3)(2
31
min3
min3
IIPdB
nfsfIIP
nfIIPsf
PP
PSNRDRP
SNRPP
DR
Standard DR SFDR IIP3 Pmax Bandwidth 10log(BW) Sensitivity(dBm)Bluetooth 50.00 36.57 -10.00 -20.00 1.00E+06 60.00 -70.00GSM 87.00 61.67 -5.00 -15.00 2.00E+05 53.01 -102.00WLAN 76.00 52.30 6.00 -4.00 2.00E+06 63.01 -80.00
Image Rejection Calculation
SNRmin
fIF
IRrequired
fRFfLO
Pdesired
PImage
minSNRPPIR desiredimagerequired
(all in dB’s)
Transmitter Architecture
• Direct Conversion Transmitter
• Two-step Conversion Transmitter
• Offset PLL Transmitter
Transmit Specifications• Transmit spectrum mask
Receiver Specifications
20 20
4040
Adjacent channel
alternate adjacent channel
Direct-conversion transmitter
090
I
QLO
Pros: less spurious synthesizedCons: more LO pulling
• Direct-conversion transmitter with offset LO
090
I
Q
LO1
2
Pros: less LO pullingCons: more spurious synthesized
• Two-step transmitter
090
I
Q
cos1tcos2t
12
Pros: less LO pulling superior IQ matchingCons: required high-Q bandpass filter
• Offset PLL transmitter
090
I
Q
cos1tPD/LPF VCO
1/N
Weaver Architecture
Wideband IF Architecture