CC2420 Datasheet, PDF (18/87 Pages) List of Unclassifed Manufacturers – 2.4 GHz IEEE 802.15.4 / ZigBee-ready RF Transceiver

SmartRF ^® CC2420
Application Circuit
Few external components are required for
the operation of CC2420. A typical
application circuit is shown in Figure 3.
The external components are described in
Table 1 and typical values are given in
Table 2.
Input / output matching
The RF input/output is high impedance
and differential. The optimum differential
load for the RF port is 115+j180 Ω.
When using an unbalanced antenna such
as a monopole, a balun should be used in
order to optimise performance. The balun
can be implemented using low-cost
discrete inductors and capacitors. The
balun consists of C61, C62, C71, C81,
L61, L62 and L81, and will match the RF
input/output to 50 Ω, see Figure 3. L61
and L62 also provide DC biasing of the
LNA/PA input/output. An internal T/R
switch circuit is used to switch between
the LNA and the PA. See Input/output
matching section on page 53 for more
details.
If a balanced antenna such as a folded
dipole is used, the balun can be omitted. If
the antenna also provides a DC path from
TXRX_SWITCH pin to the RF pins,
inductors are not needed for DC bias.
Figure 4 shows a suggested application
circuit using a differential antenna. The
antenna type is a standard folded dipole.
The dipole has a virtual ground point;
hence bias is provided without
degradation in antenna performance.
A 27 nH series inductor may be connected
to the TXRX_SWITCH pin to improve the
transmitted EVM, but is not necessary to
comply with the requirements in [1].
Bias resistor
The bias resistor R451 is used to set an
accurate bias current.
Crystal
An external crystal with two loading
capacitors (C381 and C391) is used for
the crystal oscillator. See page 52 for
details.
Voltage regulator
The on chip voltage regulator supplies all
1.8 V power supply inputs. C42 is required
for stability of the regulator. A series
resistor may be used to comply with the
ESR requirement.
Power supply decoupling and filtering
Proper power supply decoupling must be
used for optimum performance. The
placement and size of the decoupling
capacitors and the power supply filtering
are very important to achieve the best
performance in an application. Chipcon
provides a compact reference design that
should be followed very closely.
Chipcon AS SmartRF^® CC2420 Preliminary Datasheet (rev 1.2), 2004-06-09
Page 18 of 87