SWRS046H – NOVEMBER 2006 – REVISED MARCH 2015
A unique feature in CC1020 is the very fine frequency resolution. This can be used for temperature
compensation of the crystal if the temperature drift curve is known and a temperature sensor is included in
the system. Even initial adjustment can be performed using the frequency programmability. This
eliminates the need for an expensive TCXO and trimming in some applications. For more details refer to
AN027 Temperature Compensation by Indirect Method
).
In less demanding applications, a crystal with low temperature drift and low aging could be used without
further compensation. A trimmer capacitor in the crystal oscillator circuit (in parallel with C5) could be used
to set the initial frequency accurately.
The frequency offset between a transmitter and receiver is measured in the CC1020 and can be read
back from the AFC register. The measured frequency offset can be used to calibrate the receiver
frequency using the transmitter as the reference. For more details refer to
AN029 CC1020/1021 Automatic
Frequency Control (AFC)
(
CC1020 also has the possibility to use Gaussian shaped FSK (GFSK). This spectrum-shaping feature
improves adjacent channel power (ACP) and occupied bandwidth. In ‘true’ FSK systems with abrupt
frequency shifting, the spectrum is inherently broad. By making the frequency shift ‘softer’, the spectrum
can be made significantly narrower. Thus, higher data rates can be transmitted in the same bandwidth
using GFSK.
5.20.3 Low Cost Systems
As the CC1020 provides true narrowband multi-channel performance without any external filters, a very
low cost high performance system can be achieved. The oscillator crystal can then be a low cost crystal
with 50 ppm frequency tolerance using the on-chip frequency tuning possibilities.
5.20.4 Battery Operated Systems
In low power applications, the power down mode should be used when CC1020 is not being active.
Depending on the start-up time requirement, the oscillator core can be powered during power down. See
for information on how effective power management can be implemented.
5.20.5 High Reliability Systems
Using a SAW filter as a preselector will improve the communication reliability in harsh environments by
reducing the probability of blocking. The receiver 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 PA_EN and LNA_EN pin can
be configured to control an external LNA, RX/TX switch or power amplifier. This is controlled by the
INTERFACE register.
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Detailed Description
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