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Datasheet: TH71081 (Melexis, Inc.)

868/915 MHZ Ask Transmitter/lo Source

 

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TH71081
868/915MHz
ASK Transmitter / LO Source
3901071081
Page 1 of 12
Data Sheet
Rev. 007
May/03
Features
!
Fully integrated, PLL-stabilized VCO
!
Frequency range from 850 MHz to 920 MHz
!
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
!
Differential output well-suited for loop antenna
!
Conforms to EN 300 220 and similar standards


Ordering Information
Part No.
Temperature Code
Package Code
TH71081
E (-40 C to 85 C)
DC (SOIC8)





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
!
Local oscillator signal generation



General Description

The TH71081 ASK 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.
LF
VEE
PS/DATA
ENTX
RO
VCC
OUT2
OUT1
TH71081
1
2
3
4
8
7
6
5
TH71081
868/915MHz
ASK Transmitter / LO Source
3901071081
Page 2 of 12
Data Sheet
Rev. 007
May/03
Document Content
1
Theory of Operation...................................................................................................3
1.1
General............................................................................................................................... 3
1.2
Block Diagram .................................................................................................................... 3
2
Functional Description ..............................................................................................4
2.1
ASK Modulation.................................................................................................................. 4
2.2
Frequency Modulation ........................................................................................................ 4
2.3
LO Source .......................................................................................................................... 4
2.4
Mode Control Logic............................................................................................................. 4
3
Pin Definition and Description ..................................................................................5
4
Electrical Characteristics ..........................................................................................6
4.1
Absolute Maximum Ratings ................................................................................................ 6
4.2
Normal Operating Conditions.............................................................................................. 6
4.3
Crystal Parameters............................................................................................................. 6
4.4
DC Characteristics.............................................................................................................. 7
4.5
AC Characteristics.............................................................................................................. 7
4.6
Output Power Selection ...................................................................................................... 7
5
Test Circuit .................................................................................................................8
5.1
Test circuit component list (Fig. 2) ...................................................................................... 8
6
Spectrum Plots...........................................................................................................9
7
Package Information................................................................................................10
8
Reliability Information..............................................................................................11
9
ESD Precautions ......................................................................................................11
10
Disclaimer .................................................................................................................12


TH71081
868/915MHz
ASK Transmitter / LO Source
3901071081
Page 3 of 12
Data Sheet
Rev. 007
May/03
1 Theory of Operation
1.1 General
As depicted in Fig.1, the TH71081 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 behaviour 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 R1
or by varying the voltage V
PS
at pin
PS/DATA. 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

LF 1
8 VEE
OUT1
OUT2
PA
VCC
7
6
mode
control
VCO
PFD
XOSC
div32
charge
pump
RF1
CF2
CF1
2
RO
XTAL
CX1
PS/DATA 4
VCC 5
ENTX
3
TH71081
868/915MHz
ASK Transmitter / LO Source
3901071081
Page 4 of 12
Data Sheet
Rev. 007
May/03
2 Functional
Description
2.1 ASK
Modulation
The TH71081 can be ASK-modulated by applying data directly at pin PS/DATA. This turns the PA on and off
and therefore leads to an ASK signal at the output.
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 LO
Source
Many applications require a stable RF source. For this purpose, the TH71081 can be used without modula-
tion as an easy-to-use, PLL-stabilized, continuous wave (CW) generator.
2.4 Mode Control Logic
The mode control logic allows two different modes of operation as listed in the following table. The mode
control pin ENTX is pulled-down internally. This guarantees that the whole circuit is shut down if this pin is
left floating.
ENTX
Mode
Description
0
TX standby
TX disable
1
TX active
TX enable



TH71081
868/915MHz
ASK Transmitter / LO Source
3901071081
Page 5 of 12
Data Sheet
Rev. 007
May/03
3 Pin Definition and Description
Pin No.
Name
I/O Type
Functional Schematic
Description
1 LF
analog
I/O
200
5p
LF
1
200
connection to loop filter,
charge pump output,
VCO tuning input
2 RO
analog
I/O
RO
2
28p
28p
37k
XOSC connection to XTAL,
Colpitts type crystal oscilla-
tor
3 ENTX
input
ENTX
3
1.1k
mode control input, CMOS-
compatible with internal
pull-down
4 PS/DATA analog
I/O
PS/DATA
4
200
20A
power-select and ASK input,
high-impedance comparator
logic

TX standby: I
PS
= 0
TX active: I
PS
= 20A
5
VCC
supply
positive power supply
6
OUT2
output
differential power amplifier
output, open collector
7 OUT1
output
VCC
VEE
VEE
VCC
OUT2
6
VEE
7
OUT1
differential power amplifier
output, open collector
8 VEE
ground
negative
power
supply
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