AD8065ART-R2 datasheet(21/28 Pages) AD

21 / 28 page

AD8065/AD8066

Rev. E | Page 21 of 28

LAYOUT, GROUNDING, AND BYPASSING CONSIDERATIONS

POWER SUPPLY BYPASSING

Power supply pins are actually inputs and care must be taken so

that a noise-free stable dc voltage is applied. The purpose of

bypass capacitors is to create low impedances from the supply

to ground at all frequencies, thereby shunting or filtering most

of the noise.

Decoupling schemes are designed to minimize the bypassing

impedance at all frequencies with a parallel combination of

capacitors. 0.1 µF (X7R or NPO) chip capacitors are critical

and should be as close as possible to the amplifier package.

The 4.7 µF tantalum capacitor is less critical for high frequency

bypassing, and, in most cases, only one is needed per board, at

the supply inputs.

GROUNDING

A ground plane layer is important in densely packed PC boards

to spread the current minimizing parasitic inductances.

However, an understanding of where the current flows in a

circuit is critical to implementing effective high speed circuit

design. The length of the current path is directly proportional to

the magnitude of parasitic inductances and therefore the high

frequency impedance of the path. High speed currents in an

inductive ground return will create an unwanted voltage noise.

VTHRESHOLD

VBIAS

TO REST OF AMP

VCC

–VEE

IT1

IT2

Figure 56. Simplified Input Stage

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