Termination

In high frequency applications reflections occur if signals

are not properly terminated To minimize reflection coaxial

cable with matching characteristic impedance to the signal

source should be used The other end of the cable should

be terminated with the same value terminator or resistor

For the commonly used cables RG59 has 75X characteris-

tics impedance and RG58 has 50X characteristics imped-

ance

Driving Capacitive Loads

Amplifiers driving capacitive loads can oscillate or have ring-

ing at the output To eliminate oscillation or reduce ringing

an isolation resistor can be placed as shown below in

Figure 4 The combination of the isolation resistor and the

load capacitor froms a pole to incease stability by adding

more phase margin to the overall system The desired per-

formance depends on the value of the isolation resistor the

bigger the isolation resistor the more damped the pulse

response becomes A 50X isolation resistor is recommend-

ed for initial evaluation

TLH12542 – 23

FIGURE 4 Driving Capacitive Load

Other High Speed and Video

Amplifiers

National Semiconductor has an extensive line of high speed

amplifiers with a range of operating voltage from 3V single

143mm - about the size of a grain of rice) and a wide SO-8

for better power dissipation

This op amp line includes -

LM6171

100 MHz low distortion amplifier with greater than

3000V ms slew rate

Voltage feedback design

supplies

LM7131

TinyPak (SOT23-5) video amplifier with 70 MHz

plies

LM7171

200 MHz voltage feedback amplifier with 100 mA

output current and 4000V ms slew rate Supply

supplies

Information on these parts is available from your National

Semiconductor representative

8-Pin Small Outline

Order Number LM6317IM or LM6317IMX

NSC Package Number M08A

http

www nationalcom

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