7

component. Likewise for RX2. The 75

Ω back terminating

resistor RXT is recommended when driving 75

Ω cables.

The board layout should have a ground plane underneath

the EL4089, with the ground plane cut away from the vicinity

capacitance on pin 1.

Power supply bypassing is important, and a 0.1µF ceramic

capacitor, from each power pin to ground, placed very close

to the power pins, together with a 4.7µF tantalum bead

capacitor, is recommended.

When both digital and analog grounds are on the same

board, the EL4089 should be on the analog ground. The

digital ground can be connected to the Analog ground

through a 100

Ω-300Ω resistor, near the EL4089. This allows

the digital signal a return path, while preventing the digital

noise from corrupting the analog ground.

For best results the source impedance should be kept low,

using a buffer for example.

The S/H amplifier is current output and causes a small load

on the input source during sampling. When sampling is done

on the back porch with color burst there will be a small load

on the color burst. Therefore for best performance, the input

should be driven from an amplifier output or a 75

Ω cable with

75

Ω termination.

TABLE OF CHARGE STORAGE CAPACITOR VS DROOP

CHARGING RATES (NOTE)

CAP VALUE

nF

DROOP IN

60µs

mV

CHARGE IN

1.2µs

mV

CHARGE IN

4µs

mV

10

6

36

120

33

1.8

11

36

100

0.6

3.6

12

NOTE: Basic formulae are: V (droop) = Ib+ * (Line time - Sample

FIGURE 1.

EL4089