TRF4900

SINGLE-CHIP RF TRANSMITTER

SLWS092F – JULY 2000 – REVISED JANUARY 2002

2

POST OFFICE BOX 655303

ISM band standards

Europe has assigned a new unlicensed frequency band of 868 MHz to 870 MHz. This new band is specifically

defined for short range devices with duty cycles from 0.1% to 100% in several sub-bands. The existing 433-MHz

band for short-range devices in Europe has the great disadvantage of very high usage. The new European

frequency band, due to the duty cycle assignment, allows a reliable RF link and makes many new applications

possible.

The North American unlicensed ISM (industrial, scientific, and medical) band covers 902 MHz to 928 MHz

(center frequency of 915 MHz) and is suitable for short range RF links.

transmitter

The transmitter consists of an integrated VCO, a complete fully-programmable direct digital synthesizer, and

a power amplifier. The internal VCO can be used with an external tank circuit or an external VCO. The divider,

prescaler, and reference oscillator require only the addition of an external crystal and a loop filter to provide a

complete DDS with a typical frequency resolution of 230 Hz.

The 8-bit FSK frequency deviation register determines the frequency deviation in FSK mode. The modulation

itself is done in the direct digital synthesizer, hence no additional external components are necessary.

Since the typical RF output power is approximately 7 dBm, no additional external RF power amplifier is

necessary in most applications.

The TRF4900 RF transmitter is suitable for use in applications that include the TRF6900 RF transceiver.

baseband interface

The TRF4900 can easily be interfaced to a baseband processor such as the Texas Instruments MSP430

ultralow-power microcontroller (see Figure 1). The TRF4900 serial control registers are programmed by the

MSP430, and the MSP430 performs baseband operations in software.

Transmit Data

Lock Detect

Mode Select

Serial Control Data

Serial Control Clock

Serial Control Strobe

TX_DATA

LOCKDET

MODE

STDBY

DATA

CLOCK

STROBE

PA_OUT

TRF4900

TRANSMITTER

+

DISCRETES

RF Section

Programmable

Digital I/O Pins

MSP430

Family

µC

Microcontroller

Section

Antenna

Standby

RF Out

Figure 1. System Block Diagram for Interfacing to the MSP430 Microcontroller