LINEAR LTC6602 User Guide Manual

DESIGN IDEAS L

Programmable Baseband Filter for Software-Defined UHF RFID Readers

by Philip Karantzalis

Introduction Radio frequency identification (RFID) Tag signal detection requires mea- is an auto-ID technology that identi- suring the time interval between signal fies any object that contains a coded transitions (a data “1” symbol has a

tag. A UHF RFID system consists of a longer interval than a data “0” symbol).

reader (or interrogator) that transmits The reader initiates a tag inventory by information to a tag by modulating sending a signal that instructs a tag –30 an RF signal in the 860MHz–960MHz to set its backscatter data rate and

frequency range. Typically, the tag is encoding. RFID readers can operate

passive—it receives all of its operating in a noisy RF environment where

energy from a reader that transmits many readers are in close proximity.

a continuous-wave (CW) RF signal. A The three operating modes, single- –80

tag responds by modulating the reflec- interrogator, multiple interrogator

FREQUENCY (k Hz)

tion coefficient of its antenna, thereby and dense-interrogator, define the

Figure 1. Filter response

backscattering an information signal spectral limits of reader and tag sig-

for a 15k Hz–150k Hz passband

to the reader. nals. Software programmability of the

receiver provides an optimum balance of reliable multitag detection and high with variable gain and bandwidth and a

DESIGN IDEAS

data throughput. The programmable dual analog-to-digital converter (ADC).

Programmable Baseband Filter for

reader contains a high linearity direct The LTC6602 dual, matched, program-

Software-Defined UHF RFID Readers

.........................................................27 conversion I and Q demodulator, low mable bandpass filter can optimize

Philip Karantzalis noise amplifiers, a dual baseband filter high performance RFID readers.

µModule LED Driver Integrates All

5V 3V GA IN (d B)

Circuitry, Including the Inductor, in a Surface Mount Package .............29 David Ng

Low Power Boost Regulator with VDDIN VDDA VDDD

Dual Half-Bridge in 3mm × 2mm DFN

I CHANNEL

Drives MEMS and Piezo Actuators CHANNEL

INPUT

.........................................................31 OUTPUT

Jesus Rosales

3V Q CHANNEL

LTC6602 CHANNEL

INPUT

Synchronous Boost Converter with OUTPUT Fault Handling Generates 5V at TRANSMITTER

0.1µF MUTE CLKIO

500m A in 1cm2 of Board Space .........33 MUTE INPUT

Eddy Wells DOUT PAR/SER

CS V+ NC CLKCNTL

Robust DC/DC Step-Down Converter 3V

in 3mm × 3mm DFN Resists 60V

SCLK VOUT RBIAS SDO

Input Surges .....................................34

Chuen Ming Tan SDI 68.1k CS

4W LED Driver Includes Power Switch, Compensation Components and

Schottky in 16-Pin MSOP ...................36 LTC2630

8-BIT DAC GNDVOCM

Keith Szolusha

3mm × 3mm, 16-Bit ADC Brings

Accurate, Precise High Side VREF

Current Sensing to Tight Spaces .......37 OUTPUT Leo Chen

Dual 8A DC/DC µModule Regulator Is

SPI CONTROL OF LTC6602 SETS THE FILTER GAIN

Easily Paralleled for 16A ..................38

AND THE LOWPASS AND HIGHPASS DIVISION RATIO

Eddie Beville and Alan Chern

Self-Contained 3A µModule Buck Regulator Produces 0.8V–24V Output from 3.6V–36V Input ..............40

David Ng SCK SDI CS2CS1

Figure 2. An Adaptable RFID baseband filter with SPI control

Linear Technology Magazine • September 2009