LT6550/LT6551
14
65501fa
+
–
450
450
+
–
450
450
+
–
450
450
1
R
G
B
PR
Y
PB
2
3
45
9
10
8
7
1070
549
2940
75
75
174
LT6550
261
75
–3.3V
3.3V
+
–
450
450
+
–
450
450
+
–
450
450
1
2
3
45
9
10
8
7
105
75
133
LT6550
–3.3V
6550/51 TAO3
Y = 0.299R + 0.587G + 0.114B
PB = 0.565(B – Y)
PR = 0.713(R – Y)
f3dB ≈ 44MHz
RGB to YPBPR Component-Video Conversion
TYPICAL APPLICATIO
U
Consumer products require generation of YPBPR lumi-
nance/chrominance component signals, often from RGB
source content. The YPBPR 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.