MC1377
I/Q System versus (R–Y)/(B–Y) System
The NTSC standard calls for unequal bandwidths for I and
Q (Figure 21). The MC1377 has no means of processing the
unequal bandwidths because the I and Q axes are not used
(Figure 22) and because the outputs of the (R–Y) and the
(B–Y) modulators are added before being output at Pin 13.
Therefore, any bandwidth reduction intended for the chroma
information must be performed on the composite chroma
information. This is generally not a problem, however, since
most monitors compromise the standard quite a bit.
Figure 23 shows the typical response of most monitors
and receivers. This figure shows that some crosstalk
between luma and chroma information is always present.
The acceptability of the situation is enhanced by the limited
ability of the CRT to display information above 2.5 MHz. If the
signal from the MC1377 is to be used primarily to drive
conventional non–comb filtered monitors or receivers, it
would be best to reduce the bandwidth at the MC1377 to that
of Figure 23 to lessen crosstalk.
Figure 20. NTSC Standard Spectral Content
Figure 21. Color Vector Relationship
(Showing Standard Colors)
(R–Y)
Red
(104°)
Purple
(61
(90
°
)
I
°)
Q
Luminance
I
Q (33°)
(123°)
Yellow
(168
°
)
(B–Y) 0
°
Color Burst
(180
0
1.0
2.0
3.0
4.0
°
)
Blue
(348°)
f, FREQUENCY (MHz)
Green
(241
Cyan
(284°)
°
)
Figure 22. Frequency Response of
Typical Monitor/TV
Chroma
Channel
Gain
Luminance
Channel
1.0
2.0
3.0 3.58 4.0
f, FREQUENCY (MHz)
13
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