8

LT1195

receiving end (75

Ω to ground) to absorb unwanted en-

ergy. The best performance can be obtained by double

termination (75

Ω in series with the output of the amplifier,

and 75

Ω to ground at the other end of the cable). This

termination is preferred because reflected energy is ab-

sorbed at each end of the cable. When using the double

termination technique it is important to note that the signal

is attenuated by a factor of 2, or 6dB. This can be compen-

sated for by taking a gain of 2, or 6dB in the amplifier.

Using the Shutdown Feature

The LT1195 has a unique feature that allows the amplifier

to be shut down for conserving power, or for multiplexing

several amplifiers onto a common cable. The amplifier will

dissipates 15mW while maintaining a true high impedance

output state of 15k in parallel with the feedback resistors.

The amplifiers must be used in a noninverting configura-

tion for MUX applications. In inverting configurations the

input signal is fed to the output through the feedback

components. The following scope photos show that with

output slowly decays toward ground. Additionally, when

the output is loaded with as little as 1k the amplifier shuts

off in 700ns. This shutoff can be under the control of HC

CMOS operating between 0V and –5V.

S

APPLICATI

I FOR ATIO

Power Supply Bypassing

The LT1195 is quite tolerant of power supply bypassing.

In some applications a 0.1

µF ceramic disc capacitor

placed 0.5 inches from the ampifier is all that is required.

In applications requiring good settling time, it is important

to use multiple bypass capacitors. A 0.1

µF ceramic disc in

parallel with a 4.7

µF tantalum is recommended.

Cable Terminations

The LT1195 operational amplifier has been optimized as a

low cost video cable driver. The

±20mAguaranteedoutput

150

Ω, while operating on ±5V supplies.

–

+

LT1195

75

Ω

–5V

5V

CABLE

1195 AI01

3

2

7

4

6

75

Ω

FREQUENCY (Hz)

100k

1M

10M

100M

1195 AI02

8

6

4

2

0

–2

–4

–6

–8

–10

–12

Cable Driver Voltage Gain vs Frequency

Double-Terminated Cable Driver

Output Shutdown

1MHz SINE WAVE GATED OFF WITH SHUTDOWN PIN

When driving a cable it is important to terminate the cable

to avoid unwanted reflections. This can be done in one of

two ways: single termination or double termination. With

single termination, the cable must be terminated at the

1195 AI03