CC2420 Chipcon AS, CC2420 Datasheet - Page 55

• Manufacturer Part Number: CC2420
• Description: 2.4 GHz RF Transceiver for IEEE 802.15.4 and ZigBee
• Manufacturer: Chipcon AS

System Considerations and Guidelines
SRD regulations
International regulations and national laws
regulate the use of radio receivers and
transmitters. SRDs (Short Range Devices)
for license free operation are allowed to
operate in the 2.4 GHz band worldwide.
The most important regulations are EN
300 440 (Europe), FCC CFR-47 part
15.247 and 15.249 (USA), and ARIB STD-
T-66 (Japan).
Frequency hopping and multi-channel
systems
The 2.4 GHz band is shared by many
systems both in industrial, office and home
environments.
sequence spread spectrum (DSSS) as
defined by [1] to spread the output power,
thereby making the communication link
more robust even in a noisy environment.
With
both DSSS and FHSS (frequency hopping
spread spectrum) in a proprietary non-
IEEE 802.15.4 system. This is achieved
by reprogramming the operating frequency
(see
Programming section on page 47) before
enabling
synchronisation scheme must then be
implemented within the proprietary MAC
layer to make the transmitter and receiver
operate on the same RF channel.
Data burst transmissions
The data buffering in
have a lower data rate link between the
microcontroller and the RF device than the
RF bit rate of 250 kbps. This allows the
microcontroller to buffer data at its own
speed, reducing the workload and timing
requirements.
The relatively high data rate of
also
consumption compared to the 868 / 915
MHz bands defined by [1], where only 20 /
40 kbps are available.
powered up a smaller portion of the time,
so that the average power consumption is
Chipcon AS SmartRF ® CC2420 Preliminary Datasheet (rev 1.0), 2003-11-17
CC2420
the
reduces
RX
it is also possible to combine
Frequency
or
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the
TX.
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average
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and
A
uses
lets the user
frequency
Channel
may be
CC2420
power
direct
SmartRF
reduced for a given amount of data to be
transferred.
Crystal accuracy and drift
A crystal accuracy of ±40 ppm is required
for compliance with IEEE 802.15.4 [1].
This accuracy must also take ageing and
temperature drift into consideration.
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 C7)
could be used to set the initial frequency
accurately.
For non-IEEE 802.15.4 systems, the
robust demodulator in
120 ppm total frequency offset between
the transmitter and receiver. This could
e.g. relax the accuracy requirement to 60
ppm for each of the devices.
Optionally in a star network topology, the
FFD could be equipped with a more
accurate crystal thereby relaxing the
requirement on the RFD. This can make
sense in systems where the RFDs ship in
higher volumes than the FFDs.
Communication robustness
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alternate and co channel rejection, image
frequency
properties. The
significantly better than the requirements
imposed by [1]. These are highly important
parameters for reliable operation in the 2.4
GHz band, since an increasing number of
devices/systems are using this license
free frequency band.
Communication security
The
authentication
enable secure communication, which is
required for many applications. Security
operations require a lot of data processing
which is costly in a 8-bit microcontroller
system. The hardware support within
hardware
provides very good adjacent,
suppression
operations
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®
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encryption
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performance is
and
allows up to
in
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blocking
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and