RF02
DETAILED FEATURE-LEVEL DESCRIPTION
The RF02 FSK transmitter is designed to cover the unlicensed frequency bands at 433, 868, and
915 MHz. The device facilitates compliance with FCC and ETSI requirements.
PLL
The programmable PLL synthesizer determines the operating frequency, while preserving accuracy
based on the on-chip crystal-controlled reference oscillator. The PLL’s high resolution allows the usage of
multiple channels in any of the bands. The FSK deviation is selectable (from 30 to 210 kHz with 30 kHz
increments) to accommodate various bandwidth, data rate and crystal tolerance requirements, and it is
also highly accurate due to the direct closed-loop modulation of the PLL. The transmitted digital data can
be sent asynchronously through the FSK pin or over the control interface using the appropriate
command.
RF Power Amplifier (PA)
The power amplifier has an open-collector differential output and can directly drive a loop antenna
with a programmable output power level. An automatic antenna tuning circuit is built in to avoid costly
trimming procedures and the so-called “hand effect.”
Crystal Oscillator
The chip has a single-pin crystal oscillator circuit, which provides a 10 MHz reference signal for the
PLL. To reduce external parts and simplify design, the crystal load capacitor is internal and
programmable. Guidelines for selecting the appropriate crystal can be found later in this datasheet.
The transmitters can supply the clock signal for the microcontroller, so accurate timing is possible
without the need for a second crystal. When the chip receives a Sleep Command from the microcontroller
and turns itself off, it provides several further clock pulses (“clock tail”) for the microcontroller to be able to
go to idle or sleep mode. The length of the clock tail is programmable.
Low Battery Voltage Detector
The low battery voltage detector circuit monitors the supply voltage and generates an interrupt if it
falls below a programmable threshold level.
Wake-Up Timer
The wake-up timer has very low current consumption (1.5 uA typical) and can be programmed from
1 ms to several days with an accuracy of ±5%.
It calibrates itself to the crystal oscillator at every startup, and then every 30 seconds. When the
oscillator is switched off, the calibration circuit switches on the crystal oscillator only long enough for a
quick calibration (a few milliseconds) to facilitate accurate wake-up timing.
Event Handling
In order to minimize current consumption, the device supports sleep mode. Active mode can be
initiated by several wake-up events: timeout of wake-up timer, detection of low supply voltage or through
the serial interface.
If any wake-up event occurs, the wake-up logic generates an interrupt, which can be used to wake
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