MELEXIS TH71112 Datasheet
TH71112
868/915MHz
FSK/FM/ASK Receiver
Features
! Double superhet architecture for high degree of image rejection
! FSK for digital data and FM reception for analog signal transmission
! FM/FSK demodulation with phase-coincidence demodulator
! Low current consumption in active mode and very low standby current
! Switchable LNA gain for improved dynamic range
! RSSI allows signal strength indication and ASK detection
! Surface mount package LQFP32
Ordering Information
Part No. Temperature Range Package
TH71112 -40 °C to 85°C LQFP32
Application Examples
! General digital and analog 868 MHz or 915 MHz ISM band usage
! Low-power telemetry
! Alarm and security systems
! Keyless car and central locking
! Pagers
Technical Data Overview
! Input frequency range: 800 MHz to 930 MHz
! Power supply range: 2.5 V to 5.5 V
! Temperature range: -40 °C to +85 °C
! Operating current: 7.5 mA at low gain and 9.2 mA at high gain mode
! Standby current: < 100 nA
! Sensitivity: -109 dBm
! Sensitivity: -102 dBm
! Range of first IF: 10 MHz to 80 MHz
! Range of second IF: 455 kHz to 21.4 MHz
! Maximum input level: –10 dBm at ASK and 0 dBm at FSK
! Image rejection: > 65 dB (e.g. with SAW front-end filter and at 10.7 MHz 2
! Spurious emission: < -70 dBm
! Input frequency acceptance: ±50 kHz (with AFC option)
! RSSI range: 70 dB
! Frequency deviation range: ±5 kHz to ±120 kHz
! Maximum data rate: 80 kbit/s NRZ
! Maximum analog modulation frequency: 15 kHz
1)
at ± 8 kHz FSK deviation, BER = 3⋅10-3 and phase-coincidence demodulation
2)
at ± 50 kHz FSK deviation, BER = 3⋅10-3 and phase-coincidence demodulation
1)
with 40 kHz second IF filter BW (incl. SAW front-end filter loss)
2)
with 150 kHz second IF filter BW (incl. SAW front-end filter loss)
nd
IF)
TH71112 Data Sheet Page 1 of 20 Nov. 2001
3901071112 Rev. 005
TH71112
868/915MHz
FSK/FM/ASK Receiver
General Description
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)
" Low-noise amplifier (LNA) for high-sensitivity RF signal reception
" First mixer (MIX1) for down-conversion of the RF signal to the IF1
" second mixer (MIX2) for down-conversion of the IF1 to the second IF (IF2)
" 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
With the T H71112 receiver c hip, various circuit c onfigurations c an be arranged in or der to m eet a num ber of
different custom er requirements . For FM/FSK reception the IF tank used in the phase coincidence dem odulator can be constituted either by a ceramic resonator or an LC tank (optionally with a varactor diode to create
an AFC circuit). In ASK configuration, the RSSI signal is feed to an ASK detector, which is constituted by the
operational amplifier.
Demodulation Type of receiver
FM / FSK
FM / FSK
ASK
The superheterodyne configuration is double conversion where MIX1 and MIX2 are driven by the internal
local oscillator signals LO1 and LO2, r espectively. This allows a high degree of im age rejec tion, achieved in
conjunction with an RF frontend filter. Efficient RF frontend f iltering is realized by using a SAW, ceram ic 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 RXICs have the same die. At the
TH71111 the second mixer MIX2 operates as an amplifier.
narrow-band RX with ceramic demodulation tank
wide-band RX with LC demodulation tank
RX with RSSI-based demodulation
TH71112 Data Sheet Page 2 of 20 Nov. 2001
3901071112 Rev. 005
Block Diagram
TH71112
868/915MHz
FSK/FM/ASK Receiver
IN_DEM
OUT_IFA
15 16
14
RSSI
21
FPC2
13
FBC1
12
IN_IFA
11
VEE_IF
10
OUT_MIX2
932
VCC_MIX
8
IF1N
7
IF1P
6
VEE_MIX
5
24
23
OUTP
OUTN
20
19
OAP
OAN
18
OUT_OA
OA
VCC_BIAS
17
VEE_BIAS
22
MIX3
ENRX
BIAS
28
VCC_PLL
27
VEE_RO
25
IFA
RO
RO
26
PFD
IF2
CP
LO2
DIV_2
LF
29
MIX2
IF1
DIV_16
LO1
VCO1
MIX1
IN_MIX1
4
OUT_LNA
GAIN_LNA
VEE_LNAC
1
LNA
IN_LNA
31
VEE_LNA
30
VCC_LNA
32
Fig. 1: TH71112 block diagram
TH71112 Data Sheet Page 3 of 20 Nov. 2001
3901071112 Rev. 005
TH71112
868/915MHz
FSK/FM/ASK Receiver
Frequency Planning
Frequency planning is straightforward for single-conversion applications because there is only one IF that
might be chosen, and then the only possible choice is low-side or high-side injection of the LO1 s ignal (which
is now the one and only LO signal in the receiver).
The receiver’s double-conver sion architecture requires careful frequenc y planning. Besides the desired RF
input signal, there are a number of s purious signals that may cause an undesired response at the output.
Among them are the image of the RF signal (that must be suppressed by the RF front-end f ilter), spurious
signals injected to the first IF ( IF1) and their im ages which could be m ixed down to the sam e sec ond IF (IF2)
as the desired RF signal (they must be suppressed by the LC filter at IF1 and/or by low-crosstalk design).
By configuring the TH71112 for double conversion and using its internal PLL synthesizer with fixed feedback
divider ratios of N1 = 16 (DIV_16) and N2 = 2 (DIV_2) , four types of down-conversion ar e possible: low-s ide
injection of LO1 and LO2 (low - low), LO1 low-side and LO2 high-side (low-high), LO1 high-side and LO2
low-side (high-low) or LO1 and LO2 high-s ide (high-high). T he following table sum m arizes som e equations
that are useful to calculate the crystal reference frequency (REF), the firs t IF (IF1) and the VCO1 or firs t LO
frequency (LO1), respectively, for a given RF and second IF (IF2).
Injection type high-high low-low high-low low-high
REF (RF – IF2)/30 (RF – IF2)/34 (RF + IF2)/30 (RF + IF2)/34
LO1
32•REF 32•REF 32•REF 32•REF
IF1 LO1 – RF RF – LO1 LO1 – RF RF – LO1
LO2
2•REF 2•REF 2•REF 2•REF
IF2 LO2 – IF1 IF1 – LO2 IF1 – LO2 LO2 – IF1
The following table depicts generated, desired, pos sible images and som e undesired s ignals cons idering the
examples of 868.3 MHz and 915 MHz RF reception at IF2 = 10.7 MHz.
Signal type RF =
868.3 MHz
Injection type high-high
REF / MHz 28.58667
LO1 / MHz 914.77333
IF1 / MHz 46.47333
LO2 / MHz 57.17333
RF image/MHz 961.24667
IF1 image/MHz 67.87333
RF =
868.3 MHz
low-low
25.22353
807.15294
61.14706
50.44706
746.00588
39.74706
RF =
868.3 MHz
high-low low-high high-high
29.3 25.85294 30.14333
937.6 827.29412 964.58667
69.3 41.00588 49.58667
58.6 51.70588 60.28667
1006.9 786.28824 1014.17
47.9 62.40588 70.98667
RF =
868.3 MHz
RF = 915
MHz
RF = 915
MHz
low-low
26.59706
851.10588
63.89412
53.19412
787.21176
42.49412
RF = 915
MHz
high-low low-high
30.85667 27.22647
987.41333 871.24706
72.41333 43.75294
61.71333 54.45294
1059.83 827.49412
51.01333 65.15294
RF = 915
MHz
The selection of the ref erence crystal frequency is based on som e assumptions. As for example: the f irst IF
and the image frequencies should not be in a radio band where strong interfering signals might occur
(because they could represent parasitic receiving s ignals), the LO1 s ignal should be in the range of 800 MHz
to 915 MHz (because this is the optimum frequency range of the VCO1). Furtherm ore the first IF should be
as high as possible to achieve highest RF image rejection. The colum ns in bold depict the selec ted f r equenc y
plans to receive at 868.3 MHz and 915 MHz, respectively.
TH71112 Data Sheet Page 4 of 20 Nov. 2001
3901071112 Rev. 005
TH71112
868/915MHz
FSK/FM/ASK Receiver
Pin Definition and Descripti on
Pin No. Name I/O Type Functional Schematic Description
3 OUT_LNA analog
output
31 IN_LNA analog
input
1 VEE_LNAC ground
2 GAIN_LNA analog
input
IN_LNA
31
GAIN_LNA
2
5k
400
Ω
OUT_LNA
3
VEE_LNAC
1
LNA open-collector output,
to be connected to external
LC tank that resonates at RF
LNA input, approx.
26Ω single-ended
ground of LNA core
(cascode)
LNA gain control (CMOS
input with hysteresis)
4 IN_MIX1 analog
input
IN_MIX1
4
Ω
13
Ω
13
500µA
MIX1 input, approx. 33Ω
single-ended
5 VEE_MIX ground LNA biasing ground
6 IF1P analog I/O open-collector output, to be
IF1P
6
7 IF1N analog I/O
VEE
VCC
20p
2x500µA
20p
VEE
IF1N
connected to external LC
tank that resonates at first IF
7
open-collector output, to be
connected to external LC
tank that resonates at first IF
8 VCC_MIX supply MIX1 and MIX2 positive
supply
9 OUT_MIX2 analog
output
OUT_MIX2
9
130
6.8k
Ω
230µA
MIX2 output, approx. 330Ω
output impedance
10 VEE_IF ground ground for MIX2, IFA and
DEMOD
TH71112 Data Sheet Page 5 of 20 Nov. 2001
3901071112 Rev. 005
TH71112
868/915MHz
FSK/FM/ASK Receiver
Pin No. Name I/O Type Functional Schematic Description
11 IN_IFA analog
input
VCC
IN_IFA
VCC
IFA input, approx. 2.2kΩ
input impedance
FBC1
12
IFA feedback capacitor
VEE
to be connected to external
IFA feedback capacitor
positive supply for IFA,
11
VEE
FBC2
13
VCC
VEE
2.2k
2.2k
200µA
VEE
12 FBC1 analog I/O to be connected to external
13 FBC2 analog I/O
14 VCC_IF supply
DEMOD
15 OUT_IFA analog I/O
IFA output and MIX3 input
(of DEMOD)
OUT_IFA
15
40µA
16 IN_DEM analog
input
IN_DEM
16
47k
DEMOD input, to MIX3 core
17 VCC_BIAS supply
positive supply of general
bias system and OA
18 OUT_OA analog
output
OUT_OA
Ω
50
OA output, 40uA current
drive capability
18
19 OAN analog
input
20 OAP analog
input
OAN
19
20µA
Ω
50
Ω
50
negative OA input, input
voltage limited to approx.
between pins OAP
pp
OAP
0.7 V
and OAN
negative OA input, input
20
voltage limited to approx.
0.7 V
between pins OAP
pp
and OAN
TH71112 Data Sheet Page 6 of 20 Nov. 2001
3901071112 Rev. 005
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