CLC730231 Quad High Speed SOIC Op Amp Evaluation

Board

General Description

The CLC730231 evaluation board is designed to aid in the

characterization of National Semiconductor’s High Speed

quad SOIC operational amplifiers.

Use the evaluation board as a guide for high frequency

layout and as a tool to aid in device testing and character-

ization.

The evaluation board schematic is shown below in Figure 1.

Refer to the product data sheets for recommendations for

component values.

Basic Operation

By changing RIN and ROUT different input and output im-

pedances can be matched. The SMA connectors and board

traces are optimized for 50 to 75

Ω operation. Other imped-

ances can be matched but performance may be noticeably

different, especially high frequency response. Even with op-

timal layout board parasitics play a large part in high fre-

quency performance and different termination resistors will

change the frequency of the dominant parasitic poles/zeros.

Layout Considerations

Printed circuit board layout and supply bypassing play major

roles in determining high frequency performance. When de-

signing your own board use these evaluation boards as a

guide and follow these steps to optimize high frequency

performance:

1.

Use a ground plane

2.

Include large (~6.8 µF) capacitors on both supplies.

3.

Near the device use .01 µF ceramic capacitors from both

supplies to ground C1, C2.

4.

Remove the ground and power planes from under and

around the part, especially the input and output pins.

5.

Minimize all trace lengths

6.

Use terminated transmission lines for long traces.

Sample artwork for the CLC730231 Evaluation board is

included on the next page in Figure 2.

Inverting Operation

With slight modification this board can be modified for invert-

ing operation. Cut the input trace between the SMA connec-

tor and the RIN resistor leaving RIN connected to the non

inverting pin ( the non-inverting input needs a DC bias cur-

rent path). Solder a resistor between the input line and the

inverting input side of R

Leave R

as marked. For matching input impedance a parallel termi-

nating resistor can be added from the input line to the

unused ground pad from the empty R

sary trace cuts are shown in Figure 4.

Measurement Hints

The board is designed for 50

Ω input and output connections

into coaxial cables. For other impedances the terminating

resistors can be modified to help match different imped-

ances.

Do not use normal oscilloscope probes to test these circuits.

The capacitive loading will change circuit performance dras-

tically. Instead use low impedance resistive divider probes of

100 to 500

Ω. See Figure 3 for a sample resistive probe. The

Low impedance resistor should be 50- 450

Ω. The ground

connection should be as short as possible (~1/2”). Even with

careful use of these probes results should be considered

preliminary until verified with controlled impedance measure-

ments. Even the best probes will interfere with circuit opera-

tion to some degree. Also, tools, power cables, fingers etc.

near the device will change measurement results often

dramatically.

March 2004

© 2004 National Semiconductor Corporation

MS200972

www.national.com