lt6559cud-trpbf Linear Technology Corporation, lt6559cud-trpbf Datasheet - Page 11

• Manufacturer Part Number: lt6559cud-trpbf
• Description: Low Cost 5v/?5v 300mhz Triple Video Amplifier In 3mm X 3mm Qfn
• Manufacturer: Linear Technology Corporation

TYPICAL APPLICATIONS
Buffered RGB to YP
An LT6559 and an LT1395 can be used to map RGB signals
into YP
The LT1395 performs a weighted inverting addition of all
three inputs. The LT1395 output includes an amplifi cation
of the R input by:
The amplifi cation of the G input is by:
Finally, the B input is amplifi ed by:
Therefore, the LT1395 output is:
–0.3R – 0.59G – 0.11B = –Y.
1 07
−
2 94
−
−
549
.
.
324
324
324
B
k
k
P
R
= −
= −
= −
“component” video as shown in Figure 7.
SOURCES
R
G
B
0 59
0 30
0 11
75Ω
.
.
.
B
P
ALL RESISTORS 1%
V
Y = 0.30R + 0.59G + 0.11B
P
P
R
R11
80.6Ω
R12
86.6Ω
R13
76.8Ω
S
B
R
= ±3V TO ±5V
Conversion
= 0.57 (B – Y)
= 0.71 (R – Y)
549Ω
1.07k
2.94k
–
+
LT1395
324Ω
Figure 7. RGB to YP
150Ω
1/3 LT6559
1/3 LT6559
+
1/3 LT6559
–
–
+
–
+
This output is further scaled and inverted by –301/150
= –2 by LT6559 section A2, thus producing 2Y. With the
division by two that occurs due to the termination resistors,
the desired Y signal is generated at the load.
The LT6559 section A1 provides a gain of 2 for the R sig-
nal, and performs a subtraction of 2Y from the section A2
output. The output resistor divider provides a scaling factor
of 0.71 and forms the 75Ω back-termination resistance.
Thus, the signal seen at the terminated load is the desired
0.71(R – Y) = P
The LT6559 section A3 provides a gain of 2 for the B
signal, and also performs a subtraction of 2Y from the
section A2 output. The output resistor divider provides a
scaling factor of 0.57 and forms the 75Ω back-termination
resistance. Thus the signal seen at the terminated load is
the desired 0.57(B – Y) = P
For this circuit to develop a normal sync on the Y signal,
a normal sync must be inserted on each of the R, G, and
B inputs. Alternatively, additional circuitry could be added
to inject sync directly at the Y output with controlled cur-
rent pulses.
B
P
A2
A3
A1
R
301Ω
Conversion
R
301Ω
301Ω
301Ω
301Ω
.
105Ω
133Ω
75Ω
B
261Ω
174Ω
.
6559 F07
P
Y
P
R
B
LT6559
11
6559f