ETC EVB72002

EVB72002
315MHz ASK Transmitter
Evaluation Board Description
General Description
The TH72002 evaluation board is designed to demonstrate the optimal performance of the transmitter IC in a
50Ohm environment with the minimum of external components. The TH72002
board is populated for ASK transmission. The power amplifier is optimally matched to 50 Ohm by means of
an antenna matching network for the resonant frequency of 315 MHz.
Board layout data in Gerber format is available on request.
Features
!
!
!
!
Fully integrated PLL-stabilized VCO
Frequency range from 380 MHz to 450 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
! Low voltage detector
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! High over-all frequency accuracy
! Very low standby current
! Adjustable output power range from
-15 dBm to +6 dBm
! Adjustable current consumption from
3.5 mA to 10.7 mA
! Conforms to EN 300 220 and similar
standards
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Ordering Information
Part No.
EVB72002-315
Applications
!
!
!
!
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General digital data transmission
Tire Pressure Monitoring System(TPMS)
Remote Keyless Entry (RKE)
Low-power telemetry
Alarm and security systems
390127200201
Rev. 002
!
!
!
!
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Garage door openers
Home automation
Remote controls
Local oscillator signal generation
EVB Description
Oct/02
EVB72002
315MHz ASK Transmitter
Evaluation Board Description
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
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3
Circuit Diagram ............................................................................................................7
4
PCB Top View ..............................................................................................................8
4.1
Board Connection ............................................................................................................................. 8
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5
Board Component Values ...........................................................................................9
6
Package Information..................................................................................................10
7
Disclaimer...................................................................................................................12
390127200201
Rev. 002
Page 2 of 12
EVB Description
Oct/02
EVB72002
315MHz ASK Transmitter
Evaluation Board Description
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 Pout can be
adjusted in four steps from Pout = –15 dBm to +6 dBm, either by changing the value of resistor RPS or by
varying the voltage VPS 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
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RPS
ENTX
4
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ROI
3
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PLL
mode
control
6
32
PSEL
ASKDTA
5
1
PA
7
OUT
antenna
matching
network
PFD
XOSC
XBUF
XTAL
CX1
VCC
Y
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A
CP
VCO
low
voltage
detector
2
8
VEE
Fig. 1: Block diagram with external components
390127200201
Rev. 002
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EVB Description
Oct/02
EVB72002
315MHz ASK Transmitter
Evaluation Board Description
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.
2.3
ASKDTA
Description
0
Power amplifier is turned off
1
Power amplifier is turned on (according
to the selected output power step)
Crystal Pulling
A crystal is tuned by the manufacturer to the
required oscillation frequency f0 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 CLeff seen by the crystal.
Figure 3 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 highaccuracy 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.
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XTAL
L1
C1
C0
CL eff
R1
fo
CL=
CX1 CRO
CX1+CRO
CL eff
Fig. 2: Crystal pulling characteristic
390127200201
Rev. 002
Page 4 of 12
EVB Description
Oct/02
EVB72002
315MHz ASK Transmitter
Evaluation Board Description
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 4. There are two
matched current sources with an amount of
about 8 µA. 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.
RPS
PSEL
&
ASKDTA
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&
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OUT
Fig. 3: Block diagram of output power control circuitry
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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.
typical values at TA = 23 °C and VCC ≥ 4 V
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2.5
Power step
0
1
2
3
4
Pout / dBm
< -70
-15
-6
0
6
RPS / kΩ
Ω
< 10
22
47
100
> 220
VPS / V
0.1
0.14 to 0.24
0.28 to 0.51
0.57 to 1.18
> 1.23
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.
390127200201
Rev. 002
Page 5 of 12
EVB Description
Oct/02
EVB72002
315MHz ASK Transmitter
Evaluation Board Description
2.7
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 pulleddown internally. This guarantees that the whole
circuit is shut down if this pin is left floating.
2.8
ENTX
Mode
Description
0
TX standby
TX disabled
1
TX active
TX enable
Timing Diagrams
After enabling the transmitter by the ENTX signal, the power amplifier remains inactive for the time ton, the
transmitter start-up time. The crystal oscillator starts oscillation and the PLL locks to the desired output
frequency within the time duration ton. After successful PLL lock, the LOCK signal turns on the power
amplifier, and then the RF carrier can be ASK modulated.
high
ENTX
low
high
LOCK
low
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high
ASKDTA
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low
P
RF carrier
t
t on
Fig. 4: Timing diagram for ASK modulation
For more detailed information, please refer to the latest TH72002 data sheet revision.
390127200201
Rev. 002
Page 6 of 12
EVB Description
Oct/02
EVB72002
315MHz ASK Transmitter
Evaluation Board Description
3 Circuit Diagram
OUT
CM2
LM
CM1
CM3
CB1
RPS
ROI
ENTX
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XTAL
CX1
1 2 3
1 2
VCC
GND
CB0
VCC
ENTX
GND
1 2 3
PSEL
VCC
OUT
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VCC
DATA
GND
P
5
6
n. c.
7
ASKDTA
8
VEE
LT
Fig. 5: Circuit diagram for FSK with 50 Ω matching network
390127200201
Rev. 002
Page 7 of 12
EVB Description
Oct/02
EVB72002
315MHz ASK Transmitter
Evaluation Board Description
4 PCB Top View
P
CM1
Melexis
LM
EVB72011 / 12 / 31 / 32 (1)
TX_output
CM2
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CM3
LT
CB1
RPS
8
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TH72002
1
4
CX1
XTAL
CB0
VCC
ENTX
1
VCC
Data
1
VCC
1
Board size is 23 mm x 34 mm
4.1
VCC
DATA
Board Connection
Power supply (1.9 V to 5.5 V)
ENTX
Mode control pin (see para. 2.7)
Input for ASK data (CMOS, see para. 2.2)
GND
Several ground pins
390127200201
Rev. 002
Page 8 of 12
EVB Description
Oct/02
EVB72002
315MHz ASK Transmitter
Evaluation Board Description
5 Board Component Values
Part
Size
Value
@ 315 MHz
Tolerance
Description
*CX1
0805
TBD
±5%
XOSC capacitor (∆f = ±20 kHz)
CM1
0805
TBD
±5%
impedance matching capacitor
CM2
0805
TBD
±5%
impedance matching capacitor
CM3
0603
TBD
±5%
impedance matching capacitor
CB0
0805
1 nF
±10%
blocking capacitor
CB1
0603
330 pF
±10%
blocking capacitor
output tank inductor
LT
0603
TBD
±5%
LM
0603
TBD
±5%
impedance matching inductor
RPS
0805
see para. 2.4
±10%
power-select resistor
XTAL
HC49/S
9.84375 MHz
fundamental wave
±30ppm
calibration
±30ppm temp.
*Notes: Value depends on crystal parameters
Your Notes
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390127200201
Rev. 002
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crystal, CL = 12 pF, C0, max = 7 pF, R1 = 60 Ω
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EVB Description
Oct/02
EVB72002
315MHz ASK Transmitter
Evaluation Board Description
6 Package Information
E1 E
1 2 3
D
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α
A1 A
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Fig. 6: SOIC8 (Shrink Small Outline Package)
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all Dimension in mm, coplanarity < 0.1mm
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A
A1
e
b
L
α
min
4.80
3.81
5.80
1.32
0.10
1.27
0.36
0.41
0°
max
4.98
3.99
6.20
1.72
0.25
0.46
1.27
8°
P
all Dimension in inch, coplanarity < 0.004”
390127200201
Rev. 002
min
0.189
0.150 0.2284 0.060 0.0040 0.05 0.014
0.016
0°
max
0.196
0.157 0.2440 0.068 0.0098
0.050
8°
Page 10 of 12
0.018
EVB Description
Oct/02
EVB72002
315MHz ASK Transmitter
Evaluation Board Description
Your Notes
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Rev. 002
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EVB Description
Oct/02
EVB72002
315MHz ASK Transmitter
Evaluation Board Description
7 Disclaimer
Devices sold by Melexis are covered by the warranty and patent indemnification provisions appearing in its
Term of Sale. Melexis makes no warranty, express, statutory, implied, or by description regarding the
information set forth herein or regarding the freedom of the described devices from patent infringement.
Melexis reserves the right to change specifications and prices at any time and without notice. Therefore, prior
to designing this product into a system, it is necessary to check with Melexis for current information. This
product is intended for use in normal commercial applications. Applications requiring extended temperature
range, unusual environmental requirements, or high reliability applications, such as military, medical lifesupport or life-sustaining equipment are specifically not recommended without additional processing by
Melexis for each application.
The information furnished by Melexis is believed to be correct and accurate. However, Melexis shall not be
liable to recipient or any third party for any damages, including but not limited to personal injury, property
damage, loss of profits, loss of use, interrupt of business or indirect, special incidental or consequential
damages, of any kind, in connection with or arising out of the furnishing, performance or use of the technical
data herein. No obligation or liability to recipient or any third party shall arise or flow out of Melexis’ rendering
of technical or other services.
© 2002 Melexis NV. All rights reserved.
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For the latest version of this document. Go to our website at
www.melexis.com
Or for additional information contact Melexis Direct:
Europe and Japan:
All other locations:
Phone: +32 1367 0495
E-mail: [email protected]
Phone: +1 603 223 2362
E-mail: [email protected]
QS9000, VDA6.1 and ISO14001 Certified
390127200201
Rev. 002
Page 12 of 12
EVB Description
Oct/02