EM2420 ETC [List of Unclassifed Manufacturers], EM2420 Datasheet - Page 16

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

Circuit Description
Figure 2. The EM2420 simplified block diagram
A simplified block diagram of the EM2420 is
shown in Figure 2.
The EM2420 features a low-IF receiver.
The received RF signal is amplified by the
low-noise amplifier (LNA) and down-
converted in quadrature (I and Q) to the
intermediate frequency (IF). At IF (2 MHz),
the complex I/Q signal is filtered and
amplified, and then digitized by the ADCs.
Automatic gain control, final channel
filtering, de-spreading, symbol correlation
and byte synchronization are performed
digitally.
When the SFD pin goes high, this indicates
that a start of frame delimiter has been
detected. The EM2420 buffers the received
data in a 128 byte receive FIFO. The user
may read the FIFO through a SPI
interface. CRC is verified in hardware.
RSSI and correlation values are appended
to the frame. CCA is available on a pin in
receive mode. Serial (unbuffered) data
Ember Part Number: 120-0049-000C
EM2420 Datasheet
modes
purposes.
The EM2420 transmitter is based on direct
up-conversion. The data is buffered in a
128 byte transmit FIFO (separate from the
receive FIFO). The preamble and start of
frame
hardware. Each symbol (4 bits) is spread
using
sequence to 32 chips and output to the
digital-to-analog converters (DACs).
An analog lowpass filter passes the signal
to the quadrature (I and Q) upconversion
mixers. The RF signal is amplified in the
power amplifier (PA) and fed to the
antenna.
The internal T/R switch circuitry makes the
antenna interface and matching very easy.
The RF connection is differential. A balun
may be used for single-ended antennas.
The biasing of the PA and LNA is done by
the
delimiter
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IEEE
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802.15.4
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EM2420
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Page 16 of 89
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