CC2420 Datasheet, PDF (16/87 Pages) List of Unclassifed Manufacturers – 2.4 GHz IEEE 802.15.4 / ZigBee-ready RF Transceiver

SmartRF ^® CC2420
Circuit Description
LNA
TX/RX CONTROL
SmartRF ^®
CC2420
Power
Control
PA
Σ
On-chip
BIAS
XOSC
R
16 MHz
AUTOMATIC GAIN CONTROL
ADC
ADC
DIGITAL
DEMODULATOR
- Digital RSSI
- Gain Control
- Image Suppression
- Channel Filtering
- Demodulation
- Frame
synchronization
Serial
voltage
regulator
0
90
FREQ
SYNTH
TX POWER CONTROL
DIGITAL
INTERFACE
WITH FIFO
BUFFERS,
CRC AND
ENCRYPTION
DAC
DAC
DIGITAL
MODULATOR
- Data spreading
- Modulation
Digital and
Analog test
interface
Figure 2. CC2420 simplified block diagram
A simplified block diagram of CC2420 is
shown in Figure 2.
CC2420 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
synchronisation are performed digitally.
When the SFD pin goes high, this indicates
that a start of frame delimiter has been
detected. CC2420 buffers the received data
in a 128 byte receive FIFO. The user may
read the FIFO through an 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 modes are
also available for test purposes.
The CC2420 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 delimiter are generated by
hardware. Each symbol (4 bits) is spread
using the IEEE 802.15.4 spreading
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 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
connecting TXRX_SWITCH to RF_P and
RF_N through an external DC path.
The frequency synthesizer includes a
completely on-chip LC VCO and a 90
Chipcon AS SmartRF^® CC2420 Preliminary Datasheet (rev 1.2), 2004-06-09
Page 16 of 87