LT1399 Linear Technology Corporation, LT1399 Datasheet - Page 12

• Manufacturer Part Number: LT1399
• Description: Low Cost Dual And Triple 300mhz Current Feedback Amplifiers With Shutdown
• Manufacturer: Linear Technology Corporation

LT1398/LT1399/LT1399HV
A
Buffered RGB to Color-Difference Matrix
Two LT1398s can be used to create buffered color-
difference signals from RGB inputs (Figure 8). In this
application, the R input arrives via 75 coax. It is routed
to the noninverting input of LT1398 amplifier A1 and to
a 1082 resistor R8. There is also an 80.6 termination
12
PPLICATI
V
OUT
V
IN
Figure 7. LT1399HV Output Voltage Swing
V
R
R
R
C
S
L
F
G
S
= 324
= 330pF
= 7.5V
= 16.9
= 162
O
U
S
SOURCES
R
G
B
75
50ns/DIV
I FOR ATIO
U
ALL RESISTORS 1%
V
R11
80.6
R12
86.6
R13
76.8
S
= 5V
W
Figure 8. Buffered RGB to Color-Difference Matrix
1082
2940
549
R10
R8
R9
1398/99 F07
U
1/2 LT1398
–
+
A2
324
R7
resistor R11, which yields a 75 input impedance at the
R input when considered in parallel with R8. R8 connects
to the inverting input of a second LT1398 amplifier (A2),
which also sums the weighted G and B inputs to create a
–0.5 • Y output. LT1398 amplifier B1 then takes the
–0.5 • Y output and amplifies it by a gain of –2, resulting
in the Y output. Amplifier A1 is configured in a noninvert-
ing gain of 2 with the bottom of the gain resistor R2 tied
to the Y output. The output of amplifier A1 thus results in
the color-difference output R-Y.
The B input is similar to the R input. It arrives via 75
coax, and is routed to the noninverting input of LT1398
amplifier B2, and to a 2940 resistor R10. There is also
a 76.8 termination resistor R13, which yields a 75
input impedance when considered in parallel with R10.
R10 also connects to the inverting input of amplifier A2,
adding the B contribution to the Y signal as discussed
above. Amplifier B2 is configured in a noninverting gain
of 2 configuration with the bottom of the gain resistor R4
tied to the Y output. The output of amplifier B2 thus
results in the color-difference output B-Y.
162
R6
1/2 LT1398
1/2 LT1398
+
1/2 LT1398
–
–
+
–
+
B2
B1
A1
324
R5
1398/99 F08
R1
324
R2
324
R4
324
R3
324
R-Y
Y
B-Y
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