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J.Dąbrowski, RF TRx Design1
Radio Frequency Transceiver Design
Jerzy DąbrowskiDivision of Electronic Devices
Department of Electrical Engineering (ISY)Linköping University
e-mail: [email protected]
http://www.ek.isy.liu.se/courses/tsek04/
J.Dąbrowski, RF TRx Design2
Objectives of the course
• Understand the contemporary wireless communication standards at the physical layer
• Strengthen the knowledge of RF transceiver architectures
• Learn design methods and techniques for RF front-end design at the system level
• Get familiar with professional design tools
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J.Dąbrowski, RF TRx Design3
Organization of the course
• Lectures 10 x 2h• Laboratory work 4 x 4h
(by Jonas Fritzin and Amin Ojani) Lab Manual by Jonas Fritzin
• Project work: RF transceiver design- Part 1. Synthesis by analytical model - Part 2. Simulation and verification by ADS
• Course book: Qizheng Gu, RF System Design of Transceivers for Wireless Communication, Springer 2005
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Outline of the lecture
• Wireless communication systems today
• RF transceiver architecture
• Architectures- receiver- transmitter
• Summary
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J.Dąbrowski, RF TRx Design5
Wireless Communication Systems Today
WLANBluetooth
DECTPHS
CT1/CT2
GSMIS-54/IS-95
PDCGPS
Satellite
Paging
10m 100m 1000m 10km 100km 1000km Range
Bit Ratekb/sec
1
10
100
1000
In-door
Cordless
Cellular
3G directions
UMTS CDMA2000
Zigbee
10,000
UWB100,000
4G directions
LTE/WiMax
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Wireless Communication Systems Today (cont’d)
WLAN802.11b/g
DECTDCS-1800PCS-1900
1 2 3 4 5 6 GHz
Power(mobile)
1mW
10mW
100mW
1W
UMTS CDMA2000
Zigbee
10W
UWB
Frequency
Bluetooth
GSMWLAN802.11aWiMax
802.16e
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Overview of Standards
1 W1, 2, 11Mb/s
QPSK/CCK25 ppm20 MHz2400-2483CDMA/TDD802.11b(DSSS)
0.125, 0.25, 0.5, 2W
3840 (max)
QPSK, 16/64QAM
0.1 ppm5 MHz1920-1980 (UL)2110-2170 (DL)
W-CDMA/ TD-CDMA/F/TDD
WCDMA(UMTS)
1,4,100 mW1000GFSK20 ppm1 MHz2400-2483FHSS/TDDBluetooth
Peak PowerRate(kb/s)
Modulation Technique
FrequencyAccuracy
ChannelSpacing
Frequencyband (MHz)
Access Scheme/Dupl
Standard
N/A
0.8, 1, 2, 3 W
250 mW
0.8, 2, 5, 8 W
0.8, 2, 5, 8 W
1228
48
1152
270.8
270.8
GMSK90 Hz200 kHz1710-1785 (UL)1805-1850 (DL)
TDMA/FDMA/ TDD
DCS-1800
OQPSK
π/4 QPSK
GMSK
GMSK
N/A1250 kHz
824-849 (RL) 869-894 (FL)
CDMA/ FDMA/FDD
IS-95cdmaOne
200 Hz30 kHz824-849 (RL) 869-894 (FL)
TDMA/FDMA/FDD
IS-136D-AMPS
50 Hz1728 kHz1880-1900TDMA/FDMA/ TDD
DECT
90 Hz200 kHz890-915 (UL)935-960 (DL)
TDMA/FDMA/ TDD
GSM
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RF Transceiver at glance
RxFrontend
DigitalBaseband
• RF frontend – analog, high frequencies
• Baseband - digital today (DSP), low frequencies
• Mostly common antenna – duplexer/switch( full/half duplex )
Duplexeror switch
TxFrontend
ADC
DAC
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Today’s communication radio
Cellular handsets use many modules to maintain different functions and operation modes
RF front-endAnalog BBDigital BB Power managementI/O’sPeripherals
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Digital Transmitter
Upconverter/Modulator
Carrier
Modulation & DSPADC
Basebandsignal
Digital baseband section (compression, coding,
modulation, shaping ) RF section (up-conversion, filtering, power gain and control)
DAC
Tradeoff between power efficiency and spectral efficiency
RFFilterPA
Power control
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Digital Receiver
Carrier
DownConverter ADC
Basebandsignal
Digital baseband section (equalization, demodulation, decoding, decompression)
RF frontend(image rejection, low noise, gain control, down conversion, channel selection)
RFFilter
Demodulator & DSP
LNA IF/BBFilter
Gain control
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Basic receiver and transmitter architectures
• Superheterodyne Receiver• Homodyne (Zero-IF Receiver)• Low-IF Receiver
• One-step Transmitter• Two-step Transmitter• Offset-frequency Transmitter
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Superheterodyne receiver• Double conversion - tradeoffs mitigated
(good sensitivity and selectivity, good image rejection)
IR Filter
RFFilter
LO1
IF Filter
LNA IFA
LO2
I Q
LP Filter ADC
• Discrete IR and IF filters not amenable for integration
• Low impedance of those filters raise power dissipation in LNA and first mixer (matching for off-chip needed)
Gain control
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Superheterodyne receiver (cont’d)
fk f
RF filter selects band, rejects off-band signals,
IR filter rejects off-band products, it has same band as RF filterfLO,k
Receiver band Bw
fk-1fLO,k-1
Constant intermediate frequency fIF
fIF
LO1 frequency is adjusted to select the channel for down-conversion
fIF f
IF filter selects channel,adjacent channels are partly suppressed
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Homodyne receiver (Zero-IF)• – Direct conversion
(fewer components, image filtering avoided – no IR and IF filters)
RFFilter
LNA
LO
I Q
DC removal+ LPF ADC
• Large DC offset can corrupt weak signal or saturate LNA (LO mixes itself), notch filters or adaptive DC offset cancellation – eg. by DSP baseband control
• Flicker noise (1/f) can be difficult to distinguish from signal
• Channel selection with LPF, easy to integrate, (noise-linearity-power tradeoff are critical, even-order distortions low-freq. beat – differential circuits useful)
LO Leakage fLO = fRF fIF = 0
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Homodyne receiver (cont’d)
fk f
RF filter selects band, rejects off-band signals,
Receiver band Bw
fk-1
fLO,k = fk
Wanted channel is corrupted by its mirror,IQ downconversion is needed to separate them with Hilbert transform
fIF = 0 f
fIF = 0 f
LP filter selects channel, It is also anti-alias filter for ADC
Useful for wideband systems, DC and 1/f noise can be removed by HPF
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Low-IF receiver• Tradeoff between heterodyne and homodyne
RFFilter
LNA
LO
I Q
Polyphasefilter ADC
LO Leakage
• DC offset and 1/f do not corrupt the signal, like in the superheterodyne, still DC offset must be removed /saturation threat
• But image problem reintroduced / close image !
• Still even-order distortions can result in low-freq. beat – differential circuits useful
supports IQ rejection
Amp
Gain control
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Low-IF receiver (cont’d)
fk f
fLO,k
fIF fIF
Desired channel
In-band image channelRF band
filter
Close-image problemImage and desired channel signal overlapat fIF frequency, but due to I and Q paths and Hilbert transform the image can be suppressed
More severe problem than in zero-IF since theimage can be much stronger than the signal.
Tough requirements for IQ match if image is large, otherwise signal strongly corrupted
Good for GSM std. since the adjacent channel only 9dB larger, so rejection of 20..30 dB enough
fIF = ½ BWch typical
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IQ downconversion in Zero-IF
-ω0 ω00
Inherent mirror spectrum
-ω0 ω00Aliasing by mirror
IQ mirror cancellation after using Hilbert transform
0
Down conversion to zero with one mixer
-ω0 ω00
Down conversion to zero with quadrature IQ mixer
and
0
)ω()ω()sgn(
2ILP
j
QLP YeY ±⋅− ωπ
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IQ downconversion in Zero-IF (cont’d)
sIQ (t) = A(t)cos(ω0t + ϕ(t)) = aI (t)cosω0t - aQ (t)sinω0t
For any modulation scheme:
LPF
sinω0t cosω0t
sIQ (t)
LPF
aI (t)
-aQ (t)
BB signal decodedas I and Q component,but can be degradedby IQ mismatch (cross-talk)
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J.Dąbrowski, RF TRx Design21
IQ downconversion in Low-IF
-ω0 ω00
Inherent mirror spectrum
-ω0 ω00Aliasing by image
IQ image cancellation after using Hilbert transform
0
Down conversion with one mixer
-ω0 ω00
Down conversion with quadrature IQ mixer
and
0
)ω()ω()sgn(
2ILP
j
QLP YeY ±⋅− ωπ
J.Dąbrowski, RF TRx Design22
Direct conversion transmitter
MatchingNetworkPA
Duplexer
or Switch
Receiver
Asinωct Acosωct
LO
I
Q
Bas
e ba
nd
BPF
Leakage of PA
• Up-conversion is performed in one step, fLO= fc
• Simple modulation, e.g. QPSK can be done in the same process
• BPF suppresses harmonics
• LO must be shielded to reduce corruption
• I and Q paths must be symmetrical and LO in quadrature, otherwise crosstalk
High-power signal
FDD or TDD,respectively
Leakage of LO
Also effect on Rx can be critical
Power control
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Two-step transmitter
PA
cosω1t
BPF1
sinω1t
cosω2t
BPF2
IF frequency
Suppresses harmonics of ω1
Removes sideband at ω1- ω2 but must have high Q-factor up to 60dB as 2nd modulator outputs equal sidebands
Advantage:
Better IQ matching since ω1 is lower
Carrier far from LO’s frequency
ω1+ ω2
I
QPower control
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Two-step transmitter (cont’d)
PA
cosω2tsinω2t
BPF
SSB generation with quadrature scheme
BPF helps to remove sideband at (ω1-ω2) due to mismatch, but requirements for Q relaxed
ω1+ ω2
cosω1t sinω1t
ttttt )cos(sinsincoscos 212121 ωωωωωω +=⋅−⋅
LPF
LPFPower control
I
Q
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Offset-PLL transmitter
cosω0t
I
QPFD
sinω0tPA
LPF
900
RefLO
VCO
LO
BPF
Offset mixer
BPF
fref = fVCO - fLO
• The PLL loop forces the IQ mixers to minimize their wideband noise mainly introduced by BB signals.
• Mainly the VCO contributes noise at the RF output.
• Pulling of LO is avoided
Low noise at output
Power control
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Problem of carrier leakage
PABPF
Leakage of LO
Asinωct
Acosωct
I
Q
Calibrationfeedbackto BB
fRF
Wantedtransmitted signal
Carrier fallsin band
Constellation are destroyed by offset and also EVM rises
Tx measures output when BB signal is absent and introduces offset in BB stage to compensate for the carrier leakage
aI (t) → aI (t) + ΔIaQ (t) → aQ (t) + ΔQ
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Multi-standard flexible Tx
AmplitudePhase
PFD PA
Ref LO
VCO
Multi Moddivider
d/dtDAC
• AM and PM separated(EER technique)
• High efficiency PA with feedback
• RF Filters eliminated
DAC
LPF
AM
Envelopedetector
LoopFilter
LPF
ΣΔModulator
Feedbackreduces IMD (Amp-Phase imbalance)
φin(t)Ain(t)
Ain(t )cos(ω0t + φin(t))
Two-point PM modulationspectrum controlled at BB
Band
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Summary• Many wireless communication systems (mobile,
cordless, WLAN, GPS, … ) coexist• Variety of transceiver architectures represent
different trade-offs in performance• Digital baseband makes A/D and D/A conversion
compulsory• Design of a receiver part more critical than of
a transmitter, especially for full-duplex
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