Rainbow Electronics RF01 - Manual (Page 3)

RF01
DETAILED DESCRIPTION
General
The RF01 FSK receiver is the counterpart of the Hope’s FSK transmitter. It covers the unlicensed
frequency bands at 315, 433, 868, and 915 MHz. The device facilitates compliance with FCC and ETSI
requirements.
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 for the use
of multiple channels in any of the bands.
The receiver employs the Zero-IF approach with I/Q demodulation, allowing the use of a minimal
number of external components in a typical application. The RF01 consists of a fully integrated
multi-band PLL synthesizer, an LNA with switchable gain, I/Q down converter mixers, baseband filters
and amplifiers, and an I/Q demodulator followed by a data filter.
The RF VCO in the PLL performs automatic calibration, which requires only a few microseconds.
Calibration always occurs when the synthesizer begins. If temperature or supply voltage changes
significantly, VCO recalibration can be invoked easily. Recalibration can be initiated at any time by
switching the synthesizer off and back on again.
LNA
The LNA has 250 Ohm input impedance, which works well with the recommended antennas.
If the RF input of the chip is connected to 50 Ohm devices, an external matching circuit is required to
provide the correct matching and to minimize the noise figure of the receiver.
The LNA gain (and linearity) can be selected (0, –6, –14, –20 dB relative to the highest gain)
according to RF signal strength. This is useful in an environment with strong interferers.
Baseband Filters
The receiver bandwidth is selectable
by programming the bandwidth (BW) of the
baseband filters. This allows setting up the
receiver according to the characteristics of
the signal to be received. An appropriate
bandwidth can be selected to
accommodate various FSK deviation, data
rate, and crystal tolerance requirements.
The filter structure is a 7-th order
Butterworth low-pass with 40 dB
suppression at 2*BW frequency. Offset
cancellation is accomplished by using a
high-pass filter with a cut-off frequency
below 7 kHz.
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