Data Sheet

ADCA5190

APPLICATIONS INFORMATION

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Rev. 0 | 19 of 22

DOWNSTREAM APPLICATIONS CIRCUIT WITH

ACTIVE BIASING

The schematic in Figure 32 and the PCB layout in Figure 33

are recommended for downstream cable system applications from

45 MHz to 1800 MHz that employ active biasing. Recommended

values for all components are in the BOM listed in Downstream

Cable Application Circuit with Active Biasing Bill of Materials. The

RF transformer configured to transform the single-ended 75 Ω RF

input to a differential signal that drives the 37.5 Ω inputs of the

ADCA5190 (RFIN and RFIP). The active bias circuit comprises the

C19, C31, C32, Q1, R2, R11, R12, R13, and R15 components.

The circuit is connected to Pin 1 of E1. See Supply Voltage and

this circuit. C6 stabilizes the output of the active bias circuit and

serves as the ac ground for the RF input signal. Capacitor C29

between the FBN pins (Pin 14 and Pin 16) provides feedback for

the negative side of the amplifier, and Capacitor C30 between the

FBP pins (Pin 25 and Pin 27) provides feedback for the positive

side of the amplifier.

T2 is an RF transformer configured to transform the differential 37.5

Ω outputs (RFON and RFOP) to a single-ended 75 Ω RF output.

The C3, C5, C7, C8, C13, C14, C18, C20 L8, L9, L10, and

L11 components are intended for impedance matching, and these

components must be optimized to match the RF input source and

RF output load. Capacitor C4 blocks the dc voltage of the RF input

source. Capacitor C27 and Capacitor C28 block the dc voltage at

the RFOP (Pin 22 and Pin 23) and RFON (Pin 18 and Pin 19)

output pins. The L2 and L3 inductors are RF chokes connected to

Figure 32. Suggested Downstream CATV Application Circuit with Active Biasing Schematic