ADA4304-2(Rev0) Ver la hoja de datos (PDF) - Analog Devices
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ADA4304-2 Datasheet PDF : 12 Pages
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ADA4304-2
APPLICATIONS
The ADA4304-2 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 bidirectional CATV customer premise unit. The
ADA4304-2 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, the picture-in-picture (PIP)
tuner, an out-of-band (OOB) tuner, a digital video recorder
(DVR), and a cable modem (CM).
The ADA4304-2 exhibits composite second order (CSO) and
composite triple beat (CTB) products that are −62 dBc and
−72 dBc, respectively. The use of the SiGe bipolar process also
allows the ADA4304-2 to achieve a noise figure (NF) of 4 dB.
CIRCUIT DESCRIPTION
The ADA4304-2 consists of a low noise buffer amplifier followed
by a resistive power divider. This arrangement provides 2.8 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. 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 ADA4304-2. It
should be connected between the 5 V supply and the IL pin
(Pin 14). The choke should be placed as close as possible to
the ADA4304-2 to minimize parasitic capacitance on the
IL pin, which is critical for achieving the specified bandwidth
and flatness.
EVALUATION BOARDS
The ADA4304-2 evaluation board allows designers to assess the
performance of the parts in their particular application. 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. Figure 20 is
a schematic of the ADA4304-2 evaluation board. On the
ADA4304-2 evaluation board, connectors VO1 and VO4 are
not populated.
RF LAYOUT CONSIDERATIONS
Appropriate impedance matching techniques are mandatory
when designing circuit boards for the ADA4304-2. Improper
characteristic impedances on traces can cause reflections that
can lead to poor linearity. The characteristic impedance of the
signal trace to the input and from each output should be 75 Ω.
Any ground metal on the top surface near signal lines should be
stitched with vias to the internal ground plane, as shown in
Figure 21.
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 ADA4304-2. 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.
GND
VCC
C5 +
10µF
L1
1.0μH
C1
0.1µF
C8
0.1µF
C2
VIN
0.01μF
16 15 14 13
1 VCC
12
VOUT1
C3
0.01μF
VO2
2
3
11
VCC ADA4304-2 GND 10
GND
VOUT2
C4
0.01μF
VO3
4
VIN
9
GND
5 6 78
NC = NO CONNECT
Figure 20. Evaluation Board Schematic
Rev. 0 | Page 9 of 12
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