LT6550/LT6551
14
65501fa
+
–
450Ω 450Ω
+
–
450Ω 450Ω
+
–
450Ω 450Ω
1
R
G
B
P
R
Y
P
B
2
3
45
9
10
8
7
1070Ω
549Ω
2940Ω
75Ω
75Ω
174Ω
LT6550
261Ω
75Ω
–3.3V
3.3V 3.3V
+
–
450Ω 450Ω
+
–
450Ω 450Ω
+
–
450Ω 450Ω
1
2
3
45
9
10
8
7
105Ω
75Ω
133Ω
LT6550
–3.3V
6550/51 TAO3
Y = 0.299R + 0.587G + 0.114B
P
B
= 0.565(B – Y)
P
R
= 0.713(R – Y)
f
3dB
≈ 44MHz
RGB to YP
B
P
R
Component-Video Conversion
TYPICAL APPLICATIO
U
Consumer products require generation of YP
B
P
R
lumi-
nance/chrominance component signals, often from RGB
source content. The YP
B
P
R
format has a luminance signal
and two weighted color difference signals at baseband.
Even with their fixed internal gain resistors, two LT6550s
connected as shown easily implement the required con-
version matrix equations. The Y channel is a weighted
average of the 2X amplified RGB signals and with the
feedback connection of the Y channel output in the second
LT6550 back to the gain-resistor common pin, an implicit
Y subtraction is performed for the chroma channels and
the desired unity gain is produced for the Y-channel. The
necessary scaling of the color-difference signals is per-
formed passively by their respective output termination
resistor networks. Since this circuit naturally produces
bipolar chroma signals (±0.35V at the cable load) regard-
less of RGB offset, the simplest implementation is to
power the circuit with ±3.3V split supplies. With an avail-
able output swing of about 5.6V for this supply configura-
tion, the circuit handles video with composite syncs and/
or various offsets without difficulty.
