ax50424 AXSEM, ax50424 Datasheet - Page 22

• Manufacturer Part Number: ax50424
• Description: Advanced Multi-channel Single Chip Uhf Receiver
• Manufacturer: AXSEM

22
Circuit Description
Registers
Register
CICDECHI, CICDECLO
DATARATEHI, DATARATELO
TMGGAINHI, TMGGAINLO
MODULATION
FOURFSK, FSKDMAXHI,
FSKDMAXLO, FSKDMINHI,
FSKDMINLO
PHASEGAIN, FREQGAIN,
FREQGAIN2, AMPLGAIN
AGCATTACK, AGCDECAY
5.9.
The decoder is located between the Framing Unit and the Demodulator. It can optionally
transform the bit-stream in the following ways:
The decoder is programmed using the register ENCODING, details and recommendations on
usage are given in the
Version 1.3
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Decoder
It can invert the bit stream.
It can perform differential decoding. This means that a zero is transmitted as no
change in the level, and a one is transmitted as a change in the level. Differential
encoding is useful for PSK, because PSK transmissions can be received either as
transmitted or inverted, due to the uncertainty of the initial phase. Differential
encoding / decoding removes this uncertainty.
It can perform Manchester decoding. Manchester encoding ensures that the
modulation has no DC content and enough transitions (changes from 0 to 1 and from
1 to 0) for the demodulator bit timing recovery to function correctly, but does so at a
doubling of the data rate.
It can perform decoding of Spectral Shaping. Spectral Shaping removes DC content
of the bit stream, ensures transitions for the demodulator bit timing recovery, and
makes sure that the transmitted spectrum does not have discrete lines even if the
transmitted data is cyclic. It does so without adding additional bits, i.e. without
changing the data rate. Spectral Shaping uses a self synchronizing feedback shift
register.
AX50424
These registers program the bandwidth of the digital channel filter.
These registers specify the receiver bit rate, relative to the channel filter
bandwidth.
These registers specify the aggressiveness of the receiver bit timing recovery.
More aggressive settings allow the receiver to synchronize with shorter
preambles, at the expense of more timing jitter and thus a higher bit error rate
at a given signal-to-noise ratio.
This register selects the modulation to be used by the receiver, i.e. whether ASK,
PSK, FSK, MSK or OQPSK should be used.
These registers control the 4-FSK mode. Recommended settings and
procedures are provided in the Programming Manual.
These registers control the bandwidth of the phase, frequency offset and
amplitude tracking loops. Recommended settings are provided in the
Programming Manual.
These registers control the AGC (automatic gain control) loop slopes, and thus
the speed of gain adjustments. The faster the bit-rate, the faster the AGC loop
should be. Recommended settings are provided in the Programming Manual.
Programming Manual.
Remarks
Datasheet AX50424