LT1395/LT1396/LT1397
20
139567fd
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507
●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 1999
LT 0709 REV D • PRINTED IN USA
RELATED PARTS
TYPICAL APPLICATION
PART NUMBER DESCRIPTION COMMENTS
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QFN Package
Single Supply RGB Video Amplifi er
The LT1395 can be used with a single supply voltage of
6V or more to drive ground-referenced RGB video. In
Figure 6, two 1N4148 diodes D1 and D2 have been placed
in series with the output of the LT1395 amplifi er 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.
Amplifi er A1 is used in a positive gain confi guration.
The feedback resistor R8 is 255Ω. The gain resistor
is created from the parallel combination of R6 and R7,
giving a Thevenin equivalent 63.5Ω connected to 3.75V.
This gives an AC gain of +5 from the noninverting input
of amplifi er A1 to the cathode of D2. However, the video
input is also attenuated before arriving at A1’s positive
input. Assuming a 75Ω source impedance for the signal
driving V
IN
, the Thevenin equivalent signal arriving at A1’s
positive input is 3V + 0.4V
IN
, with a source impedance
of 714Ω. The combination of these two inputs gives an
output at the cathode of D2 of 2 • V
IN
with no additional
DC offset. The 75Ω back termination resistor R9 halves
the signal again such that V
OUT
equals a buffered ver-
sion of V
IN
.
It is important to note that the 4.7μF 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 other-
wise turn off. This means that this circuit works fi ne for
continuous video input, but will require that C1 charge
up after a period of inactivity at the input.
–
+
A1
LT1395
D1
1N4148
C1
4.7μF
D2
1N4148
R9
75Ω
R8
255Ω
V
S
6V TO 12V
R7
255Ω
R5
2.32Ω
R4
75Ω
V
IN
R2
1300Ω
R1
1000Ω
5V
R6
84.5Ω
R3
160Ω
V
OUT
1395/6/7 TA03
Figure 6. Single Supply RGB Video Amplifi er (1 of 4 Channels)
