TH72031KDC Melexis Inc, TH72031KDC Datasheet - Page 5

• Manufacturer Part Number: TH72031KDC
• Description: 868/915 MHZ, FSK TRANSMITTER
• Manufacturer: Melexis Inc

Specifications of TH72031KDC

• Frequency: 868MHz, 915MHz
• Applications: Alarm and Security Systems, RKE
• Modulation Or Protocol: FSK
• Data Rate - Maximum: 40 kbps
• Power - Output: -11dBm ~ 9dBm
• Current - Transmitting: 5.1mA ~ 13.4mA
• Data Interface: PCB, Surface Mount
• Antenna Connector: PCB, Surface Mount
• Voltage - Supply: 1.9 V ~ 5.5 V
• Operating Temperature: -40°C ~ 125°C
• Package / Case: 8-SOIC (0.154", 3.90mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Features: -
• Memory Size: -
• Other names: Q3477881B

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 ap-
plied 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 thermome-
ter-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 signal and the
output of the low voltage detector are gating
this current source.
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 de-
sired 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.
3901072031
Rev. 010
Page 5 of 20
Fig. 4:
RPS
PSEL
Block diagram of output power control circuitry
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FSK Transmitter
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TH72031
868/915MHz
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Data Sheet
Jan/09
OUT