5

PC Board Layout

The frequency response of this amplifier depends greatly on

the amount of care taken in designing the PC board. The

use of low inductance components such as chip

resistors and chip capacitors is strongly recommended,

while a solid ground plane is a must!

Attention should be given to decoupling the power supplies.

A large value (10

μF) tantalum in parallel with a small value

chip (0.1

μF) capacitor works well in most cases.

Terminated microstrip signal lines are recommended at the

input and output of the device. Output capacitance, such as

that resulting from an improperly terminated transmission

line, will degrade the frequency response of the amplifier

and may cause oscillations. In most cases, the oscillation

can be avoided by placing a resistor in series with the

output.

Care must also be taken to minimize the capacitance to ground

seen by the amplifier’s inverting input. The larger this

capacitance, the worse the gain peaking, resulting in pulse

overshoot and eventual instability. To reduce this capacitance,

remove the ground plane under traces connected to -IN and

keep these traces as short as possible.

0

100

200

300

400

0

10

20

30

40

50

LOAD CAPACITANCE (pF)

150

250

350

50

FIGURE 1. RECOMMENDED SERIES OUTPUT RESISTOR vs

LOAD CAPACITANCE

FIGURE 2. SMALL SIGNAL PULSE RESPONSE

FIGURE 3. LARGE SIGNAL PULSE RESPONSE

200

150

100

50

0

-50

-100

-150

-200

TIME (5ns/DIV.)

2.0

1.5

1.0

0.5

0

-0.5

-1.0

-1.5

-2.0

TIME (5ns/DIV.)

HFA1155