LINEAR Wideband RF ICs for Power Detection and Control – Design Note 335 by James Wong and Vladimir Dvorkin Owner's Manual User Guide

advertisement

Wideband RF ICs for Power Detection and Control – Design Note 335 James Wong and Vladimir Dvorkin

Introduction placed as close as possible to the antenna without forming Radio frequency devices are being deployed in ever a “T” connection on the microstrip line and immediately followed by capacitor C1 and the LTC5509. Ideally, C1, R1

increasing numbers, not just in cell phones and cordless

and LTC5509 should be placed on the same side of the

telephones. Other applications include 802.11 wireless

LAN, RFID (Radio Frequency Identification) tags, inven- PCB as the Tx output microstrip line to the antenna. The component values shown here should be used as a

tory monitors, satellite transceivers, fixed wireless

reference. In the actual product implementation, compo-

access and wireless communications infrastructure. All

RF devices must carefully monitor and control their RF nent values may differ slightly depending on the output impedance of the Tx PAs, antenna impedance, compo-

power transmission to comply with government regula-

nent placement and PC board parasitics.

tion and minimize RF interference with other radio devices. For this reason, accurate RF power detection is

An RFID Reader Application

important in both RF receivers and transmitters.

RFID (Radio Frequency Identification) is a promising tech- This article presents some solutions using Linear nology for many monitoring and tracking applications,

Technology’s versatile family of high frequency Schottky ,LTC and LT are registered trademarks and Thin SOT is a trademark of

Linear Technology Corporation.

diode detectors. Table 1 summarizes the features of this

family and lists more applications. C1

ANTENNAR1

A Dual-Band Mobile Phone Transmitter Power

Control Application Tx PA MODULE CELL BAND

Figure 1 is a simplified block diagram illustrating transmit

LTC5509 DIPLEXER power control for a dual band mobile phone (the receiver SHDN RFIN is not shown here). In this example, a 324Ω, 1% tolerance GND GND resistor (R1) followed by a 2.2p F capacitor (C1) form a VOUT VCC PCS BAND

Li-Ion0.1µF

coupling circuit with 18d B to 20d B coupling factor at 850MHz to 1850MHz, referenced to the LTC®5509 RF input pin. C1 is also a DC blocking capacitor. R1 should

MOBILE PHONE BB/DSP VPC

DN335 F01

have a tolerance of 1% while C1 should be 2% to 5%. The coupling circuit (R1 and C1) introduces about 0.15d B to Figure 1. A Dual Band Mobile Phone Transmit Power

0.2d B losses into the main signal line. R1 should be Control Using a Resistive Tap

Table␣ 1. Summary of RF Detector Specifications and Applications DEVICE FREQUENCY RANGE PACKAGE DYNAMIC RANGE/FEATURES APPLICATIONS

LTC5505-1 300MHz to 3GHz Thin SOTTM –28d Bm to 18d Bm* General Purpose, Phones, ISM

LTC5505-2 300MHz to 3GHz Thin SOT –32d Bm to 12d Bm* General Purpose, Phones, ISM

LTC5507 100 KHz to 1GHz Thin SOT –34d Bm to 14d Bm* General Purpose LF & Broadband Detection

LTC5508 300MHz to 7GHz SC–70† –32d Bm to 12d Bm* General Purpose, WLAN, Microwave

LTC5509 300MHz to 3GHz SC–70† –30d Bm to 6d Bm** Mobile Phones Tx Power Control

LTC5532 300MHz to 7GHz Thin SOT Adjustable Gain & Starting Voltage Precision RSSI & Envelope Detection

*Gain compression extends the dynamic range with a tradeoff of reduced linearity in the transfer characteristic. **No gain compression. †Smallest package.