LT1395/LT1396/LT1397
U
O
TYPICAL APPLICATI
Single Supply RGB Video Amplifier
input. Assuming a 75Ω source impedance for the signal
driving VIN, the Thevenin equivalent signal arriving at
A1’s positive input is 3V + 0.4VIN, with a source imped-
ance of 714Ω. The combination of these two inputs gives
anoutputatthecathodeofD2of2•VIN withnoadditional
DC offset. The 75Ω back termination resistor R9 halves
the signal again such that VOUT equals a buffered version
of VIN.
The LT1395 can be used with a single supply voltage of
6V or more to drive ground-referenced RGB video. In
Figure6,two1N4148diodesD1andD2havebeenplaced
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.
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
outputdropslowenoughthatthediodesmightotherwise
turn off. This means that this circuit works fine for
continuousvideoinput, butwillrequirethatC1chargeup
after a period of inactivity at the input.
Amplifier A1 is used in a positive gain configuration. The
feedbackresistorR8is255Ω.Thegainresistoriscreated
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
amplifier A1 to the cathode of D2. However, the video
input is also attenuated before arriving at A1’s positive
5V
C1
4.7µF
V
S
R1
R6
84.5Ω
6V TO 12V
1000Ω
D1
D2
R9
75Ω
+
–
V
OUT
1N4148 1N4148
A1
LT1395
R2
1300Ω
R3
160Ω
R8
255Ω
V
IN
1395/6/7 TA03
R4
75Ω
R7
255Ω
R5
2.32Ω
Figure 6. Single Supply RGB Video Amplifier (1 of 4 Channels)
RELATED PARTS
PART NUMBER
LT1227/LT1229/LT1230
LT1252/LT1253/LT1254
LT1363/LT1364/LT1365
LT1398/LT1399
LT1675
DESCRIPTION
COMMENTS
140MHz Single/Dual/Quad Current Feedback Amplifier 1100V/µs Slew Rate, Single Adds Shutdown Pin
Low Cost Video Amplifiers
Single, Dual and Quad 100MHz Current Feedback Amplifiers
1000V/µs Slew Rate, Voltage Feedback
70MHz Single/Dual/Quad Op Amps
Dual/Triple Current Feedback Amplifiers
Triple 2:1 Buffered Video Multiplexer
Low Cost Triple Current Feedback Amplifiers
300MHz Bandwidth, 0.1dB Flatness > 150MHz with Shutdown
2.5ns Switching Time, 250MHz Bandwidth
LT6559
300MHz Bandwidth, Specified at +5V and ±5V, 3mm × 3mm
QFN Package
139567fc
LT 0207 REV C • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
20
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© LINEAR TECHNOLOGY CORPORATION 1999
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
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