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J.Dąbrowski, Radioelectronics1
Radioelectronics‘RF CMOS 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/tsek26/
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Objectives of the course
• Learn principles of wireless digital communication transceivers
• Gain knowledge of RF front-end circuits• Learn design methods and techniques for RF
circuit design in CMOS technology• Understand the related possibilities and
limitations
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Organization of the course• Lectures 12 x 2h• Tutorials 6 x 2h (by Rashad Ramzan [email protected] )• Homework: optional• Laboratory work 3 x 4h (by Rashad Ramzan and
Henrik Fredriksson [email protected])• Course book: T.H.Lee, The Design of CMOS Radio-
Frequency Integrated Circuits, Cambridge Univ.Press, 2004 supporting book: Bosco Leung, VLSI for Wireless Communication, Prentice-Hall, Pearson Education, 2002/2004
• Examination: written exam
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Outline of the lecture
• Wireless communication systems today
• RF transceiver at glance
• CMOS RF design issues- architectures- circuits and devices
• Summary
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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
Also many other wireless applications and gadgets
UMTS CDMA2000
Zigbee
10,000
UWB100,000
4G directions
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Overview of Standards
1 W1, 2, 11Mb/s
QPSK25 ppm3000 kHz2400-2483CDMA802.11b(DSSS)
0.125, 0.25, 0.5, 2W
3840 (max)
QPSK0.1 ppm5000 kHz1920-1980 (Tx)2110-2170 (Rx)
W-CDMA/ TD-CDMA
WCDMA(UMTS)
1,4,100 mW1000GFSK20 ppm1000 kHz2400-2483CDMA/ FDMA/FH
Bluetooth
Peak PowerRate(kb/s)
Modulation Technique
FrequencyAccuracy
ChannelSpacing
Frequencyband (MHz)
Access Scheme
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 (Tx)1805-1850 (Rx)
TDMA/FDMA/ TDD
DCS-1800
OQPSK
π/4 QPSK
GMSK
GMSK
N/A1250 kHz
824-849 (Tx) 869-894 (Rx)
CDMA/ FDMAIS-95
200 Hz30 kHz824-849 (Tx) 869-894 (Rx)
TDMA/FDMA
IS-54
50 Hz1728 kHz1880-1900TDMA/FDMA/ TDD
DECT
90 Hz200 kHz890-915 (Tx)935-960 (Rx)
TDMA/FDMA/ TDD
GSM
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RF Transceiver at Glance
RFSection
BasebandSection
• RF Section – analog, high frequencies
• Baseband Section - mostly digital today (DSP), low frequencies
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Digital Transmitter
Upconverter/Modulator
PowerAmplifier
Carrier
Modulation & DSPADC
Basebandsignal
Digital baseband section (compression, coding,
modulation, shaping ) RF section (up-conversion, filtering, power gain)
DAC
Tradeoff between power efficiency and spectral efficiency
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Digital Receiver
Low NoiseAmplifier
Carrier
DownConverter ADC
Basebandsignal
Digital baseband section (equalization, demodulation, decoding, decompression)
RF section (image rejection, low noise gain, down conversion, channel selection)
RFFilter
Demodulator & DSP DAC
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CMOS RF design issues
• Disciplines in RF design• Key goals for ICs for RF transceiver
implementation• Why CMOS technology ?• Old and new receiver architectures
for CMOS• Circuits and devices
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Disciplines required in RF system design
RF Design
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RF Circuit Design OctagonMulti-objective approach
RF Design
In digital design only one main trade-off between speed and power
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Ultimate objective• Single-chip transceiver• Minimum external components• Inductors and capacitors integrated on chip
RFSection
BasebandDSP & Ctrl
Duplexeror switch
Battery or power supply
Crystal
Basebandinput/output
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Bluetooth CMOS TRx from Alcatel (2001)
Low-IF Rx and quadrature TxRF front-end
Layout of single chip TRx (first commercial with integrated BB and ARM processors + memory)
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WLAN CMOS TRx from Intel
Intel RFIC transceiver on 0.18 µm TSMC CMOS technology (Taiwan Semiconductor Manufacturing Corporation).
This IEEE 802.11a (in 5 GHz band) transceiver employs a direct-conversion architecture and includes an internal synthesizer. This is Intel's first RFIC used in a WLAN product.
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Why CMOS Technology• Submicron MOSFETs, 180,130, 90 nm today, very fast,
fmax>100GHz, perform well up to 10 GHz or more• Good linearity for higher signal swing• With multiple metal layers good capacitors and inductors
(QL up to 20) can be integrated on a chip• Upper metal layers far from Si substrate – reduce substrate losses• Lower substrate doping helps to isolate RF blocks and reduce losses• Large digital bocks (DSP & control) can be integrated on one chip
(but introduce substrate noise), Bipolar process not suitable• CMOS on Si cheaper from other technologies (BiCMOS, or CMOS
on GaAs, SiGe)• Many successful RF CMOS designs performed recently
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Old & New receiver architectures
• Superheterodyne receiver /double conversion(good sensitivity and selectivity, good image rejection but tradeoffs)
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)
BB signal
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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 suppress
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Old & New receiver architectures (cont’d)
• Direct receiver (homodyne) –(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) 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)
LO Leakage fLO = fRF fIF = 0
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Direct 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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Old & New receiver architectures (cont’d)
• Low-IF receiver
RFFilter
LNA
LO
I Q
DC notch + LPF 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
Polyphase filtersupports IQ rejection
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Low-IF receiver (cont’d)
fk ffLO,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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Need for IQ down conversion
-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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Need for IQ down conversion (cont’d)
sFSK (t) = cos(ωIF t + ϕ(t))
dϕ(t)/dt = k xBB (t)
s1 (t) = cos(ωIF ( t-t1) + ϕ(t-t1))= cos(ωIF t – 900+ ϕ(t-t1))= sin(ωIF t + ϕ(t-t1))
y(t) = sin(ϕ(t) - ϕ(t-t1)) + sin(2ωIF t + ϕ(t) + ϕ(t-t1))
yout(t) = sin(ϕ(t) - ϕ(t-t1))≅ t1dϕ(t)/dt = kt1 xBB (t)
Example:
900
LPFsFSK
s1
yout
Quadrature detection
But if ωIF = 0:
yout(t) = sin(ϕ(t) - ϕ(t-t1))+ sin(ϕ(t) + ϕ(t-t1))
so the detection cannot be achieved since the other component is folded
y
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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, otherwise crosstalk
High-power signal
FDD or TDD,respectively
Leakage of LO
Also effect on Rx can be critical
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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 can be destroyed and EVM rises
Tx measures output when BB signal is absent and introduces offset in BB stage to compensate for the carrier leakage
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Circuits and devices
A suspended spiral inductor of about 100 nHon a heavily doped CMOS substrate. This element enabled the first RF CMOS circuits at 900 MHz.Without inductors you can hardly neutralize parasitic capacitances in CMOS
Today lightly doped substrates and upper-metal layers enable good inductors on chip
Low-noise amplifier styles commonly used in CMOS. (a) Common gate circuit, robust against parasitics, moderate noise figure. (b) Common source circuit, lowest noise figure.
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Circuits and devices (cont’d)
Differential style must be preferred to suppress common mode substrate noise and even order distortions
CMOS oscillators require good Q factors to suppress own noise (white and 1/f)
Shield helps to reduce substrate currents
But still eddy-currents
L
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Circuits and devices (cont’d)
Circuit techniques of minimizing Phase Noise, 2nd harmonic can be suppressed and less 1/f noise is upconverted in this way
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Circuits and devices (cont’d)
MOSFETs as switches enable discrete tuning to enhance freq. range and compensate for production variations (tolerances).
The same technique is popular to calibrate for IQ mismatch
CMOS process tolerances can be largebut a circuit correction is possible → DfC
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Summary• Wireless communication systems (mobile, cordless,
WLAN, GPS, … ) are in continuous progress• Wireless communication systems are very complex
multidisciplinary field • Design of RF IC’s is a multi-objective task• CMOS technology proves to be increasingly
competitive for RF IC’s design (even higher frequencies)
• RF CMOS is an attractive research field