Datasheet

A =1X

INPUT

R = Z0

OPEN END

R = Z0

A =1X

INPUT

R = Z0

A =1X

INPUT

LMH6559

www.ti.com

SNOSA57C –APRIL 2003–REVISED MARCH 2013

APPLICATION NOTES

USING BUFFERS

A buffer is an electronic device delivering current gain but no voltage gain. It is used in cases where low

impedances need to be driven and more drive current is required. Buffers need a flat frequency response and

small propagation delay. Furthermore, the buffer needs to be stable under resistive, capacitive and inductive

loads. High frequency buffer applications require that the buffer be able to drive transmission lines and cables

directly.

IN WHAT SITUATION WILL WE USE A BUFFER?

In case of a signal source not having a low output impedance one can increase the output drive capability by

using a buffer. For example, an oscillator might stop working or have frequency shift which is unacceptably high

when loaded heavily. A buffer should be used in that situation. Also in the case of feeding a signal to an A/D

converter it is recommended that the signal source be isolated from the A/D converter. Using a buffer assures a

low output impedance, the delivery of a stable signal to the converter, and accommodation of the complex and

varying capacitive loads that the A/D converter presents to the OpAmp. Optimum value is often found by

experimentation for the particular application.

The use of buffers is strongly recommended for the handling of high frequency signals, for the distribution of

signals through transmission lines or on pcb's, or for the driving of external equipment. There are several driving

options:

• Use one buffer to drive one transmission line (see Figure 36)

• Use one buffer to drive to multiple points on one transmission line (see Figure 37)

• Use one buffer to drive several transmission lines each driving a different receiver. (see Figure 38)

Figure 36.

Figure 37.

Figure 38.

Product Folder Links: LMH6559