ADA4302-4

Rev. B | Page 8 of 12

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).

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.

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.

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.

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.

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).

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.

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.