CC1100 Datasheet, PDF (23/70 Pages) List of Unclassifed Manufacturers – CC1100 Single Chip Low Cost Low Power RF-Transceiver

Chipcon
SmartRF ^® CC1100
The CC1100 supports channel filter bandwidths
between 54-63kHz and 600-700kHz¹. Above
300kHz bandwidth, however, the sensitivity
and blocking performance may be somewhat
degraded.
For best performance, the channel filter
bandwidth should be selected so that the
signal bandwidth occupies at most 80% of the
channel filter bandwidth. The channel centre
1 _{The combination of CHANBW_E=0 and}
CHANBW_M=0 is not supported. Exact limits
depend on crystal frequency.
tolerance due to crystal accuracy should also
be subtracted from the signal bandwidth. The
following example illustrates this:
With the channel filter bandwidth set to
500kHz, the signal should stay within 80% of
500kHz, which is 400kHz. Assuming 915MHz
frequency and ±20ppm frequency uncertainty
for both the transmitting device and the
receiving device, the total frequency
uncertainty is ±40ppm of 915MHz, which is
±37kHz. If the whole transmitted signal
bandwidth is to be received within 400kHz, the
transmitted signal bandwidth should be
maximum 400kHz–2·37kHz, which is 326kHz.
22 Demodulator, Symbol Synchronizer and Data Decision
CC1100 contains an advanced and highly
configurable demodulator. Channel filtering
and frequency offset compensation is
performed digitally. To generate the RSSI level
(see section 25.2 for more information) the
signal level in the channel is estimated. Data
filtering is also included for enhanced
performance.
22.1 Frequency Offset Compensation
When using 2-FSK, GFSK or MSK modulation,
the demodulator will compensate for the offset
between the transmitter and receiver
frequency, within certain limits, by estimating
the centre of the received data. This value is
available in the FREQEST status register.
should be issued when currently receiving a
packet, or outside the RX state.
Note that frequency offset compensation is not
supported for ASK or OOK modulation.
22.2 Bit Synchronization
The bit synchronization algorithm extracts the
clock from the incoming symbols. The
algorithm requires that the expected data rate
is programmed as described in Section 20 on
page 22. Re-synchronization is performed
continuously to adjust for error in the incoming
symbol rate.
22.3 Byte synchronization
By issuing the SAFC command strobe, the
measured offset, FREQEST.FREQOFF_EST,
can automatically be used to adjust the
frequency offset programming in the frequency
synthesizer. This will add the current RX
frequency offset estimate to the value in
FSCTRL0.FREQOFF, which adjust the
synthesizer frequency. Thus, the frequency
offset will be compensated in both RX and TX
when the SAFC command strobe is used.
To avoid compensating for frequency offsets
measured without a valid signal in the RF
channel, FREQEST.FREQOFF_EST is copied
to an internal register when issuing the SAFC
strobe in RX, and when a synch word is
detected. If SAFC was issued in RX, this
internal value is added to FSCTRL0.FREQOFF
after exiting RX. Issuing SAFC when not in RX
will immediately add the internal register value
to FSCTRL0.FREQOFF. Thus, the SAFC strobe
Byte synchronization is achieved by a
continuous sync word search. The sync word
is a 16 or 32 bit configurable field that is
automatically inserted at the start of the packet
by the modulator in transmit mode. The
demodulator uses this field to find the byte
boundaries in the stream of bits. The sync
word will also function as a system identifier,
since only packets with the correct predefined
sync word will be received. The sync word
detector correlates against the user-configured
16-bit sync word. The correlation threshold
can be set to 15/16 bits match or 16/16 bits
match. The sync word can be further qualified
using the preamble quality indicator
mechanism described below and/or a carrier
sense condition. The sync word is
programmed with SYNC1 and SYNC0.
In order to make false detections of sync
words less likely, a mechanism called
preamble quality indication (PQI) can be used
Chipcon AS
SmartRF^® CC1100 Preliminary Data Sheet (rev. 1.0) 2005-04-25
Page 23 of 68