Evaluates: MAX9995
MAX9995 Evaluation Kit
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5
Layout Considerations
The MAX9995 evaluation board can be a guide for your
board layout. Pay close attention to thermal design and
close placement of parts to the IC. The package’s
exposed paddle (EP) conducts heat from the part and
provides a low-impedance electrical connection. The
EP
MUST
be attached to the PC board ground plane
with a low thermal and electrical impedance contact.
Ideally, this can be achieved by soldering the backside
package contact directly to a top metal ground plane
on the PC board. Alternatively, the EP can be connect-
ed to a ground plane using an array of plated vias
directly below the EP. The EV kit uses nine evenly
spaced, 0.016in-diameter, plated through holes to con-
nect the EP to the lower ground planes.
Depending on the RF ground-plane spacing, large sur-
face-mount pads in the RF path may need the ground
plane relieved under them to reduce shunt capacitance.
Modifying the EV Kit
The RF and LO inputs are broadband matched, so
there is no need to modify the circuit for use anywhere
in the 1700MHz to 2200MHz RF range (1400MHz to
2000MHz LO range).
Retuning for a different IF frequency is as simple as
scaling the values of the IF pullup inductors up or down
with frequency. The IF output looks like 200
Ω
differen-
tial in parallel with a capacitor. The capacitance is due
to the combination of the IC, PC board, and external IF
components. The capacitance from the IC is approxi-
mately 2pF to ground (1pF differential), while that from
the PC board and external components is approxi-
mately 3.5pF to ground. The total 5.5pF of capacitance
is resonated out at the frequency of interest by the bias
inductors. To determine the inductor value, use the fol-
lowing equation:
The IF output is tuned for operation at approximately
200MHz, so a 330nH inductor is used. For lower IF fre-
quencies (i.e., larger component values), maintain the
component’s Q value at the cost of larger case size,
unless it is unavoidable.
f
L x C
IF
=
1
2
π