CC2420 Chipcon AS, CC2420 Datasheet - Page 52

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

Input / Output Matching
The RF input / output is differential (RF_N
and RF_P). In addition there is supply
switch output pin (TXRX_SWITCH) that
must have an external DC path to RF_N
and RF_P.
In RX mode the TXRX_SWITCH pin is at
ground and will bias the LNA. In TX mode
the TXRX_SWITCH pin is at supply rail
voltage and will properly bias the internal
PA.
The RF output and DC bias can be done
using different topologies. Some are
shown in Figure 3 and Figure 4.
Component values are given in Table 2.
Using a differential antenna, no balun is
required.
Transmitter Test Modes
CC2420
test modes for performance evaluation.
The test mode descriptions in the following
sections requires that the chip is first
reset, the crystal oscillator is enabled
using the SXOSCON command strobe and
that the crystal oscillator has stabilised.
Unmodulated carrier
An
transmitted
MDMCTRL1.TX_MODE to 2, writing 0x1800
Chipcon AS SmartRF ® CC2420 Preliminary Datasheet (rev 1.0), 2003-11-17
unmodulated
can be set into different transmit
by
carrier
may
setting
be
SmartRF
If a single ended output is required (for a
single ended connector or a single ended
antenna), a balun should be used for
optimum performance. The balun can be
realized using discrete inductors and
capacitors, or a LTCC balun can be used.
If the power amplifier is configured for
single ended use, then a simpler matching
network can be used. The output power
and sensitivity will however be reduced.
The RF_N pin should then be terminated in
a grounded capacitor and the RF_P pin
should
TXRX_SWITCH pin.
to the DACTST
STXON command strobe. The transmitter
is then enabled while the transmitter I/Q
DACs are overridden to static values. An
unmodulated carrier will then be available
on the RF output pins.
A plot of the single carrier output spectrum
from
CC2420
have
is shown in Figure 29 below.
a
®
register and issue a
DC
CC2420
path
Page 52 of 85
to
the