9

http://www.national.com

Transmission Line Matching

One method for matching the characteristic impedance

appropriate resistor at the input or output of the amplifier.

Figure 7 shows typical inverting and non-inverting circuit

configurations for matching transmission lines.

Figure 7: Transmission Line Matching

Non-inverting gain applications:

s

s

s

loading caused by the transmission line,

or by parasitics.

Inverting gain applications:

s

s

s

The input and output matching resistors attenuate the

signal by a factor of 2, therefore additional gain is needed.

of the amplifier’s output impedance with frequency.

Power Dissipation

Follow these steps to determine the power consumption

of the CLC450:

1. Calculate the quiescent (no-load) power:

2. Calculate the RMS power at the output stage:

are the RMS voltage and current across the

external load.

3. Calculate the total RMS power:

The maximum power that the DIP, SOIC, and SOT

packages can dissipate at a given temperature is

illustrated in Figure 8.

The power derating curve for

any CLC450 package can be derived by utilizing the

following equation:

where

θ

for a given package (°C/W)

Figure 8: Power Derating Curves

Layout Considerations

A proper printed circuit layout is essential for achieving

high

frequency

performance.

National

provides

evaluation boards for the CLC450 (730013-DIP, 730027-

SOIC, 730068-SOT) and suggests their use as a guide

for high frequency layout and as an aid for device testing

and characterization.

General layout and supply bypassing play major roles in

high frequency performance. Follow the steps below as

a basis for high frequency layout:

s

Include 6.8

µF tantalum and 0.1µF ceramic

capacitors on both supplies.

s

Place the 6.8

µF capacitors within 0.75 inches

of the power pins.

s

Place the 0.1

µF capacitors less than 0.1 inches

from the power pins.

s

Remove the ground plane under and around the

part, especially near the input and output pins to

reduce parasitic capacitance.

s

Minimize all trace lengths to reduce series

inductances.

s

Use flush-mount printed circuit board pins for

prototyping, never use high profile DIP sockets.

Evaluation Board Information

Data

sheets

are

available

for

the

CLC730013/

CLC730027 and CLC730068 evaluation boards. The

evaluation board data sheets provide:

s

Evaluation board schematics

s

Evaluation board layouts

s

General information about the boards

The CLC730013/CLC730027 data sheet also contains

tables of recommended components to evaluate several

of National’s high speed amplifiers. This table for the

CLC450 is illustrated below.

Refer to the evaluation

board data sheet for schematics and further information.

Components Needed to Evaluate the

CLC450 on the Evaluation Board:

s

s

Operation section of the evaluation board data

sheet for details)

(175

JA

°−

)

θ

Ambient Temperature (

°C)

0

0.2

0.4

0.6

0.8

1.0

-40 -20

0

20

40

60

80 100 120

180

AJP

AJE

SOT

140 160

CLC450

+

-

+

-