Datasheet

Video Luminance Matrix
V
IN
V
OUT
B
CE B
C
E
R
3
R
1
R
V
C
1
C
1
R
2
V
IN
V
OUT
x1
x1
150
Ω
OTA
3 B
2
E
C
8
V
BLUE
V
LUMINANCE
1820
Ω
(1)
V
GREEN
340
Ω
(1)
V
RED
665
Ω
(1)
200
Ω
200
Ω
+1
65
R
Q
= 250
Ω
(I
Q
= 11.2mA)
NOTE: (1) Resistors shown are 1% values
that produce 30%/59%/11% R/G/B mix.
H
(
s
)
+
a
0
s
2
) C
1
s ) C
0
+ *
R
1
R
V
1
1 ) sC
2
R
1
R
2
R
3
) s
2
C
1
C
2
R
1
R
2
State-Variable Filters
w
0
+
1
C
1
C
2
R
1
R
2
Ǹ
(10)
Q +
C
1
C
2
Ǹ
R
3
R
1
R
2
Ǹ
(11)
OPA860
www.ti.com ....................................................................................................................................................... SBOS331C – JUNE 2005 – REVISED AUGUST 2008
The inverting amplifier in Figure 59 amplifies the
three input voltages that correspond to the luminance
section of the RGB color signal. Different feedback
resistances weight the voltages differently, resulting
in an output voltage consisting of 30% of the red,
59% of the green, and 11% of the blue section of the
input voltage. The way in which the signal is weighted
corresponds to the transformation equation for
converting RGB pictures into B/W pictures. The
Figure 60. State Variable Filter Block Diagram
output signal is the black/white replay. It might drive a
monochrome control monitor or an analog printer
(hardcopy output).
Figure 61. State Variable Filter Using the OPA860
The transfer function is then:
Figure 59. Video Luminance Matrix
(9)
The ability of the OPA860 to easily drive a capacitor
can be put to good use in implementing state-variable
filters. A state-variable filter, or KHN filter, can be
represented with integrators and coefficients. For
example, the filter represented in the block diagram
of Figure 60 can easily be implemented with two
OPA860s, as shown in Figure 61 .
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