MICROWAVES & RF 108 MAY 2003

Flexible Chip Set Arms802.11a/b/g WLANs This software-driven, dual-

chip solution provides theperformance and versatilityneeded to support the threemajor WLAN standards atdata rates to 54 Mb/s.

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better support of multimedia services. To enable these emerging WLAN standards,RF Micro Devices (Greensboro, NC) has developed the model RFCS5420 soft-ware-driven, flexible dual-band, two-chip solution that works across all three stan-dards and allows seamless connectivity among all three systems.

A chip set designed for connectivity to IEEE 802.11a/b/g networks will requirethree main building blocks: 1. A radio subsystem with transceivers capable of operating at 2.4 and 5 GHz. 2. A modem that supports orthogonal-frequency-division-multiplex (OFDM) andcomplementary-code-keying (CCK) modulation schemes. 3. A unified media-access controller (MAC) with support for IEEE 802.11a/b/g andthe extensions to these standards.

The RFCS5420 chip set consists of a model RF5425 transceiver integrated cir-cuit (IC) and a model RF5421 bandband/MAC IC. Both ICs are implemented in 0.18-µm, +1.8-VDC complementary-metal-oxide-semiconductor (CMOS) technologywhich offers extremely low power consumption in both transmit and receive modes.The RFCS5420 chip set can be functionally viewed as a composite of distinct IEEE802.11a and IEEE 802.11b/g chip sets, each with its own radio, modem, and MACsubsystems that share a common host interface. The RF5425 transceiver is basedon a True Zero-IF CMOS radio-transceiver architecture. Only front-end amplifiersand bandpass filters are needed for a complete dual-band 2.4- and 5-GHz WLANradio solution.

ireless local-area networks (WLANs) are now well established

in business enterprise networks, and growing in home appli-

cations. Until now, such networks have been based upon the

IEEE 802.11b standard at 2.4 GHz. But increasing demands for

more WLAN bandwidth and faster data rates have fostered the

newer IEEE 802.11a and g standards with greater security and w

CHIP SET

visit PlanetEE.com

JIM BOHAC Marketing ManagerRF Micro Devices (San JoseOffice), 7628 Thorndike Rd.,Greensboro, NC 27409; (336)664-1233, FAX: (336) 931-7454,Internet: www.rfmd.com.

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The RF5421 baseband/MAC ICincludes a complete implementation ofIEEE 802.11a/b/g CCK and OFDMmodems and an ARM9 processor thatexecutes the bulk of the processingfunctions required for MAC processing.The RF5421 also includes hardwareaccelerators for modem aiding func-tions and full-speed encryption andsecurity support. Together, the two ICsexecute all of the Layer 1 and 2 func-tions required for IEEE 802.11a/b/goperation, thereby freeing significant high-speed processing chores from a hostprocessor.

The RFCS5420 chip set (Fig. 1) sup-ports data rates to 11 Mb/s (1, 2, 5.5,and 11 Mb/s) in CCK mode at 2.4 GHzand data rates to 54 Mb/s (6, 9, 12,18, 24, 36, and 54 Mb/s) in OFDMmode at 2.4 and 5 GHz. The radiotransceiver operates in the 2.4-GHzindustrial-scientific-medical (ISM) band,the 4.9-to-5.1 GHz Japan band, and

the 5.15-to-5.35-GHz UNII band. Thechip set provides support for a widerange of modulation formats, includ-ing BPSK, QPSK, 16QAM, and 64QAM. The chip set’s unique AccuChan-nel equalization provides as much as 4-dB improvement in signal-to-noise ratio(SNR) in typical office environments,

which translates into a 32-percentincrease in WLAN range and about70-percent more coverage area whenoperating in OFDM mode.

The RF5425’s zero-IF radio IC fea-tures a direct-conversion architecture(Fig. 2), requiring only one mixer stageto convert the desired RF signals direct-ly to and from baseband signals with-out any IF stages and without the needfor external surface-acoustic-wave (SAW)filters. Most zero-IF radio designs alsointegrate the low-noise amplifier (LNA),voltage-controlled oscillator (VCO),and the baseband filters on a mono-lithic die. In fact, such integrated single-chip zero-IF transceivers have performedwell for many years in cellular and pagerapplications and they are beginning toemerge in WLAN radio designs as well.A major advantage of the zero-IF archi-tecture on CMOS is that it enables theimplementation of a full dual-bandtransceiver on a monolithic die with a

MICROWAVES & RF 111 MAY 2003

1. The RFCS5420 WLAN chip set con-sists of the RF5425 2.4/5-GHz RFtransceiver IC and the RF5421 base-band/MAC IC.

p~108,111,112,114,116,118 5/7/03 11:57 AM Page 111

MICROWAVES & RF 112 MAY 2003

minimum increase in die size comparedto a single-band implementation. Thezero-IF radio architecture eliminates anIF stages, reducing complexity andpower consumption. Furthermore, sev-eral on-chip circuits, i.e. synthesizers, canbe shared for both bands.

Of course, no radio architecture isideal. Some of the common RF prob-lems inherent with the zero-IF architectureare DC offset, flicker noise, and LOpulling. DC offsets are mainly generatedby the LO leakage, which self-mixes,thereby creating a DC component in the

signal chain that affects the receiverperformance and can cause the RFstages to saturate. Flicker noise, alsoknown as 1/f noise, is low-frequencydevice noise that can corrupt signalsin the receiver chain. Flicker noise is morepronounced with the zero-IF architec-ture because of the direct conversion tolow-frequency baseband signals. Anoth-er concern with direct conversion is thepulling of the LO by the power-ampli-fier (PA) output, which affects the directupconversion process. This is becausethe high-power PA output, which hasa spectrum centered around the LOfrequency, can disturb (or pull) the fre-quency of the transmitter VCO.

The RF5425 incorporates propri-etary filters designed to provide supe-rior adjacent-channel and alternateadjacent-channel rejection while min-imizing noise contributions. An inno-vative VCO-design and frequency-plan-ning architecture minimizes phase noiseand LO pulling in the transmitter.

The other RF effects of zero-IF CMOStransceivers are mitigated by a combi-nation of RF design techniques andbaseband algorithms. A DC offset loopoperates in conjunction with the base-band to dynamically correct for DCoffset. Similarly, in-phase/quadrature (I/Q)mismatch is measured and correctedby the baseband at time of system ini-tialization or channel changes. Close cou-pling of the RF5421 and RF5425 pro-vide optimal performance for the zero-IFWLAN radio implementation.

The RF5421 baseband/MAC ICprovides the baseband, MAC, securi-ty and host functions for the RF5425radio (Fig. 3). It is designed with pro-prietary RF Micro Devices algorithmsto achieve maximum IEEE 802.11a/b/gsystem performance, using AccuChan-nel Equalization technology, advancedhardware security and a flexible MAC.The IC incorporates the following func-tional blocks: 1. An ARM9 processor with 16-kBcache memory for MAC software exe-cution supported by external SDRAM,SRAM, or Flash memory.2. An 802.11a/g OFDM modem.3. An 802.11b CCK modem.

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4. A programmableencryption/decryptionengine.5. Internal timers withmicrosecond resolution.6. PCI/CardBus/Mini-PCI interface support. 7. Power-managementcircuitry.

The decision to usea software MAC hasobvious benefits for theflexibility to supportthe IEEE 802.11a, b,and g protocols as wellas the quality-of-serviceand security standardssoon to be ratified bythe IEEE standardsbody. The RF MicroDevices’ Flexible MAC is software con-trolled, written in C++ language, andruns under the ThreadX real-time oper-ating system (RTOS). On-chip dedi-

cated hardware is provided to offloadvarious low-level operations for per-formance optimization. Implementa-tion of the MAC in software provides

a future-proof implementation for orig-inal-equipment manufacturers (OEMs).With the software based MAC, OEMscan track changes in the developing

MICROWAVES & RF 114 MAY 2003

RF5424RF transceiver IC

AGC

RxI,Q

TxI,Q

RF5421Baseband/MAC

IC

5 GHz

2.4 GHz

5 GHz

2.4 GHz

LNA

LNA

DC offsetcompensation

loop

Resonextproprietary

filters

Resonextproprietary

filters

PLL/VCO

Xtal

2. The RF5425 RF transceiver IC employs a zero-IF architecture to minimize mixers, filters, and othercomponents in the downconversion of 2.4- and 5-GHz signals to lower-frequency baseband signals.

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MICROWAVES & RF 116 MAY 2003

IEEE 802.11 standards and providefeature upgrades to installed hardwarevia software-update packages. All flex-ible MAC features can be downloadedto clients using remote software-updateprocedures controlled from a central man-agement database. This feature offers

OEMs the capability to provide softwareupdates and revenue-generating softwareenhancements to end customers.

This software-based MAC imple-mentation is referred to as the RFMDFlexible MAC architecture. RF MicroDevices has used the Flexible MAC

architecture to track IEEE standarddevelopments (e.g., IEEE 802.11i,e,h,k,and j) and to implement extensions tothe basic service set defined by the IEEEsuch as WiFi Protected Access and CiscoCCX in addition to providing a vehi-cle for customers to provide product dif-ferentiation through implementationof their own protocol extensions. TheRF5421 has been implemented with aprogrammable encryption/decryptionengine that is managed by the on-chipARM processor in order to implementFlexible MAC Enhanced Security (IEEE802.11i). This flexible architectureallows the RF5421 solution to be alignedwith the developing IEEE 802.11-TGiWorking Group proposals. In additionto supporting TGi standards basedsecurity proposals, the programmableencryption/decryption engine can beused to support proprietary securitysystems such as Cisco CCX. Current secu-rity modes supported by the RF5421include: Wired Equivalent Protection(WEP) 1 and 2, WiFi Protected Access(WPA) and Advanced Encryption Stan-dard (AES). These security modes areimplemented in hardware for maxi-mum system performance. TKIP andAES/CCM modes are also supported forfuture compatibility with evolving TGiproposals. The RF5420 chip set also pro-vides support for 802.1x authentication.

Multimedia applications are increas-ing the need for managed quality ofservice (QoS) in many applications. Inaccordance with the IEEE 802.11e stan-dard, the RFMD Flexible MAC hasprovisioned for eight independentlymanaged packet queues to supportimplementation of QoS dependent ser-vices. With the software-based architecturethe Flexible MAC can be used to imple-ment standards-based approaches toQoS or proprietary approaches inadvance of full standard ratification.

The IEEE 802.11 specifications allowfor reserved and optional fields in bea-con and other management frames with-in the IEEE 802.11 protocols. OEMs havetaken advantage of these fields to imple-ment network-management featurescommonly referred to as “SuperMAC”extensions. RFMD’s Flexible MAC

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allows OEMs to take full advantage ofthese SuperMAC extensions. Exam-ples of these features include dynamicdata-rate selection, client roaming sup-port, and a host of network-managementfeatures, such as link status reporting,and radio-link calibration.

With the Flexible MAC softwareand the two-chip CMOS implementa-tion, the RFCS5420 chip set can beembedded into a variety of WLANdevices. As an example, Fig. 4 shows afunctional block diagram for a basicclient CardBus or Mini-PCI WLANsolution based on the RF5425 andRF5421. This application illustrates

the level of system integration achiev-able with the chip set resulting in ahigh-yield, low-BOM cost, small form-factor design. In addition to the pair ofICs, the solution requires dual-banddiversity antennas, an antenna switchfor transmit/receive mode and diversi-ty functions, 2.4- and 5-GHz PAs, low-dropout regulators to supply the +1.8and +3.3 VDC needed by all devices, alow-cost band-select filter/diplexer forselecting 2.4- or 5-GHz band, 2-kb seri-al EEPROM for storing device config-uration data and MAC address, and1-MB SDRAM or SRAM for MACcode and data.

In addition, the RFCS5420 chip setcan be used to develop USB2.0 clientdevices, Ethernet Client Bridge devices,low-cost Access Points and Wirelessrouters, as well as embedded multi-media WLAN NICs. In summary, theRFCS5420 is an ideal solution to pro-vide cost-effective IEEE 802.11a/b/gnetwork connectivity while at the sametime providing a platform that willchange along with the continuouslyevolving IEEE standards activities. RFMicro Devices, 7628 Thorndike Rd.Greensboro, NC 27409; (336) 664-1233, FAX: (336) 931-7454, Internet:www.rfmd.com.

MICROWAVES & RF 118 MAY 2003

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I/QA/D

1-MB memory

32-b data

Multiportmemory controller

DMA

Cipherengine

MACARM9

processorw/cache

Timers

SerialEEPROM

controller

GPIO

I/QD/A

CCK &OFDM

modem

RF controlinterface

DMA

MACaccelerator

AuxiliaryADC

AuxiliaryDAC4

4

RF5424Wireless

LANtransceiver

RX I/Q

TX I/Q

External RFfunctions

4

RF5421802.11a/b/g Wireless LANBaseband/Media access

controller

DMA

Hostinterface

PCICardbusMini PCI

Clock andpower

management

SerialEEPROM

HostsystemPCICardbusMini PCI

SDRAM or SRAM

Ant.TX/RX

Rx (5 GHz)

Voltageregulator

3.3 V1.8 V

PA

PA

BPF

BPF

Diversityswitch

Tx I/Q

Rx I/Q

Control

40-MHzXTAL

RN5225

Tx (2.4 GHz)

Tx (5 GHz)

Rx (2.4 GHz)

32-b data

GPIO

SerialEEPROM

4 wireRN5221

PCI, Cardbus, or Mini PCI

3. The RF5421 baseband/media-access-controller (MAC) IC works with a flexible software MAC to support the IEEE 802.11a/b/gWLAN standards.

4. This functionalblock diagram showsa typical client Card-

Bus or Mini-PCI WLANdesign based on theRF5425 transceiver

and the RF5421 base-band/MAC ICs.

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