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TH7110

315/433MHz FSK/FM/ASK Double-Conversion Superheterodyne Receiver

Melexis Microelectronic Systems  

TH7110

315/433MHz FSK/FM/ASK

Double-Conversion Superheterodyne Receiver

General Description

The TH7110 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_8 and DIV_2,

a phase-frequency detector (PFD) with charge pump (CP) and a crystal-based reference oscillator (RO)

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

" First mixer (MIX1) for down-conversion of the RF signal to the first IF (IF1)

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

" IF amplifier (IFA) to amplify and limit the IF2 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, ASK detection and automatic-frequency control (AFC)

" Bias circuitry for bandgap biasing and circuit shutdown

With the TH7110 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 demodu-

lator can be constituted either by a ceramic resonator or an LC tank (optionally with varactor to create an AFC

circuit). In PLL demodulator configuration, the multiplier MIX3 forms a phase comparator. In ASK configurati-

on, the RSSI signal is feed to an ASK detector, which is constituted by the operational amplifier. The second

VCO (VCO2) can be used either as the VCO of a PLL demodulator or as the LO2 source of a second exter-

nal PLL in a multi-channel system. The following table briefly summarizes the various configurations.

FM/FSK

FM/FSK

FM/FSK

FM/FSK

ASK

ASK

Single-conversion configuration

narrow-band RX with ceramic demodulation

tank

wide-band RX with LC demod. tank and AFC

extended sensitivity RX with PLL demodulator

RX with RSSI-based demodulation

Double-conversion configuration

narrow-band RX with ceramic demodulation

tank

wide-band RX with LC demod. tank and AFC

extended sensitivity RX with PLL demodulator

multi-channel RX with ceramic demodulation

tank and external channel synthesizer

RX with RSSI-based demodulation

RX with RSSI-based demodulation and exter-

nal channel synthesizer

The preferred 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 a LC filter at the LNA output.

It is also possible to use the TH7110 in single-conversion configuration. This can be achieved by switching

the LO2 input of MIX2 from the on-chip PLL synthesizer to the pin IN_MIX2 by means of an internal switch

(done via pin SW_MIX2). Now MIX2 operates as an amplifier for the IF1 signal if an external pull-down re-

sistor at pin IN_MIX2 is added.

The same setting of MIX2 can be used for multi-channel applications. In this situation IN_MIX2 must be

driven by an external LO2 signal. This signal can be generated by the VCO2, which is mainly a bipolar tran-

sistor that can be configured as a varactor-tuned VCO. Furthermore, a second external PLL for channel

selection via LO2 tuning is required. This may be arranged by using the Melexis TH7010 PLL synthesizer

chip that can be controlled through a 3-wire bus serial interface. The reference signal for the external PLL

synthesizer can be directly taken from the crystal-based reference oscillator RO.

Datasheet Rev 2.3 July 2001

Page 2 of 22

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