LT1395 Linear Technology, LT1395 Datasheet - Page 9

• Manufacturer Part Number: LT1395
• Description: Single/Dual/Quad 400MHz Current Feedback Amplifier
• Manufacturer: Linear Technology

A
termination when considered in parallel with R9. Using
superposition, it is straightforward to determine the
output of amplifier A2. Although inverted, it sums the R,
G and B signals in the standard proportions of 0.3R,
0.59G and 0.11B that are used to create the Y signal.
Amplifier A3 then inverts and amplifies the signal by 2,
resulting in the Y output.
SOURCES
R
G
B
Buffered Color-Difference to RGB Matrix
An LT1395 combined with an LT1396 can be used to
create buffered RGB outputs from color-difference sig-
nals (Figure 2). The R output is a back-terminated 75
signal created using resistor R5 and amplifier A1 config-
ured for a gain of +2 via 255 resistors R3 and R4. The
noninverting input of amplifier A1 is connected via 1k
resistors R1 and R2 to the Y and R-Y inputs respectively,
resulting in cancellation of the Y signal at the amplifier
input. The remaining R signal is then amplified by A1.
The B output is also a back-terminated 75
created using resistor R16 and amplifier A3 configured
for a gain of +2 via 255 resistors R14 and R15. The
noninverting input of amplifier A3 is connected via 1k
resistors R12 and R13 to the Y and B-Y inputs respec-
tively, resulting in cancellation of the Y signal at the
amplifier input. The remaining B signal is then amplified
by A3.
The G output is the most complicated of the three. It is a
weighted sum of the Y, R-Y and B-Y inputs. The Y input
75
PPLICATI
Figure 1. Buffered RGB to Color-Difference Matrix
ALL RESISTORS 1%
V
R11
82.5
R12
90.9
R13
76.8
S
= 5V
2320
845
432
R10
R8
R9
O
U
1/4 LT1397
–
+
S
A2
255
R7
I FOR ATIO
U
127
R6
W
1/4 LT1397
+
1/4 LT1397
–
–
1/4 LT1397
+
–
+
A3
A4
A1
255
R5
U
signal
1395/6/7 F01
R1
255
R2
255
R4
255
R3
255
R-Y
Y
B-Y
is attenuated via resistors R6 and R7 such that amplifier
A2’s noninverting input sees 0.83Y. Using superposition,
we can calculate the positive gain of A2 by assuming that
R8 and R9 are grounded. This results in a gain of 2.41 and
a contribution at the output of A2 of 2Y. The R-Y input is
amplified by A2 with the gain set by resistors R8 and R10,
giving an amplification of –1.02. This results in a contri-
bution at the output of A2 of 1.02Y – 1.02R. The B-Y input
is amplified by A2 with the gain set by resistors R9 and
R10, giving an amplification of – 0.37. This results in a
contribution at the output of A2 of 0.37Y – 0.37B.
If we now sum the three contributions at the output of A2,
we get:
It is important to remember though that Y is a weighted
sum of R, G and B such that:
If we substitute for Y at the output of A2 we then get:
The back-termination resistor R11 then halves the output
of A2 resulting in the G output.
A2
Y = 0.3R + 0.59G + 0.11B
A2
OUT
OUT
R-Y
B-Y
Figure 2. Buffered Color-Difference to RGB Matrix
Y
ALL RESISTORS 1%
V
S
= 3.40Y – 1.02R – 0.37B
= (1.02R – 1.02R) + 2G + (0.37B – 0.37B)
= 2G
= 5V
LT1395/LT1396/LT1397
205
261
698
R12
R13
R1
R2
R6
R8
R9
1k
1k
1k
1k
R7
1k
+
1/2 LT1396
–
+
–
+
1/2 LT1396
–
LT1395
A1
A3
A2
R3
267
R4
267
R10
267
R14
267
R15
267
75
75
75
R11
R16
R5
1395/6/7 F02
R
G
B
9