ADA4302-4
APPLICATIONS
The ADA4302-4 active splitter is primarily intended for use in
the downstream path of television set-top boxes (STBs) that
contain multiple tuners. It is located directly after the diplexer
in a CATV customer premise unit. The ADA4302-4 provides a
differential input and four differential outputs that allow the
delivery of the RF signal to up to four different signal paths.
These paths can include, but are not limited to, a main picture
tuner, the picture-in-picture (PIP) tuner, a digital video
recorder (DVR), and a cable modem (CM).
EVALUATION BOARDS
There are two evaluation boards for the ADA4302-4, a single-
ended output board (ADA4302-4 EBSE) and a differential
output board (ADA4302-4 EBDI). The single-ended output
board has an input balun that converts a signal from a single-
ended source to a differential signal. The differential output
board uses the same input balun and allows the output signals
to run directly to the board connectors. This allows the
differential signals at the ADA4302-4’s outputs to be applied
directly to a tuner with differential inputs. The schematics for
these evaluation boards can be seen in Figure 16 and Figure 17,
respectively.
The differential nature of the ADA4302-4 allows it to provide
composite second-order (CSO) and composite triple beat
(CTB) products that are −73 dBc and −66 dBc, respectively. The
use of the SiGe process also allows the ADA4302-4 to achieve a
noise figure (NF) that is less than 5 dB.
Each board has place holders to properly terminate the unused
outputs, if needed. On the single-ended output board, they are
designated R15 through R18, and 75 Ω resistors should be used
here (see Figure 16). On the differential output board, 37.5 Ω
resistors should be used for R1, R2, and R4 through R9 when
their respective outputs are not in use (see Figure 17).
CIRCUIT DESCRIPTION
The ADA4302-4 has a low noise buffer amplifier that is
followed by four parallel amplifiers. This arrangement
provides 4.6 dB of gain relative to the RF signal present at the
differential inputs of the active splitter. The input and each
output must be properly matched to a differential 75 Ω
environment in order for distortion and noise performance
to match the data sheet specifications. If needed, baluns to
convert to single-ended operation can be used. The M/A-COM
MABAES0029 is recommended for the input balun and the
Mini-Circuit® TC1-1-13M-2 is recommended for the output
balun. AC coupling capacitors of 0.01 μF are recommended for
all inputs and outputs.
RF LAYOUT CONSIDERATIONS
Appropriate impedance matching techniques are mandatory
when designing a circuit board for the ADA4302-4. Improper
characteristic impedances on traces can cause reflections that
can lead to poor linearity. If the stage following the ADA4302-4
is a single-ended load with a 75 Ω impedance, then a balun
should be used. The characteristic impedance of the signal
trace from each output of a differential pair to the output
balun should be 37.5 Ω. In the case of the differential output
evaluation board, the output traces should also have a
characteristic impedance of 37.5 Ω.
Two 1 μH RF chokes, L1 and L2 (Coilcraft chip inductor
0805LS-102X), are used to correctly bias internal nodes of the
ADA4302-4 by connecting them between the 5 V supply and
ILN and ILP, respectively.
POWER SUPPLY
The 5 V supply should be applied to each of the VCC pins and
RF chokes via a low impedance power bus. The power bus
should be decoupled to ground using a 10 μF tantalum
capacitor and a 0.01 μF ceramic chip capacitor located close to
the ADA4302-4. In addition, the VCC pins should be decoupled
to ground with a 0.01 μF ceramic chip capacitor located as close
to each of the pins as possible. Pin 3 and Pin 4 can share one
capacitor, and Pin 12 and Pin 13 can share one capacitor.
Rev. B | Page 8 of 12
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