Texas Instruments TRF4903, Руководство пользователя, Страница: 13 / 26

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PCB Hardware Overview
4.7.1 European ISM Frequency Band
The European 868-MHz to 870-MHz ISM band is not covered in the preconfigured system, but it can be
modified by changing software variables; download new software configurations through the JTAG
connector. No hardware changes are needed, but the antenna matching is not optimized for this band.
See the Operating the TRF4903 Demo Kit in the 868-MHz EU ISM Band application note (SWRA047) for
further information. The firmware for the 868-MHz EU band can be downloaded from the
http://www.ti.com/ismrf website.
4.7.2 External Antenna
Significant range performance may be achieved when an external antenna is used. The actual
performance improvement will depend on the antenna design and proper impedance matching. A solder
pad for a SMA connector is provided on the circuit board. The antenna can be mounted onto the SMA
connector. Jumper (JP1) setting must be moved to connect the external antenna to the rest of the RF front
end. Shorting pins 2 and 3 of JP1 with a 0-
Ω
resistor connects the circuit board antenna. To connect an
external antenna, open pins 2 and 3 and short pins 1 and 2 with a 0-
Ω
resistor. Figure 7 shows the pin-out
configuration at the silk screen. Table 3 lists information for some antenna suppliers. If the PCB antenna is
not used, leave it unconnected, remove the matching components from each end, and substitute one
100-
Ω
resistor at each end; this will prevent unwanted coupling between the PCB antenna and the RF
signal.
Figure 7. JP1 Pin-Out Configuration
Table 3. Antenna Suppliers
Supplier Web Site Part Number ISM Band
Nearson www.nearson.com S467AM-915S US
S467AH-868S European
MaxRad www.maxrad.com MEXR902SM US
Mobilemark www.mobilemark.com PSWN3-925S US
PSTNS-900S European
W. Badland Ltd. www.badland.co.uk Various models US/ European
Radiall/Larsen www.radialllarsen.com Various models US
SPDA24832 European
4.7.3 RS-232C Port
The circuit board is designed for communication to the MSP430 microcontroller through the RS232 serial
port. The UART driver is implemented in firmware and is used in the RF evaluation mode.
4.7.4 On-Board LDO Voltage Regulator
In normal operation, the battery is connected directly to the circuit board power through R31. There is a
footprint for a low dropout (LDO) regulator for cases where a higher-voltage power supply is used instead
of the on-board batteries. To add an LDO regulator, remove R31 and install Texas Instruments regulator
TPS76330DBV at the U3 footprint.
TRF4903 With MSP430 Demonstration and Development Evaluation Kit SWRU010A – October 2004 – Revised May 2005 13