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26. System Considerations and Guidelines
26.1 SRD regulations
International regulations and national laws
regulate the use of radio receivers and
transmitters. SRDs (Short Range Devices)
for licence free operation are allowed to
operate in the 433 and 868-870 MHz
bands in most European countries. In the
United States such devices operate in the
260–470 and 902-928 MHz bands.
is designed to meet the requirements for
operation in all these bands. A summary
of the most important aspects of these
regulations can be found in Application
Note AN001 SRD regulations for licence
free transceiver operation, available from
Chipcon's web site.
26.2 Low cost systems
In systems where low cost is of great
CC1000
importance the
Very few external components keep the
total cost at a minimum. The oscillator
crystal can then be a low cost crystal with
50 ppm frequency tolerance.
26.3 Battery operated systems
In low power applications the power down
mode should be used when not being
active. Depending on the start-up time
requirement, the oscillator core can be
powered during power down. See page 28
for information on how effective power
management can be implemented.
26.4 Crystal drift compensation
CC1000
A unique feature in
frequency resolution of 250 Hz. This can
be
used
to
do
compensation
of
the
temperature drift curve is known and a
temperature sensor is included in the
system. Even initial adjustment can be
done using the frequency programmability.
This eliminates the need for an expensive
CC1000
is the ideal choice.
is the very fine
the
temperature
crystal
if
the
SWRS048A
TCXO and trimming in some applications.
In less demanding applications a crystal
with low temperature drift and low ageing
could
be
used
compensation. A trimmer capacitor in the
crystal oscillator circuit (in parallel with
C171) could be used to set the initial
frequency accurately. The fine frequency
step programming cannot be used in RX
mode if optimised frequency settings are
required (see page 24).
26.5 High reliability systems
Using a SAW filter as a preselector will
improve the communication reliability in
harsh environments by reducing the
probability
of
blocking.
sensitivity and the output power will be
reduced due to the filter insertion loss. By
inserting the filter in the RX path only,
together with an external RX/TX switch,
only the receiver sensitivity is reduced,
and output power is remained. The
CHP_OUT (LOCK) pin can be configured
to control an external LNA, RX/TX switch
or power amplifier. This is controlled by
LOCK_SELECT in the LOCK register.
26.6 Frequency hopping spread
spectrum systems
Due to the very fast frequency shift
properties of the PLL, the
suitable for frequency hopping systems.
Hop rates of 1-100 hops/s are usually
used depending on the bit rate and the
amount of data to be sent during each
transmission. The two frequency registers
(FREQ_A and FREQ_B) are designed
such that the 'next' frequency can be
programmed while the 'present' frequency
is used. The switching between the two
frequencies is done through the MAIN
register.
CC1000
without
further
The
receiver
CC1000
is also
Page 37 of 55
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