EVB71112

868/915MHz Receiver

Evaluation Board Description

39012 71112 01

Page 3 of 14

EVB Description

Rev. 011

June/07

1

Theory of Operation

1.1

General

With the TH71112 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.

The superheterodyne configuration is double conversion where MIX1 and MIX2 are driven by the internal

local oscillator signals LO1 and LO2, respectively. This allows a high degree of image rejection, achieved in

conjunction with an RF front-end filter. 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.

A single-conversion variant, called TH71111, is also available. Both Receiver ICs have the same die. At the

TH71111 the second mixer MIX2 operates as an amplifier.

The TH71112 receiver IC consists of the following building blocks:

#

PLL synthesizer (PLL SYNTH) for generation of the first and second local oscillator signals LO1 and LO2,

parts of the PLL SYNTH are: the high-frequency VCO1, the feedback dividers DIV_16 and DIV_2,

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 first IF (IF1)

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Second mixer (MIX2) for down-conversion of the IF1 to the second IF (IF2)

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IF amplifier (IFA) to amplify and limit the IF2 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

EVB Technical Data Overview

! Input frequency range: 750 MHz to 990 MHz

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

2.7 V to 5.5 V @ FSK

! 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: -109 dBm @ ASK 1)

-103 dBm @ FSK 2)

! Range of first IF1: 10 MHz to 80 MHz

! Range of first IF2: 400 kHz to 22 MHz

! Maximum input level: -10 dBm @ ASK

0 dBm @ FSK

! Image rejection: > 60 dB (e.g. with 868.3 MHz

SAW front-end filter and at 10.7 MHz IF2)

! 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

filter loss

For more detailed information, please refer to the latest TH71112 data sheet revision