CC2420 Chipcon AS, CC2420 Datasheet - Page 31

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

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 Synchroniser 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 45 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
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
Frame Format
CC2420
the IEEE 802.15.4 frame format. This
section gives a brief summary to the IEEE
Chipcon AS SmartRF ® CC2420 Preliminary Datasheet (rev 1.0), 2003-11-17
I / Q Analog
IF signal
SFD
block
has hardware support for parts of
pin
diagram
ADC
should
Figure 14. Demodulator Simplified Block Diagram
CC2420
for
preferably
the
demodulator
IF Channel
Filtering
Digital
CC2420
be
Compensation
Generator
Frequency
RSSI
Offset
SmartRF
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
synchronisation
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
symbol rate errors in excess of 120 ppm
without
Resynchronisation
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.
802.15.4 frame format, and describes how
CC2420
CC2420
is set up to comply with this.
RSSI
Filtering
Digital
Data
performance
demodulator also handles
®
is
achieved
CC2420
Synchronisation
Correlators and
is
Symbol
degradation.
Value (may be
Page 31 of 85
used for LQI)
performed
Correlation
Average
by
Symbol
Output
a
Data