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ADA4303-2 Datasheet(PDF) 8 Page - Analog Devices |
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ADA4303-2 Datasheet(HTML) 8 Page - Analog Devices |
8 / 12 page 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 |
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