1 trx-intro

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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/


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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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


Outline of the lecture

• Wireless communication systems today

• RF transceiver architecture

• Architectures- receiver- transmitter

• 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

UMTS CDMA2000

Zigbee

10,000

UWB100,000

4G directions

LTE/WiMax


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


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


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


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


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


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


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


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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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


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


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


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


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

1 trx-intro

Documents

beat differential circuits

rf trx design

mixerinherent mirror spectrum

lo leakage lo

pa power control

quadrature iq mixer

rf filter

dc offset