EM2420 ETC [List of Unclassifed Manufacturers], EM2420 Datasheet - Page 59

• Manufacturer Part Number: EM2420
• Description: 2.4 GHz IEEE 802.15.4 / ZigBee RF Transceiver
• Manufacturer: ETC [List of Unclassifed Manufacturers]

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. The EM2420 uses direct
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 the EM2420 it is also possible to
combine both DSSS and FHSS (frequency
hopping spread spectrum) in a proprietary
non-IEEE
achieved by reprogramming the operating
frequency
Channel Programming section on page
51) before enabling RX or TX. A frequency
synchronization 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 the EM2420 lets the
user 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 the EM2420
also
consumption compared to the 868 / 915
MHz bands defined by [1], where only 20 /
40 kbps are available. The EM2420 may be
powered up a smaller portion of the time,
so that the average power consumption is
Ember Part Number: 120-0049-000C
reduces
802.15.4
(see
the
the
system.
average
Frequency
This
power
and
EM2420 Datasheet
is
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 the EM2420 allows
up to 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
The EM2420 provides very good adjacent,
alternate and co channel rejection, image
frequency
properties. The EM2420 performance is
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 operations in the EM2420
enable secure communication, which is
required for many applications. Security
operations require a lot of data processing
which is costly in an 8-bit microcontroller
system. The hardware support within the
hardware
suppression
encryption
EM2420
and
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