Wireless Transceiver RF Front-Ends An overview of the main architectures in RF front-end design Fraidun Akhi April 1, 2003 Electrical and Computer Engineering.

Wireless Transceiver Wireless Transceiver RF Front-EndsRF Front-Ends

Wireless Transceiver Wireless Transceiver RF Front-EndsRF Front-Ends

An overview of the main An overview of the main architectures in RF front-end architectures in RF front-end

designdesign

Fraidun AkhiFraidun AkhiApril 1, 2003April 1, 2003

Electrical and Computer EngineeringElectrical and Computer EngineeringAuburn UniversityAuburn University

ContentsContents

The complete transceiver system modelThe complete transceiver system model

- What role does the RF front-end - What role does the RF front-end play?play?

An overview of RF front-end architecturesAn overview of RF front-end architectures

- Advantages and disadvantages- Advantages and disadvantages Industry trendsIndustry trends Design exampleDesign example

- RFMD’s 802.11b WLAN chipset- RFMD’s 802.11b WLAN chipset ConclusionConclusion

Transceiver System ModelTransceiver System Model

Typical RF Front-End DesignTypical RF Front-End Design

Superheterodyne ArchitectureSuperheterodyne Architecture

AdvantagesAdvantages

- High performance- High performance

- Low power- Low power

- Avoid DC offset- Avoid DC offset

- Low Design Risk- Low Design Risk

- Easier to design LNA - Easier to design LNA and Mixerand Mixer

DisadvantagesDisadvantages

- High cost due to - High cost due to large component large component quantitiesquantities

- Not as compact as - Not as compact as other designsother designs

Direct Conversion ArchitectureDirect Conversion Architecture

AdvantagesAdvantages

- Low Cost- Low Cost

- Eliminates IF SAW - Eliminates IF SAW filter, IF PLL, image filter, IF PLL, image filter, and mixerfilter, and mixer

- 30% less parts than - 30% less parts than superheterodynesuperheterodyne

DisadvantagesDisadvantages- Hard to achieve I/Q - Hard to achieve I/Q quadrature balance at quadrature balance at RFRF- LO self mixing causes - LO self mixing causes DC offset DC offset - 10% more power - 10% more power consumption than consumption than superheterodynesuperheterodyne

Low IF ArchitectureLow IF Architecture

AdvantagesAdvantages- Low cost- Low cost- Eliminates IF SAW filter, - Eliminates IF SAW filter, IF PLL, image filterIF PLL, image filter- No DC offset due to LO - No DC offset due to LO self mixingself mixing

DisadvantagesDisadvantages- Hard to achieve I/Q - Hard to achieve I/Q quadrature balance at RF quadrature balance at RF - Requires LPF’s with higher - Requires LPF’s with higher passbands, and higher passbands, and higher performing ADC’sperforming ADC’s

A GSM Phone RF Front-EndA GSM Phone RF Front-End

Industry TrendsIndustry Trends

More integration and fewer componentsMore integration and fewer components- Direct conversion favored- Direct conversion favored

- Power consumption gap is closing- Power consumption gap is closing Single chip systems Single chip systems

- Analog/digital baseband, RF, codecs, power - Analog/digital baseband, RF, codecs, power management, everything included!management, everything included!- TI has promissed a single chip GSM/GPRS phone - TI has promissed a single chip GSM/GPRS phone by 2004by 2004

SiGe gaining popularity due to advantages such SiGe gaining popularity due to advantages such as higher speed andas higher speed and lower costlower cost

Design ExampleDesign Example

TransmitterTransmitter

Transmitter System ParametersTransmitter System Parameters

Transmitter input level = 100 mVppTransmitter input level = 100 mVpp PA output ~ 25 dBm (300 mW)PA output ~ 25 dBm (300 mW)

- Can be as high as 27 dBm (500 mW)- Can be as high as 27 dBm (500 mW)

- Up to 1W allowable in the ISM band- Up to 1W allowable in the ISM band Filter insertion loss (S21) < 1 dBFilter insertion loss (S21) < 1 dB

ReceiverReceiver

Receiver System ParametersReceiver System Parameters

Filter insertion loss (S21) < 1 dBFilter insertion loss (S21) < 1 dB LNA/Mixer cascaded gain = 35 dBLNA/Mixer cascaded gain = 35 dB

- Cascaded IP3 = -25 dBm- Cascaded IP3 = -25 dBm

- GSM requires IP3 < -19 dBm- GSM requires IP3 < -19 dBm

- Cascaded NF = 4.1 dB- Cascaded NF = 4.1 dB Receiver cascaded gain = 70 dBReceiver cascaded gain = 70 dB

- Cascaded IP3 = -100 dBuV- Cascaded IP3 = -100 dBuV

- 5 to 35 dB depending on gain- 5 to 35 dB depending on gain

ConclusionsConclusions

There are practical advantages to each There are practical advantages to each front-end architecturefront-end architecture

Compactness, integration, and economics Compactness, integration, and economics provide practical and aesthetic provide practical and aesthetic advantages that give direct conversion advantages that give direct conversion systems the upper handsystems the upper hand

ReferencesReferences

Dr. Foster Dai’s ELEC 6970 notesDr. Foster Dai’s ELEC 6970 notes Texas Instruments - Texas Instruments - www.ti.comwww.ti.com RF Micro Devices – RF Micro Devices – www.rfmd.comwww.rfmd.com