LT1398/LT1399/LT1399HV
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 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.
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
reverse bias. 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
feedbackresistorR8is324Ω.Thegainresistoriscreated
from the parallel combination of R6 and R7, giving a
Thevenin equivalent 80.4Ω 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
107Ω
6V TO 12V
1000Ω
D1
D2
R9
75Ω
+
V
OUT
1N4148 1N4148
A1
R2
1300Ω
1/3 LT1399
–
R3
160Ω
R8
324Ω
V
IN
1398/99 F10
R4
75Ω
R7
324Ω
R5
2.32Ω
Figure 10. Single Supply RGB Video Amplifier (1 of 3 Channels)
RELATED PARTS
PART NUMBER
LT1203/LT1205
LT1204
DESCRIPTION
COMMENTS
150MHz Video Multiplexers
2:1 and Dual 2:1 MUXs with 25ns Switch Time
Cascadable Enable 64:1 Multiplexing
4-Input Video MUX with Current Feedback Amplifier
140MHz Current Feedback Amplifier
Low Cost Video Amplifiers
LT1227
1100V/µs Slew Rate, Shutdown Mode
LT1252/LT1253/LT1254
LT1259/LT1260
LT1675
Single, Dual and Quad Current Feedback Amplifiers
130MHz Bandwidth, 0.1dB Flatness > 30MHz
2.5ns Switching Time, 250MHz Bandwidth
Dual/Triple Current Feedback Amplifier
Triple 2:1 Buffered Video Mulitplexer
13989f LT/TP 0699 4K • PRINTED IN USA
16 LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
●
●
LINEAR TECHNOLOGY CORPORATION 1998
(408)432-1900 FAX:(408)434-0507 www.linear-tech.com
Linear [ Linear ]
