3

PC Board Layout

This amplifier’s frequency response depends greatly on the

care taken in designing the PC board (PCB). 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

(0.1

µF) chip capacitor works well in most cases.

Terminated microstrip signal lines are recommended at the

input and output of the device. Capacitance directly on the

output must be minimized, or isolated as discussed in the

next section.

An example of a good high frequency layout is the

Evaluation Board shown in Figure 3.

Driving Capacitive Loads

Capacitive loads, such as an A/D input, or an improperly

terminated transmission line will degrade the amplifier’s

phase margin resulting in frequency response peaking and

possible oscillations. In most cases, the oscillation can be

prior to the capacitance.

Figure 1 details starting points for the selection of this

combinations for the optimum bandwidth, stability, and

settling time, but experimental fine tuning is recommended.

Picking a point above or to the right of the curve yields an

overdamped response, while points below or left of the curve

indicate areas of underdamped performance.

system bandwidth well below the amplifier bandwidth of

the curves), the maximum bandwidth is obtained without

sacrificing stability. In spite of this, bandwidth decreases as

Evaluation Board

The performance of the HS-1412RH may be evaluated using

the HA5025 Evaluation Board, slightly modified as follows:

1. Remove the four feedback resistors, and leave the

connections open.

0

Ω resistors to GND.

The modified schematic for amplifier 1, and the board layout

are shown in Figures 2 and 3.

To order evaluation boards (part number HA5025EVAL),

please contact your local sales office.

0

100

200

300

400

0

10

20

30

40

50

LOAD CAPACITANCE (pF)

150

250

350

50

FIGURE 1. RECOMMENDED SERIES RESISTOR vs LOAD

CAPACITANCE

+5V

10

µF

0.1

µF

50

Ω

GND

GND

-5V

0.1

µF

10

µF

50

Ω

IN

OUT

or 0

1

2

3

4

5

6

7

14

13

12

11

10

9

8

FIGURE 2. MODIFIED EVALUATION BOARD SCHEMATIC

+

-

(NOTE)

FIGURE 3A. TOP LAYOUT

FIGURE 3B. BOTTOM LAYOUT

FIGURE 3. EVALUATION BOARD LAYOUT

HS-1412RH