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ADA4304-2ACPZ-R7 Datasheet(PDF) 9 Page - Analog Devices |
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ADA4304-2ACPZ-R7 Datasheet(HTML) 9 Page - Analog Devices |
9 / 12 page ADA4304-2 Rev. 0 | Page 9 of 12 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. ADA4304-2 L1 1.0μH GND VCC VO3 VIN NC = NO CONNECT C2 0.01μF C4 0.01μF VO2 C3 0.01μF C5 10µF + C1 0.1µF C8 0.1µF 1 VCC 2 VCC 3 GND 4 VIN 11 GND 12 VOUT1 10 VOUT2 9 GND 5 6 7 8 15 16 14 13 Figure 20. Evaluation Board Schematic |
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Similar Description - ADA4304-2ACPZ-R7 |
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