LT1395 Linear Technology, LT1395 Datasheet - Page 12

• Manufacturer Part Number: LT1395
• Description: Single/Dual/Quad 400MHz Current Feedback Amplifier
• Manufacturer: Linear Technology

LT1395/LT1396/LT1397
TYPICAL
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 . The gain resistor is cre-
ated from the parallel combination of R6 and R7, giving
a Thevenin equivalent 63.5 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
RELATED PARTS
12
PART NUMBER
LT1227/LT1229/LT1230
LT1252/LT1253/LT1254
LT1398/LT1399
LT1675
LT1363/LT1364/LT1365
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
[phone] FAX: [phone] www.linear-tech.com
A
PPLICATI
DESCRIPTION
140MHz Single/Dual/Quad Current Feedback Amplifier
Low Cost Video Amplifiers
Dual/Triple Current Feedback Amplifiers
Triple 2:1 Buffered Video Mulitplexer
70MHz Single/Dual/Quad Op Amps
V
IN
O
Figure 3. Single Supply RGB Video Amplifier (1 of 4 Channels)
U
R1
1000
R2
1300
R3
160
R4
75
R5
2.32
5V
R6
84.5
R7
255
+
–
LT1395
6V TO 12V
A1
input. Assuming a 75 source impedance for the signal
driving V
A1’s positive input is 3V + 0.4V
ance of 714 . The combination of these two inputs gives
an output at the cathode of D2 of 2 • V
DC offset. The 75 back termination resistor R9 halves
the signal again such that V
of V
It is important to note that the 4.7 F 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.
V
S
IN
COMMENTS
300MHz Bandwidth, 0.1dB Flatness > 150MHz with Shutdown
1100V/ s Slew Rate, Single Adds Shutdown Pin
Single, Dual and Quad 100MHz Current Feedback Amplifiers
2.5ns Switching Time, 250MHz Bandwidth
1000V/ s Slew Rate, Voltage Feedback
255
.
R8
1N4148
IN
D1
, the Thevenin equivalent signal arriving at
4.7 F
C1
1N4148
1395/6/7 TA03
D2
75
R9
V
OUT
OUT
LINEAR TECHNOLOGY CORPORATION 1999
139567f LT/TP 0100 4K • PRINTED IN USA
equals a buffered version
IN
, with a source imped-
IN
with no additional