TH71111
868/915MHz
FSK/FM/ASK Receiver
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:
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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
First mixer (MIX1) for down-conversion of the RF signal to the IF
IF pre amplifier which is a mixer cell (MIX2) that operates as an amplifier
IF amplifier (IFA) to amplify and limit the IF signal and for RSSI generation
Phase coincidence demodulator (DEMOD) with third mixer (MIX3) to demodulate the IF signal
Operational amplifier (OA) for data slicing, filtering and ASK detection
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
! 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
! Sensitivity: -112 dBm @ ASK 1)
-106 dBm @ FSK 2)
! Input frequency acceptance range: up to
! RSSI range: 70 dB
±100 kHz
! Maximum data rate: 260 kbps NRZ @ ASK
180 kbps NRZ @ FSK
! FM/FSK deviation range: ±2.5 kHz to ±80 kHz
! Maximum analog modulation frequency: 15 kHz
1) at 4 kbps NRZ, BER = 3⋅10-3, 180 kHz IF filter BW, without SAW front-end-filter loss
2) at 4 kbps NRZ, BER = 3⋅ ± 20 kHz FSK deviation, 180 kHz IF filter BW, without SAW front-end-filter loss
10-3,
39010 71111
Rev. 013
Page 3 of 22
Data Sheet
June/07
MELEXIS [ Melexis Microelectronic Systems ]
