RFM26W Datasheet, PDF (24/34 Pages) List of Unclassifed Manufacturers – ISM Transceiver module

RFM26W
5. Internal Functional Blocks
The following sections provide an overview to the key internal blocks and features.
5.1. RX Chain
The internal low-noise amplifier (LNA) is designed to be a wide-band LNA that can be matched with three external
discrete components to cover any common range of frequencies in the sub-GHz band. The LNA has extremely low
noise to suppress the noise of the following stages to achieve optimal sensitivity so no external gain or front-end
modules are necessary. The LNA has gain control which is controlled by the internal automatic gain control (AGC)
algorithm. The LNA is followed by an I-Q mixer, filter, programmable gain amplifier (PGA), and ADC. The I-Q
mixers downconvert the signal to an intermediate frequency. The PGA then boosts the gain to be within dynamic
range of the ADC. The ADC rejects out of band blockers and converts the signal to the digital domain where
filtering, demodulation, and processing is performed. Peak detectors are integrated at the output of the LNA and
PGA for use in the AGC algorithm.
5.2. RX Modem
Using high-performance ADCs allows channel filtering, image rejection, and demodulation to be performed in the
digital domain which allows for large amounts of flexibility to optimize the device for a particular application. The
digital modem performs the following functions:
Channel selection filter
TX modulation
RX demodulation
Automatic Gain Control (AGC)
Preamble detection
Invalid preamble detection
Radio signal strength indicator (RSSI)
Automatic frequency compensation (AFC)
Packet handling including EZMAC® features
Cyclic redundancy check (CRC)
The digital channel filter and demodulator are optimized for ultra low power consumption and are highly
configurable. Supported modulation types are GFSK, FSK, 4GFSK, 4FSK, ASK, and OOK. The channel filter can
be configured to support bandwidths ranging from 850 down to 1.1 kHz. A large variety of data rates are
supported ranging from 0.123 up to 1 Mbps. The configurable preamble detector is used to improve the reliability
of the sync-word detection. The sync-word detector is only enabled when a valid preamble is detected,
significantly reducing the probability of false detection. The received signal strength indicator (RSSI) provides a
measure of the signal strength received on the tuned channel. The resolution of the RSSI is 0.5 dB. This high
resolution RSSI enables accurate channel power measurements for clear channel assessment (CCA), carrier
sense (CS), and listen before talk (LBT) functionality. 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. The digital modem includes the TX
modulator which converts the TX data bits into the corresponding stream of digital modulation values to be
summed with the fractional input to the sigma-delta modulator. This modulation approach results in highly
accurate resolution of the frequency deviation. A Gaussian filter is implemented to support GFSK and 4GFSK,
considerably reducing the energy in the adjacent channels. The default bandwidth-time product (BT) is 0.5 for all
programmed data rates, but it may be adjusted to other values.
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