Data Sheet

ADCA3280

APPLICATIONS INFORMATION

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Rev. 0 | 15 of 18

RECOMMENDED APPLICATIONS CIRCUIT AND

BOM

The schematic in Figure 24 is recommended for downstream cable

system applications from 108 MHz to 1794 MHz, for both DOCSIS

3.1 and DOCSIS 4.0. Recommended values for all components

are in the BOM listed in Table 8. T1 and T2 are RF transformers

configured to transform the single-ended 75 Ω RF input and output

to differential signals that drive the 37.5 Ω inputs and outputs of the

ADCA3280 (RFIN, RFIP, RFON, and RFOP).

The C1, C2, C4, C7, C8, C9, C10, C14, C15, C16, C17, and

R1 components are intended for impedance matching, and these

components must be optimized to match the RF input source and

RF output load. Capacitors C1, C9, and C10 also serve as DC

blocks for the RF input and output pins. Inductors L2 and L3 are RF

chokes connected to the filtered VDD supply voltage. Components

C11, C12, C13, C18, C19, C20, C21, C22, C23, L1, E2, and E3

are present to filter the DC supply lines. If these lines are otherwise

filtered in the application, then some or all of these components

may not be necessary.

The network connected to the IADJ pin (Pin 2) sets up a voltage to

control the bias current of the amplifier. The RT1 component trims

the adjustment voltage as a function of temperature and provides

more stable bias current over temperature. Expect bias current to

vary ±15 mA over temperature extremes from a nominal set point.

If bias adjustment is not required for the application, R5, C19, and

the IADJ net can be removed, and the ADCA3280 is passively set

to a nominal current by R3 and RT1. Adjustment of the bias current

via IADJ is discussed in detail in the Supply Voltage and Current

section.

When laying out a circuit for the ADCA3280, it is recommended

to follow the layout for the evaluation board shown in the EVAL-AD-

CA3280 User Guide. Particularly important are the relative distan-

ces between the ADCA3280 and T1, T2, as well as the tuning

components in between those components (C4, C7, C8, and C14).

Figure 24. Recommended Application Circuit Schematic