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Datasheet: TH72002 (Melexis, Inc.)

Transmitter - 315MHz, Ask (SOIC8)

 

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TH72002
315MHz
ASK Transmitter
3901072002
Page 1 of 14
Data Sheet
Rev. 003
Feb./03
PR
ELI
MIN
AR
Y
Features
!
Fully integrated PLL-stabilized VCO
!
Frequency range from 290 MHz to 350 MHz
!
Single-ended
RF
output
!
ASK achieved by on/off keying of internal
power amplifier up to 40 kbit/s
!
Wide power supply range from 1.9 V to 5.5 V
!
Very low standby current
!
Low
voltage
detector
!
High over-all frequency accuracy
!
Adjustable output power range from
-12 dBm to +8.5 dBm
!
Adjustable current consumption from
3.5 mA to 10.7 mA
!
Conforms to EN 300 220 and similar standards
Ordering Information
Part No.
Temperature Code
Package Code
TH72002
K (-40 C to 125 C)
DC (SOIC8)
Application Examples
Pin Description
!
General digital data transmission
!
Tire Pressure Monitoring System (TPMS)
!
Remote Keyless Entry (RKE)
!
Low-power
telemetry
!
Alarm and security systems
!
Garage door openers
!
Home
automation
General Description
The TH72002 ASK transmitter IC is designed for applications in the 315 MHz industrial-scientific-medical
(ISM) band. It can also be used for any other system with carrier frequencies ranging
from 290 MHz to 350 MHz.
The transmitter's carrier frequency f
c
is determined by the frequency of the reference crystal f
ref
. The
integrated PLL synthesizer ensures that each RF value, ranging from 290 MHz to 350 MHz, can be achieved
by using a crystal with a reference frequency according to: f
ref
= f
c
/N, where N = 32 is the PLL feedback
divider ratio.
n. c.
ASKDTA
VEE
ENTX
ROI
VCC
PSEL
OUT
TH72002
1
3
4
2
8
6
5
7
TH72002
315MHz
ASK Transmitter
3901072002
Page 2 of 14
Data Sheet
Rev. 003
Feb./03
PR
ELI
MIN
AR
Y
Document Content
1
Theory of Operation...................................................................................................3
1.1 General .............................................................................................................................. 3
1.2 Block Diagram.................................................................................................................... 3
2
Functional Description ..............................................................................................4
2.1 Crystal Oscillator................................................................................................................ 4
2.2 ASK Modulation ................................................................................................................. 4
2.3 Crystal Pulling .................................................................................................................... 4
2.4 Output Power Selection ..................................................................................................... 5
2.5 Lock Detection ................................................................................................................... 5
2.6 Low Voltage Detection ....................................................................................................... 5
2.7 Mode Control Logic ............................................................................................................ 6
2.8 Timing Diagrams................................................................................................................ 6
3
Pin Definition and Description ..................................................................................7
4
Electrical Characteristics ..........................................................................................8
4.1 Absolute Maximum Ratings................................................................................................ 8
4.2 Normal Operating Conditions ............................................................................................. 8
4.3 Crystal Parameter .............................................................................................................. 8
4.4 DC Characteristics ............................................................................................................. 9
4.5 AC Characteristics ........................................................................................................... 10
4.6 Output Power Steps ......................................................................................................... 10
5
Test Circuit ...............................................................................................................11
5.1 Test circuit component list to Fig. 5 .................................................................................. 11
6
Package Information................................................................................................12
7
Reliability Information..............................................................................................13
8
ESD Precautions ......................................................................................................13
9
Disclaimer .................................................................................................................14
TH72002
315MHz
ASK Transmitter
3901072002
Page 3 of 14
Data Sheet
Rev. 003
Feb./03
PR
ELI
MIN
AR
Y
1
Theory of Operation
1.1 General
As depicted in Fig.1, the TH72002 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 (CP). An
internal loop filter determines the dynamic behavior of the PLL and suppresses reference spurious signals. A
Colpitts crystal oscillator (XOSC) is used as the reference oscillator of a phase-locked loop (PLL)
synthesizer. The VCO's output signal feeds the power amplifier (PA). The RF signal power P
out
can be
adjusted in four steps from P
out
= 12 dBm to +8.5 dBm, either by changing the value of resistor RPS
or by
varying the voltage V
PS
at pin PSEL. The open-collector output (OUT) can be used either to directly drive a
loop antenna or to be matched to a 50Ohm load. Bandgap biasing ensures stable operation of the IC at a
power supply range of 1.9 V to 5.5 V.
1.2 Block
Diagram
Fig. 1: Block diagram with external components
VEE
XOSC
PA
XBUF
VCO
PLL
CP
PFD
32
PSEL
RPS
ROI
XTAL
8
5
3
2
antenna
matching
network
OUT
7
CX1
1
ASKDTA
6
VCC
mode
control
ENTX
4
low
voltage
detector
TH72002
315MHz
ASK Transmitter
3901072002
Page 4 of 14
Data Sheet
Rev. 003
Feb./03
PR
ELI
MIN
AR
Y
2
Functional Description
2.1 Crystal
Oscillator
A Colpitts crystal oscillator with integrated functional capacitors is used as the reference oscillator for the PLL
synthesizer. The equivalent input capacitance CRO offered by the crystal oscillator input pin ROI is about
18pF. The crystal oscillator is provided with an amplitude control loop in order to have a very stable
frequency over the specified supply voltage and temperature range in combination with a short start-up time.
2.2 ASK
Modulation
The PLL transmitter can be ASK-modulated by
applying a data stream directly at the pin
ASKDTA. This turns the internal current
sources of the power amplifier on and off and
therefore leads to an ASK signal at the output.
ASKDTA
Description
0
Power amplifier is turned off
1
Power amplifier is turned on (according
to the selected output power step)
2.3 Crystal
Pulling
A crystal is tuned by the manufacturer to the
required oscillation frequency f
0
at a given load
capacitance CL and within the specified
calibration tolerance. The only way to pull the
oscillation frequency is to vary the effective load
capacitance CL
eff
seen by the crystal.
Figure 2 shows the oscillation frequency of a
crystal as a function of the effective load
capacitance. This figure also illustrates the
relationship between the external pulling
capacitor and the center frequency.
It can be seen that the pulling sensitivity
increases with the reduction of CL. For high-
accuracy ASK applications, a higher load
capacitance should be chosen in order to
reduce the frequency drift caused by the
tolerances of the chip and the external pulling
capacitor.
Fig. 2: Crystal pulling characteristic
f
o
f
eff
CL
eff
CL
R1
C1
C0
L1
XTAL
CL=
CX1 CRO
CX1+CRO
TH72002
315MHz
ASK Transmitter
3901072002
Page 5 of 14
Data Sheet
Rev. 003
Feb./03
PR
ELI
MIN
AR
Y
2.4 Output Power Selection
The transmitter is provided with an output power selection feature. There are four predefined output power
steps and one off-step accessible via the power selection pin PSEL. A digital power step adjustment was
chosen because of its high accuracy and stability. The number of steps and the step sizes as well as the
corresponding power levels are selected to cover a wide spectrum of different applications.
The implementation of the output power control
logic is shown in figure 3. There are two
matched current sources with an amount of
about 8 A. One current source is directly
applied to the PSEL pin. The other current
source is used for the generation of reference
voltages with a resistor ladder. These reference
voltages are defining the thresholds between
the power steps. The four comparators deliver
thermometer-coded control signals depending
on the voltage level at the pin PSEL. In order to
have a certain amount of ripple tolerance in a
noisy environment the comparators are
provided with a little hysteresis of about 20 mV.
With these control signals, weighted current
sources of the power amplifier are switched on
or off to set the desired output power level
(Digitally Controlled Current Source). The
LOCK, ASK signal and the output of the low
voltage detector are gating this current source.
Fig. 3: Block diagram of output power control circuitry
There are two ways to select the desired output power step. First by applying a DC voltage at the pin PSEL,
then this voltage directly selects the desired output power step. This kind of power selection can be used if
the transmission power must be changed during operation. For a fixed-power application a resistor can be
used which is connected from the PSEL pin to ground. The voltage drop across this resistor selects the
desired output power level. For fixed-power applications at the highest power step this resistor can be
omitted. The pin PSEL is in a high impedance state during the "TX standby" mode.
2.5 Lock
Detection
The lock detection circuitry turns on the power amplifier only after PLL lock. This prevents from unwanted
emission of the transmitter if the PLL is unlocked.
2.6 Low Voltage Detection
The supply voltage is sensed by a low voltage detect circuitry. The power amplifier is turned off if the supply
voltage drops below a value of about 1.85 V. This is done in order to prevent unwanted emission of the
transmitter if the supply voltage is too low.
ASKDTA
&
&
&
PSEL
&
&
RPS
OUT
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