LT1398/LT1399/LT1399HV
O U
W
U
PPLICATI
A
S
I FOR ATIO
resistor R11, which yields a 75Ω 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.
VIN
VOUT
1398/99 F07
VS = ±7.5V
RF = 324Ω
RG = 162Ω
50ns/DIV
The B input is similar to the R input. It arrives via 75Ω
coax, and is routed to the noninverting input of LT1398
amplifier B2, and to a 2940Ω resistor R10. There is also
a 76.8Ω termination resistor R13, which yields a 75Ω
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.
R
S = 16.9Ω
CL = 330pF
Figure 7. LT1399HV Output Voltage Swing
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 75Ω coax. It is routed
to the noninverting input of LT1398 amplifier A1 and to
a 1082Ω resistor R8. There is also an 80.6Ω termination
+
75Ω
R8
A1
SOURCES
R-Y
1082Ω
1/2 LT1398
R
–
R1
324Ω
R11
80.6Ω
R9
549Ω
R7
G
B
324Ω
R12
86.6Ω
R10
2940Ω
–
R6
162Ω
R5
R2
324Ω
324Ω
R13
76.8Ω
A2
1/2 LT1398
+
–
B1
Y
1/2 LT1398
+
R4
324Ω
R3
324Ω
–
ALL RESISTORS 1%
= ±5V
B2
B-Y
V
S
1/2 LT1398
1398/99 F08
+
Figure 8. Buffered RGB to Color-Difference Matrix
12
Linear [ Linear ]
