Radioelectronics ‘RF CMOS Transceiver...

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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/


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


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


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


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


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


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


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.


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


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


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


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


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


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.


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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Circuit techniques of minimizing Phase Noise, 2nd harmonic can be suppressed and less 1/f noise is upconverted in this way



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

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