8

LT1192

FREQUENCY (Hz)

24

LT1192 • TA07

100M

10M

1M

100k

A = +10

V

R

= 910

Ω

R = 47

Ω

20

16

12

8

4

0

FB

G

CABLE

2

+

–

5V

7

LT1192

–5V

4

3

6

R

75

Ω

75

Ω

G

Cable Driver Voltage Gain vs Frequency

Double Terminated Cable Driver

APPLICATIO S I FOR ATIO

LT1192 • TA05

SUPPLY BYPASS CAPACITORS = 0.1

µF

1V/DIV

1mV/DIV

0V

LT1192 • TA06

SUPPLY BYPASS CAPACITORS = 0.1

µF + 4.7µF TANTALUM

1V/DIV

1mV/DIV

0V

Settling Time Poor Bypass

Settling Time Good Bypass

amplified to 1mV/DIV the settling time to 1mV is 4.132

µs

for the 0.1

µFbypass;thetimedropsto140nswithmultiple

bypass capacitors.

Cable Terminations

The LT1192 operational amplifier has been optimized as a

low cost video cable driver. The

±50mAguaranteedoutput

100

single 5V supply.

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

receiving end (75

Ω to ground) to absorb unwanted

energy. The best performance can be obtained by double

termination (75

Ω in series with the output of the ampli-

fier, and 75

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

termination is preferred because reflected energy is

absorbed 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. For a cable

driver with a gain of 5 (op amp gain of 10) the – 3dB

bandwidth is 56MHz with only 0.25dB of peaking.

Using the Shutdown Feature

The LT1192 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

Ω in parallel with the feedback resis-

tors. The amplifiers must be used in a noninverting con-

figuration for MUX applications. In inverting configura-

tions the input signal is fed to the output through the

feedback components. When the output is loaded with as

little as 1k

Ω from the amplifier’s feedback resistors, the

amplifier shuts off in 400ns. This shutoff can be under the

control of HC CMOS operating between 0V and – 5V.

0V

0V