LT1399HV Linear Technology, LT1399HV Datasheet - Page 16

• Manufacturer Part Number: LT1399HV
• Description: Low Cost Dual and Triple 300MHz Current Feedback Amplifiers with Shutdown
• Manufacturer: Linear Technology

LT1398/LT1399/LT1399HV
TYPICAL
Single Supply RGB Video Amplifier
The LT1399 can be used with a single supply voltage of
6V or more to drive ground-referenced RGB video. In
Figure 10, two 1N4148 diodes D1 and D2 have been
placed in series with the output of the LT1399 amplifier
A1 but within the feedback loop formed by resistor R8.
These diodes effectively level-shift A1’s output down-
ward 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 324 . The gain resistor is created
from the parallel combination of R6 and R7, giving a
Thevenin equivalent 80.4
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
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16
PART NUMBER
LT1203/LT1205
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LT1675
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
[phone] FAX: [phone] www.linear-tech.com
A
PPLICATI
DESCRIPTION
150MHz Video Multiplexers
4-Input Video MUX with Current Feedback Amplifier
140MHz Current Feedback Amplifier
Low Cost Video Amplifiers
Dual/Triple Current Feedback Amplifier
Triple 2:1 Buffered Video Mulitplexer
V
IN
connected to 3.75V. This
O
Figure 10. Single Supply RGB Video Amplifier (1 of 3 Channels)
U
R1
1000
R2
1300
R3
160
R4
75
R5
2.32
5V
R6
107
R7
324
+
–
1/3 LT1399
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
reverse bias. 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
2:1 and Dual 2:1 MUXs with 25ns Switch Time
1100V/ s Slew Rate, Shutdown Mode
Single, Dual and Quad Current Feedback Amplifiers
130MHz Bandwidth, 0.1dB Flatness > 30MHz
Cascadable Enable 64:1 Multiplexing
2.5ns Switching Time, 250MHz Bandwidth
324
.
R8
1N4148
IN
D1
, the Thevenin equivalent signal arriving at
4.7 F
C1
1N4148
1398/99 F10
D2
75
R9
V
OUT
OUT
LINEAR TECHNOLOGY CORPORATION 1998
13989f LT/TP 0699 4K • PRINTED IN USA
equals a buffered version
IN
, with a source imped-
IN
with no additional