TRF6900
SINGLE-CHIP RF TRANSCEIVER
SLAS213C – SEPTEMBER 1999 – REVISED MAY 2000
description
The TRF6900 single-chip solution is an integrated circuit intended for use as a low cost FSK transceiver to
establish a frequency-agile, half-duplex, bidirectional RF link. The device is available in a 48-lead TQFP
packageandisdesignedtoprovideafully-functionalmultichannelFMtransceiver. Thechipisintendedforlinear
(FM) or digital (FSK) modulated applications in the new 868 MHz European band and the North American 915
MHz ISM band. The single chip transceiver operates down to 2.2 V and is expressly designed for low power
consumption. The synthesizer has a typical channel spacing of approximately 230 Hz to allow narrow-band as
well as wide-band application. Due to the narrow channel spacing of the direct digital synthesizer (DDS), the
DDS can be used to adjust the TX/RX frequency and allows the use of inexpensive reference crystals.
Two fully-programmable operation modes, Mode0 and Mode1, allow extremely fast switching between two
preprogrammed settings (e.g., receive(RX)/transmit(TX); TX_frequency_0/TX_frequency_1;
RX_frequency_0/RX_frequency_1;…) without reprogramming the device. Each functional block of the
transceiver can be specifically enabled or disabled via the serial interface.
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 4.5 dBm, no additional external RF power amplifier is
necessary in most applications.
receiver
The integrated receiver is intended to be used as a single-conversion FSK receiver. It consists of a low noise
amplifier, mixer, IF amplifier, limiter, FM/FSK demodulator with an external LC tank circuit, and a data slicer. The
receive strength signal indicator ( RSSI ) can be used for fast carrier sense detection or as an on/off keying,
or amplitude shift keying, (OOK/ASK) demodulator. In the learning mode, during a learning sequence
(0,1,0,1,0,....), the initial tolerances of the LC demodulator tank circuit are compensated and an external
capacitor is charged to a dc voltage that is proportional to the average demodulation dc level. This level is the
zero reference for the data slicer to generate the logical levels of the data sequence that follow the learning
sequence. Using the internal data switch, the demodulated OOK and FSK signals are available at the same
DATA_OUT terminal.
baseband interface
The TRF6900 can easily be interfaced to a baseband processor such as the Texas Instruments MSP430 ultra
low-power microcontroller (see Figure 1). The TRF6900 serial control registers are programmed by the
MSP430 and the MSP430 performs baseband operations in software.
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