TH7111 Datasheet, PDF (2/20 Pages) List of Unclassifed Manufacturers – FSK /FM/ASK Receiver

TH7111
868/915MHz
FSK/FM/ASK Receiver
General Description
The TH7111 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)
" 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 TH7111 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 TH7111 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 a PLL synthesizer chip that can be con-
trolled 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.
TH7111 Data Sheet
3901007111
Page 2 of 20
Nov. 2001
Rev. 005