LMH6718 datasheet(12/16 Pages) NSC

12 / 16 page

Application Section (Continued)

LOAD TERMINATION

The LMH6718 can source and sink nearly equal amounts of

current.

DRIVING CABLES AND CAPACITIVE LOADS

When driving cables, double termination is used to prevent

reflections. For capacitive load applications, a small series

resistor at the output of the LMH6718 will improve stability

and settling performance. The Suggested R

S vs. CL plot,

shown below in Figure 10, gives the recommended series

resistance value for optimum flatness at various capacitive

loads.

TRANSMISSION LINE MATCHING

One method for matching the characteristic impedance (Z

of a transmission line or cable is to place the appropriate

resistor at the input or output of the amplifier. Figure 11

shows typical inverting and non-inverting circuit configura-

tions for matching transmission lines.

Non-Inverting gain applications:

•

Connect pin 2 as indicated in the table in the Closed

Loop Gain Selection section.

•

Make R

1,R2,R6, and R7 equal to ZO.

•

Use R

3 to isolate the amplifier from reactive loading

caused by the transmission line, or by parasitics.

Inverting gain applications:

•

Connect R

3 directly to ground.

•

Make the resistors R

4,R6, and R7 equal to ZO.

•

Make R

5 \ Rg =ZO.

The input and output matching resistors attenuate the signal

by a factor of 2, therefore additional gain is needed. Use C6

to match the output transmission line over a greater fre-

quency range. C6 compensates for the increase of the am-

plifier’s output impedance with frequency.

20040145

FIGURE 7. Dual Supply, A

V = −1V/V Configuration

20040146

FIGURE 8. Dual Supply, A

V = +1V/V Configuration

20040147

FIGURE 9. Dual Supply, A

V = +2V/V Configuration

20040166

FIGURE 10. Suggested R

S vs. CL

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