TH71221 datasheet(4/44 Pages) MELEXIS

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TH71221

27 to 930MHz

FSK/FM/ASK Transceiver

39010 071221

Page 4 of 44

Data Sheet

Rev. 005

June/07

Theory of Operation

1.1

General

The main building block of the transceiver is a programmable PLL frequency synthesizer that is based on an

integer-N topology. The PLL is used for generating the carrier frequency during transmission and for

generating the LO signal during reception. The carrier frequency can be FSK-modulated either by pulling the

crystal or by modulating the VCO directly. ASK modulation is done by on/off keying of the power amplifier.

The receiver is based on the principle of a single conversion superhet. Therefore the VCO frequency has to

be changed between transmit and receive mode. In receive mode, the default LO injection type is low-side

injection.

The TH71221 transceiver IC consists of the following building blocks:

Low-noise amplifier (LNA) for high-sensitivity

RF signal reception with switchable gain

Mixer (MIX) for RF-to-IF down-conversion

IF amplifier (IFA) to amplify and limit the IF

signal and for RSSI generation

Phase-coincidence FSK demodulator with

external ceramic discriminator or LC tank

Operational amplifier (OA1), connected to

demodulator output

Operational amplifier (OA2), for general use

Peak detector (PKDET) for ASK detection

Control logic with 3wire bus serial control

interface (SCI)

Reference oscillator (RO) with external crystal

Reference divider (R counter)

Programmable divider (N/A counter)

Phase-frequency detector (PFD)

Charge pump (CP)

Voltage controlled oscillator (VCO) with internal

varactor

Power amplifier (PA) with adjustable output

power

1.2

Technical Data Overview

Frequency range: 300 MHz to 930 MHz in

programmable user mode

Extended frequency range with external VCO

varactor diode: 27 MHz to 930 MHz

315 MHz, 433 MHz, 868 MHz or 915 MHz fixed-

frequency settings in stand-alone mode

Power supply range: 2.2 V to 5.5 V

Temperature range: -40 °C to +85 °C

Standby current: 50 nA

Operating current in receive: 6.5 mA (low gain)

Operating current in transmit: 12 mA (at -2 dBm)

Adjustable RF power range: -20 dBm to +10dBm

Sensitivity: -105 dBm at FSK with 180 kHz

IF filter BW

Sensitivity: -107 dBm at ASK with 180 kHz

IF filter BW

Max. data rate with crystal pulling: 20 kbps NRZ

Max. data rate with direct VCO modulation:

115 kbps NRZ

Max. input level: -10 dBm at FSK

and -20 dBm at ASK

Input frequency acceptance:

± 10 to ± 150 kHz

(depending on FSK deviation)

FM/FSK deviation range:

±2.5 to ±80 kHz

Analog modulation frequency: max. 10 kHz

Crystal reference frequency: 3 MHz to 12 MHz

External reference frequency: 1 MHz to 16 MHz

1.3

Note on ASK Operation

Optimum ASK performance can be achieved by using an 8-MHz crystal for operation at 315 MHz, 434 MHz

and 915 MHz. For details please refer to the software settings shown in sections 7.4 and 7.6. FSK operation

is the preferred choice for applications in the European 868MHz band.

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