TH71111

868/915MHz

FSK/FM/ASK Receiver

39010 71111

Page 3 of 22

Data Sheet

Rev. 013

June/07

1

Theory of Operation

1.1

General

With the TH71111 receiver chip, various circuit configurations can be arranged in order to meet a number of

different customer requirements. For FM/FSK reception the IF tank used in the phase coincidence

demodulator can also be constituted by a ceramic discriminator with a varactor diode to create an AFC

circuit. In ASK configuration, the RSSI signal is fed to an ASK detector, which is constituted by the

operational amplifier.

A double-conversion variant, called TH71112, is also available. This receiver IC allows a higher degree of

image rejection, achieved in conjunction with an RF front-end filter. Both RXICs have the same die. At the

TH71112, the second mixer (MIX2) is used to down-convert the first IF (IF1) to the second IF (IF2). At the

TH71111, MIX2 operates as an amplifier.

Efficient RF front-end filtering is realized by using a SAW, ceramic or helix filter in front of the LNA and by

adding an LC filter at the LNA output.

The TH71111 receiver IC consists of the following building blocks:

#

PLL synthesizer (PLL SYNTH) for generation of the local oscillator signal LO, parts of the PLL SYNTH

are: the high-frequency VCO1, the feedback divider DIV_32, a phase-frequency detector (PFD) with

charge pump (CP) and a crystal-based reference oscillator (RO)

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Low-noise amplifier (LNA) for high-sensitivity RF signal reception

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First mixer (MIX1) for down-conversion of the RF signal to the IF

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IF pre amplifier which is a mixer cell (MIX2) that operates as an amplifier

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IF amplifier (IFA) to amplify and limit the IF signal and for RSSI generation

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Phase coincidence demodulator (DEMOD) with third mixer (MIX3) to demodulate the IF signal

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Operational amplifier (OA) for data slicing, filtering and ASK detection

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Bias circuitry for bandgap biasing and circuit shutdown

1.2

Technical Data Overview

! Input frequency range: 800 MHz to 930 MHz

! Power supply range: 2.3 V to 5.5 V @ ASK

! Temperature range: -40 °C to +85 °C

! Standby current: 50 nA

! Operating current: 7.5 mA @ low gain mode

9.2 mA @ high gain mode

! Sensitivity: -112 dBm @ ASK 1)

-106 dBm @ FSK 2)

! Maximum data rate: 260 kbps NRZ @ ASK

180 kbps NRZ @ FSK

! Range of IF: 400 kHz to 22 MHz

! Maximum input level: -10 dBm @ ASK

0 dBm @ FSK

! Image rejection: > 45 dB (e.g. with 868.3 MHz

SAW front-end filter and at 10.7 MHz IF)

! Spurious emission: < -70 dBm

! Input frequency acceptance range: up to

±100 kHz

! RSSI range: 70 dB

! FM/FSK deviation range:

±2.5 kHz to ±80 kHz

! Maximum analog modulation frequency: 15 kHz

1) at 4 kbps NRZ, BER = 3

2)

at 4 kbps NRZ, BER = 3