EM2420 ETC [List of Unclassifed Manufacturers], EM2420 Datasheet - Page 33

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

In receive mode, the FIFO pin can be
used to detect if there is data at all in the
receive FIFO.
The SFD pin can be used to extract the
timing information of transmitted and
received data frames. The SFD pin will go
high when a start of frame delimiter has
been completely detected / transmitted.
The
connected to a timer capture pin on the
microcontroller.
Demodulator, Symbol Synchronizer and Data Decision
The
demodulator is shown in Figure 14.
Channel filtering and frequency offset
compensation is performed digitally. The
signal level in the channel is estimated to
generate the RSSI level (see the RSSI /
Energy Detection section on page 48 for
more information). Data filtering is also
included for enhanced performance.
With the ±40 ppm frequency accuracy
requirement from [1], a compliant receiver
must be able to compensate for up to 80
ppm or 200 kHz. The EM2420 demodulator
tolerates up to 300 kHz offset without
significant degradation of the receiver
performance.
Soft decision is used at the chip level, i.e.
the demodulator does not make a decision
for each chip, only for each received
symbol. De-spreading is performed using
Figure 14. Demodulator Simplified Block Diagram
Frame Format
Ember Part Number: 120-0049-000C
I / Q Analog
IF signal
SFD
block
pin
diagram
ADC
should
for
preferably
the
IF Channel
Filtering
Digital
EM2420
EM2420 Datasheet
be
Compensation
Generator
Frequency
RSSI
Offset
For debug purposes, the SFD and CCA
pins can be used to monitor several status
signals as selected by the IOCFG1
register. See Table 12 for available
signals.
The polarity of FIFO, FIFOP, SFD and CCA
can be controlled by the IOCFG0 register
(address 0x1C).
over sampled symbol correlators. Symbol
synchronization
continuous start of frame delimiter (SFD)
search.
When a SFD is detected, data is written to
the RXFIFO and may be read out by the
microcontroller at a lower bit rate than the
250 kbps generated by the receiver.
The EM2420 demodulator also handles
symbol rate errors in excess of 120 ppm
without
Resynchronization
continuously to adjust for error in the
incoming symbol rate.
The MDMCTRL1.CORR_THR control bits
should be written to 20 to set the threshold
for detecting IEEE 802.15.4 start of frame
delimiters.
RSSI
Filtering
Digital
Data
performance
is
achieved
EM2420
Synchronisation
Correlators and
is
Symbol
degradation.
Value (may be
Page 33 of 89
used for LQI)
performed
Correlation
Average
by
Symbol
Output
a
Data