ADA4303-2

Rev. 0 | Page 8 of 12

APPLICATIONS

The ADA4303-2 active splitter is primarily intended for use

in the downstream path of television set-top boxes (STBs) that

contain multiple tuners. It is typically located directly after the

diplexer in a CATV customer premise unit. The ADA4303-2

provides a single-ended input and two single-ended outputs

that allow the delivery of the RF signal to two different signal

paths. These paths can include, but are not limited to, a main

picture tuner, a picture-in-picture (PIP) tuner, an out-of-band

(OOB) tuner, a digital video recorder (DVR), and a cable

modem (CM).

The ADA4303-2 exhibits composite second-order (CSO) and

composite triple beat (CTB) products that are −62 dBc and

−72 dBc, respectively. The use of the SiGe process also allows

the ADA4303-2 to achieve a noise figure (NF) of less than 4.5 dB.

CIRCUIT DESCRIPTION

The ADA4303-2 consists of a low noise buffer amplifier followed

by a resistive power divider. This arrangement provides 3 dB of

gain relative to the RF signal present at the input of the device.

The input and each output must be properly matched to a 75 Ω

environment for distortion and noise performance to match the

data sheet specifications. In addition, to achieve the specified gain,

a 1% 249 Ω resistor should be installed to ground on each output.

AC coupling capacitors of 0.01 μF are recommended for the

input and outputs.

A 1 μH RF choke (Coilcraft chip inductor 0805LS-102X) is

required to correctly bias internal nodes of the ADA4303-2.

It should be connected between the 5 V supply and IL (Pin 11).

EVALUATION BOARD

The ADA4303-2 evaluation board allows designers to assess the

performance of the part in their particular applications. The board

includes 75 Ω coaxial connectors and 75 Ω controlled-impedance

signal traces that carry the input and output signals. Power (5 V)

is applied to the red VCC loop connector, and ground is connected

to the black GND loop connector.

The board has two 249 Ω resistors between each output and

ground that set the gain of the overall circuit to 3 dB and

improve output-to-output isolation. A schematic of the

ADA4303-2 evaluation board is shown in Figure 17.

RF LAYOUT CONSIDERATIONS

Appropriate impedance matching techniques are mandatory

when designing a circuit board for the ADA4303-2. Improper

characteristic impedances on traces can cause reflections that

can lead to poor linearity. The characteristic impedance of the

signal trace from each output should be 75 Ω.

POWER SUPPLY

The 5 V supply should be applied to each of the VCC pins and

RF choke via a low impedance power bus. The power bus should

be decoupled to ground using a 10 μF tantalum capacitor and

a 0.1 μF ceramic chip capacitor located close to the ADA4303-2.

In addition, the VCC pins should be decoupled to ground with

a 0.1 μF ceramic chip capacitor located as close to each of the

pins as possible.

1

ADA4303-2

C3

0.01μF

249Ω

L1

1.0μH

VCC

GND

VCC

VIN

2

3

45

7

9

6

8

10

11

12

J3

J2

J1

GND

GND

NC = NO CONNECT

VO2

VO1

C2

0.01μF

C4

0.01μF

C5

10µF

+

C6

0.1µF

C1

0.1µF

249Ω

Figure 17. ADA4303-2 Evaluation Board Schematic