RFM31B Datasheet, PDF (26/63 Pages) List of Unclassifed Manufacturers – ISM RECEIVER

RFM31B
measurements for clear channel assessment (CCA), and carrier sense (CS) functionality.
Frequency mistuning caused by crystal inaccuracies can be compensated by enabling the digital automatic
frequency control (AFC) in receive mode.
A comprehensive programmable packet handler including key features of EZMac^TM is integrated to
create a variety of communication topologies ranging from peer-to-peer networks to mesh networks. The extensive
programmability of the packet header allows for advanced packet filtering which in turn enables a mix of broadcast,
group, and point-to-point communication.
A wireless communication channel can be corrupted by noise and interference, and it is therefore important to
know if the received data is free of errors. A cyclic redundancy check (CRC) is used to detect the presence of
erroneous bits in each packet. A CRC is computed and appended at the end of each transmitted packet and
verified by the receiver to confirm that no errors have occurred. The packet handler and CRC can significantly
reduce the load on the system microcontroller allowing for a simpler and cheaper microcontroller.
5.6. Synthesizer
An integrated Sigma Delta (ΣΔ) Fractional-N PLL synthesizer capable of operating from 240–960 MHz is provided
on-chip. Using a ΣΔ synthesizer has many advantages; it provides flexibility in choosing data rate, deviation,
channel frequency, and channel spacing.
The PLL and - modulator scheme is designed to support any desired frequency and channel spacing in the
range from 240–960 MHz with a frequency resolution of 156.25 Hz (Low band) or 312.5 Hz (High band).
Fref = 10 M
PFD
CP
LPF
Selectable
Divider
RX
VCO
N
Figure 9. PLL Synthesizer Block Diagram
The reference frequency to the PLL is 10 MHz. The PLL utilizes a differential L-C VCO, with integrated on-chip
inductors. The output of the VCO is followed by a configurable divider which will divide down the signal to the
desired output frequency band. The modulus of the variable divide-by-N divider stage is controlled dynamically by
the output from the - modulator. The tuning resolution is sufficient to tune to the commanded frequency with a
maximum accuracy of 312.5 Hz anywhere in the range between 240–960 MHz.
5.6.1. VCO
The output of the VCO is automatically divided down to the correct output frequency depending on the hbsel and
fb[4:0] fields in "Register 75h. Frequency Band Select." In receive mode, the LO frequency is automatically shifted
downwards by the IF frequency of 937.5 kHz, allowing receive operation on the same frequency. The VCO
integrates the resonator inductor and tuning varactor, so no external VCO components are required.
The VCO uses a capacitance bank to cover the wide frequency range specified. The capacitance bank will
automatically be calibrated every time the synthesizer is enabled. In certain fast hopping applications this might not
be desirable so the VCO calibration may be skipped by setting the appropriate register.
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