ADF4360-3
Data Sheet
PCB DESIGN GUIDELINES FOR CHIP SCALE PACKAGE
Experiments have shown that the circuit shown in Figure 22
provides an excellent match to 50 Ω over the operating range of
the ADF4360-3. This gives approximately −2 dBm output
power across the frequency range of the ADF4360-3. Both
single-ended architectures can be examined using the EV-
ADF4360-3EB1Z evaluation board.
The leads on the chip scale package (CP-24) are rectangular.
The printed circuit board pad for these should be 0.1 mm
longer than the package lead length and 0.05 mm wider than
the package lead width. The lead should be centered on the pad
to ensure that the solder joint size is maximized.
V
VCO
The bottom of the chip scale package has a central thermal pad.
The thermal pad on the printed circuit board should be at least
as large as this exposed pad. On the printed circuit board, there
should be a clearance of at least 0.25 mm between the thermal
pad and the inner edges of the pad pattern to ensure that
shorting is avoided.
47nH
2.7pF
4.3nH
RF
OUT
50Ω
Figure 22. Optimum ADF4360-3 Output Stage
If the user does not need the differential outputs available on
the ADF4360, the user may either terminate the unused output
or combine both outputs using a balun. The circuit in Figure 23
shows how best to combine the outputs.
Thermal vias may be used on the printed circuit board thermal
pad to improve thermal performance of the package. If vias are
used, they should be incorporated in the thermal pad at a
1.2 mm pitch grid. The via diameter should be between 0.3 mm
and 0.33 mm, and the via barrel should be plated with 1 ounce
of copper to plug the via.
V
VCO
3.9nH
1.8pF
3.9nH
47nH
10pF
2.4nH
2.4nH
The user should connect the printed circuit thermal pad to
AGND. This is internally connected to AGND.
RF
RF
A
B
OUT
OUT
50Ω
OUTPUT MATCHING
There are a number of ways to match the output of the
ADF4360-3 for optimum operation; the most basic is to use a
50 Ω resistor to VVCO. A dc bypass capacitor of 100 pF is
connected in series, as shown Figure 21. Because the resistor is
not frequency dependent, this provides a good broadband
match. The output power in this circuit typically gives −3 dBm
output power into a 50 Ω load.
1.8pF
Figure 23. Balun for Combining ADF4360-3 RF Outputs
The circuit in Figure 23 is a lumped-lattice-type LC balun. It is
designed for a center frequency of 1.8 GHz and outputs 3.0 dBm
at this frequency. The series 2.4 nH inductor is used to tune out
any parasitic capacitance due to the board layout from each
input, and the remainder of the circuit is used to shift the
output of one RF input by +90° and the second by −90°, thus
combining the two. The action of the 3.9 nH inductor and the
1.8 pF capacitor accomplish this. The 47 nH is used to provide
an RF choke in order to feed the supply voltage, and the 10 pF
capacitor provides the necessary dc block. To ensure good RF
performance, the circuits in Figure 22 and Figure 23 were
implemented with Coilcraft 0402/0603 inductors and AVX 0402
thin-film capacitors.
V
VCO
51Ω
100pF
RF
OUT
50Ω
Figure 21. Simple ADF4360-3 Output Stage
A better solution is to use a shunt inductor (acting as an RF
choke) to VVCO. This gives a better match and therefore more
output power. Additionally, a series inductor is added after the
dc bypass capacitor to provide a resonant LC circuit. This tunes
the oscillator output and provides approximately 10 dB
additional rejection of the second harmonic. The shunt
inductor needs to be a relatively high value (>40 nH).
Alternatively, instead of the LC balun shown in Figure 23, both
outputs may be combined using a 180° rat-race coupler.
Rev. C | Page 22 of 24
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