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Datasheet: TH7108 (Melexis, Inc.)

868/915MHz Fsk/fm/ask Transmitter

 

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TH7108
868/915MHz
FSK/FM/ASK Transmitter
3901007108
Page 1 of 14
Data Sheet
Rev. 008
May/03
Features
!
Fully integrated, PLL-stabilized VCO
!
Frequency range from 850 MHz to 920 MHz
!
FSK through crystal pulling allows modulation
from DC to 40 kbit/s
!
High FSK deviation possible for wideband data
transmission
!
ASK achieved by on/off keying of internal
power amplifier
!
FM possible with external varactor
!
Wide power supply range from 2.2 V to 5.5 V
!
High over-all frequency accuracy
!
Very low standby current
!
Adjustable output power range from
-15 dBm to +1 dBm
!
Adjustable current consumption from
6.2 mA to 12.5 mA
!
FSK deviation and center frequency independ-
ently adjustable
!
Differential output well-suited for loop antenna
!
External clock available for C drive,
down to 1.9 V supply
!
"Clock only" mode
!
Conforms to EN 300 220 and similar standards


Ordering Information
Part No.
Temperature Code
Package Code
TH7108
E (-40 C to 85 C)
FC (QSOP16)



Application
Examples Pin
Description
!
Keyless car and central locking
!
Low-power
telemetry
!
Alarm and security systems
!
General digital data transmission
!
General analog audio signal transmission





General Description

The TH7108 FSK/ASK/FM transmitter IC is designed for applications in the European 868MHz industrial-
scientific-medical (ISM) band, according to the EN 300 220 telecommunications standard. It can also be
used for any other system with carrier frequencies ranging from 850 MHz to 920 MHz (e.g. for applications
in the US 915MHz ISM band).
The transmitter's carrier frequency f
c
is determined by the frequency of the reference crystal f
ref
that is used.
The integrated PLL synthesizer ensures that each RF value, ranging from 850 MHz to 920 MHz, can be
achieved by using a crystal with reference frequency according to: f
ref
= f
c
/N, where N = 32 is the PLL feed-
back divider ratio.
LF1
LF2
RO2
DATA
SUB
OUT1
VEE
VCC
TH7108
1
2
3
4
16
15
14
13
5
6
7
8
12
11
10
9
ENTX
RO1
CKOUT
ENCK
OUT2
PS
VCC
VEE
TH7108
868/915MHz
FSK/FM/ASK Transmitter
3901007108
Page 2 of 14
Data Sheet
Rev. 008
May/03
Document Content
1
Theory of Operation...................................................................................................3
1.1
General............................................................................................................................... 3
1.2
Block Diagram .................................................................................................................... 3
2
Functional Description ..............................................................................................4
2.1
FSK Modulation .................................................................................................................. 4
2.2
Frequency Modulation ........................................................................................................ 4
2.3
ASK Modulation.................................................................................................................. 4
2.4
Mode Control Logic............................................................................................................. 4
3
Pin Definition and Description ..................................................................................5
4
Electrical Characteristics ..........................................................................................7
4.1
Absolute Maximum Ratings ................................................................................................ 7
4.2
Normal Operating Conditions.............................................................................................. 7
4.3
Crystal Parameters............................................................................................................. 7
4.4
DC Characteristics.............................................................................................................. 8
4.5
AC Characteristics.............................................................................................................. 8
4.6
Output Power Selection ...................................................................................................... 8
5
Test Circuit .................................................................................................................9
5.1
Test circuit component list (Fig. 2) ...................................................................................... 9
6
Spectrum Plots.........................................................................................................10
7
Package Information................................................................................................12
8
Reliability Information..............................................................................................13
9
ESD Precautions ......................................................................................................13
10
Disclaimer .................................................................................................................14

TH7108
868/915MHz
FSK/FM/ASK Transmitter
3901007108
Page 3 of 14
Data Sheet
Rev. 008
May/03
1 Theory of Operation
1.1 General
As depicted in Fig.1, the TH7108 transmitter consists of a fully integrated voltage-controlled oscillator (VCO),
a divide-by-32 divider (div32), a phase-frequency detector (PFD) and a charge pump. An external loop filter
at pin LF determines the dynamic behavior of the PLL and suppresses reference spurious signals. The
VCO's output signal feeds the power amplifier (PA). RF signal power P
o
can be adjusted in six steps from
P
o
= 15 dBm to +1 dBm either by changing the value of resistor RPS
or by varying the voltage V
PS
at pin
PS. The open-collector differential output (OUT1, OUT2) can be used to either directly drive a loop antenna
or to be converted to a single-ended impedance by means of a balanced-to-unbalanced (balun) transformer.
For maximum available output power, the differential output should be matched to a load of about 1 k
.
Bandgap biasing ensures stable operation of the IC at a power supply range of 2.2 V to 5.5 V.




1.2 Block
Diagram



Fig. 1: Block diagram with external components

LF1
1
16
2
LF2
SUB
PA
mode
control
VCO
PFD
div32
charge
pump
RF1
RPS
CF2
CF1
VCC
PS
15
9
DATA
CKOUT
3
4
5
8
XOSC
div 8
RO2
RO1
XTAL
CX1
CX2
VCC 10
VEE
14
OUT1
OUT2
VCC
13
12
11
ENTX
VEE
ENCK
7
6
antenna
or
balun
TH7108
868/915MHz
FSK/FM/ASK Transmitter
3901007108
Page 4 of 14
Data Sheet
Rev. 008
May/03
2 Functional
Description
2.1 FSK
Modulation
A Colpitts crystal oscillator (XOSC) is used as the reference oscillator of a phase-locked loop (PLL) synthe-
sizer. FSK modulation is achieved by pulling the crystal (XTAL) through the data. So a CMOS-compatible
data stream applied at input DATA digitally modulates the XOSC. Two external pulling capacitors CX1 and
CX2 allow the FSK deviation and center frequency to be adjusted independently. At DATA = LOW CX2 is
connected in parallel to CX1 leading to the low-frequency component of the FSK spectrum (f
min
); while at
DATA = HIGH CX2 is deactivated and the XOSC is set to its high frequency, leading to f
max
.
An external reference signal can be directly AC-coupled to pin RO1. Then the TH7108 is used without an
XTAL. The reference signal has to contain the FSK (or FM) and sets the carrier frequency.
2.2 Frequency
Modulation
For FM operation an external varactor is required. It simply acts as a pulling capacitor connected in series to
the crystal. Then the analog modulation signal, applied through a series resistor, directly modulates the
XOSC.
2.3 ASK
Modulation
The TH7108 can be ASK-modulated by applying data directly at pin PS. This turns the PA on and off and
therefore leads to an ASK signal at the output.
2.4 Mode Control Logic
The mode control logic allows four different modes of operation as listed in the following table. The mode
control pins ENCK and ENTX are pulled-down internally. This guarantees that the whole circuit is shut down
if these pins are left floating.
The clock output CKOUT can be used to drive a C. This output can be activated by the ENCK pin as re-
quired for any specific application. Clock frequency is 1/8 of the reference crystal frequency.
ENCK
ENTX
Mode
Description
0
0
all OFF
whole circuit in standby
0
1
TX only
TX active, no clock available
1
0
clock only
TX standby and clock available
1
1
all ON
TX active and clock available




TH7108
868/915MHz
FSK/FM/ASK Transmitter
3901007108
Page 5 of 14
Data Sheet
Rev. 008
May/03
3 Pin Definition and Description
Pin No.
Name
I/O Type
Functional Schematic
Description
1 LF1
output
LF1
1
200
charge pump output, con-
nection to loop filter
2 SUB
ground
negative power supply, sub-
strate connection
3 DATA
input
DATA
3
1.8k
FSK data input,
CMOS-compatible
4 RO2
analog
I/O
RO2
4
XOSC FSK pulling pin,
MOS switch
5 RO1
analog
I/O
RO1
5
28p
28p
37k
XOSC connection to XTAL,
Colpitts type crystal oscilla-
tor
6 ENTX
input
ENTX
6
1.1k
mode control input, CMOS-
compatible with internal pull-
down
7 ENCK
input
ENCK
7
1.1k
mode control input, CMOS-
compatible with internal pull-
down


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