12

LT1395/LT1396/LT1397

©LINEAR TECHNOLOGY CORPORATION 1999

139567f LT/TP 0100 4K • PRINTED IN USA

APPLICATI

TYPICAL

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

PART NUMBER

DESCRIPTION

COMMENTS

LT1227/LT1229/LT1230

140MHz Single/Dual/Quad Current Feedback Amplifier

1100V/

µs Slew Rate, Single Adds Shutdown Pin

LT1252/LT1253/LT1254

Low Cost Video Amplifiers

Single, Dual and Quad 100MHz Current Feedback Amplifiers

LT1398/LT1399

Dual/Triple Current Feedback Amplifiers

300MHz Bandwidth, 0.1dB Flatness > 150MHz with Shutdown

LT1675

Triple 2:1 Buffered Video Mulitplexer

2.5ns Switching Time, 250MHz Bandwidth

LT1363/LT1364/LT1365

70MHz Single/Dual/Quad Op Amps

1000V/

µs Slew Rate, Voltage Feedback

RELATED PARTS

Figure 3. Single Supply RGB Video Amplifier (1 of 4 Channels)

–

+

A1

LT1395

D1

1N4148

C1

4.7

µF

D2

1N4148

R9

75

Ω

R8

255

Ω

6V TO 12V

R7

255

Ω

R5

2.32

Ω

R4

75

Ω

R2

1300

Ω

R1

1000

Ω

5V

R6

84.5

Ω

R3

160

Ω

1395/6/7 TA03

Single Supply RGB Video Amplifier

The LT1395 can be used with a single supply voltage of

6V or more to drive ground-referenced RGB video. In

Figure 3, two 1N4148 diodes D1 and D2 have been placed

in series with the output of the LT1395 amplifier A1 but

within the feedback loop formed by resistor R8. These

diodes effectively level-shift A1’s output downward by 2

diodes, allowing the circuit output to swing to ground.

Amplifier A1 is used in a positive gain configuration. The

feedback resistor R8 is 255

Ω. The gain resistor is cre-

ated from the parallel combination of R6 and R7, giving

a Thevenin equivalent 63.5

Ω connected to 3.75V. This

gives an AC gain of + 5 from the noninverting input of

amplifier A1 to the cathode of D2. However, the video

input is also attenuated before arriving at A1’s positive

input. Assuming a 75

Ω source impedance for the signal

ance of 714

Ω. The combination of these two inputs gives

DC offset. The 75

Ω back termination resistor R9 halves

It is important to note that the 4.7

µF capacitor C1 has

been added to provide enough current to maintain the

voltage drop across diodes D1 and D2 when the circuit

output drops low enough that the diodes might otherwise

turn off. This means that this circuit works fine for

continuous video input, but will require that C1 charge up

after a period of inactivity at the input.