RF2958 Просмотр технического описания (PDF) - RF Micro Devices

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RF2958

2.4GHz SPREAD-SPECTRUM TRANSCEIVER

RF Micro Devices 

RF2958

Theory of Operation

The RF2958 is a single-chip transceiver designed specifically for IEEE 802.11b wireless LAN applications. In addition to

typical transceiver functions of RF conversion of both the transmit and receive signals, the RF2958 incorporates a low-

noise amplifier (LNA) and a dual phase-locked loop (PLL) frequency synthesizer to reduce end-product component

count and to simplify integration into end-products. The RF2958 uses a superheterodyne frequency conversion architec-

ture in both the transmit and receive signal paths for superior performance in 802.11b applications. It also incorporates

power conservation functionality to increase battery life in portable and mobile applications. When used with the RF3002

baseband processor and RF5189 power amplifier (PA), the RF2958 is part of a complete PHY solution for 802.11b appli-

cations (see figure below, 2.4GHz IEEE 802.11b Chipset Block Diagram).

RF2958

RF5189

fC = 2450 MHz

BW = 100 MHz

TX/RX

SWITCH

ANTENNA

DIVERSITY

SWITCH

TX PE

RX PE

RF PLL

fC = 374 MHz

BW = 20 MHz

Serial Data

Interface

PLL/Power

Control Registers

SDI

RX VGC

ANT SEL

RX I

REF

VREF

RX Q

TX VGC

TX I

TX Q

IF PLL

RF3002

RXVGC

DAC

CCA

RX VGC

I IN

ADC

Data Converter

Reference

Q IN

ADC

TX VGC

DAC

I OUT

DAC

Q OUT

DAC

802.11

Preamble/

Header

Control

Port

Mode Control

802.11

Preamble/

Header

Tx Length

Tx Signal

Service

CCA

LNA GS

RX DATA

RX RDY

DATA CLK

SPI

TX RDY

TX DATA

RX PE

TX PE

M CLK

SYSTEM ARCHITECTURE

The overall system architecture is based around a superheterodyne conversion process. For the transmitter side, the

baseband in-phase (I) and quadrature (Q) signal components are converted to an intermediate frequency (IF) of

374MHz. An external SAW filter is used to filter out undesired spurious frequencies. The IF is then converted to the over-

the-air radio frequency (RF) between 2.412GHz and 2.483GHz using low-side injection. The RF output drives a PA to

amplify the signal to the desired power level at the antenna. Generally the PA is followed by a TX/RX switch and a band

pass filter which eliminates the undesired sideband resulting from the mixing process before broadcasting the signal

through the antenna.

The receiver is the inverse of this process. The signal from the antenna passes through the band pass filter, which is in

this case acting as a pre-selection filter. The received signal passes through the integrated LNA and is converted to an IF

of 374MHz. The signal then passes through a SAW filter, which acts to reject adjacent channels as defined by the

802.11 standard. Due to the bandwidth of this filter, adjacent channels must be at least 20MHz apart. The filtered IF sig-

nal is then downconverted to baseband I and Q components.

The local oscillators required by the mixing process are generated by internal IF and RF PLL frequency synthesizers.

These are controlled through a three-wire serial data interface.

Rev A0 050209

11-271

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