TMC22191 CADEKA [Cadeka Microcircuits LLC.], TMC22191 Datasheet - Page 34

• Manufacturer Part Number: TMC22191
• Description: Digital Video Encoders/Layering Engine
• Manufacturer: CADEKA [Cadeka Microcircuits LLC.]

TMC22091/TMC22191
SCH Phase Error Correction
SCH refers to the timing relationship between the 50% point
of the leading edge of horizontal sync and the positive or
negative zero-crossing of the color burst subcarrier refer-
ence. SCH error is usually expressed in degrees of subcarrier
phase. In PAL, SCH is defined for line 1 of field 1, but since
there is no color burst on line 1, SCH is usually measured at
line 7 of field 1. The need to specify SCH relative to a partic-
ular line in PAL is due to the 25 Hz offset of PAL subcarrier
frequency. Since NTSC has no such 25 Hz offset, SCH
applies to all lines.
The SCH relationship is only important in the TMC22x91
when two video sources are being combined or if the com-
posite video output is externally combined with another
video source. In these cases, improper SCH phasing will
result in a noticeable horizontal jump of one image with
respect to another and/or a change in hue proportional to the
SCH error between the two sources.
SCH phasing can be adjusted by modifying BURPH and
SYSPH values by equal amounts. SCH is advanced/delayed
by one degree by increasing/decreasing the value of BURPH
and SYSPH by approximately B6
corrected with SYSPH and BURPH offsets of AAA
Video Test Signals
The TMC22x91 has two standard video test waveforms for
evaluating video signal integrity. They are selected and
controlled by the Format Control Register.
Setting the Format Control Register bits 0, 4, and 5 LOW
generates standard color bars at the COMPOSITE output
34
1
2
Figure 8. 100% Color Bars With 100% and 75% Chrominance Saturation
3
4
h
5
. An SCH error of 15 is
6
7
8
h
.
(Figure 11), the luminance component stair-step signal at the
LUMA output, and the chrominance component on the
CHROMA output. The six colors are 100% saturated PAL
and 75% saturated for NTSC.
The percentage color saturation is selectable via Misc.
Control Register 0E, bit 0.
The color bar test pattern comprises eight equal-width bars
during VA, the active video period. The Timing Register
value for CBL is found from:
If CBL is larger than this, the color bars are truncated at the
end of VA. If CBL is smaller than VA/8, the color bar
sequence will repeat, starting with another white bar. From
left to right color bars 1 to 8 should be white, yellow, cyan,
green, magenta, red, blue, and black.
The modulated ramp waveform is enabled by setting the For-
mat Control Register to 30
and constant-phase subcarrier modulation superimposed on a
linear ramp which slews from black to white during the
active video portion of each horizontal line (Figure 12). This
waveform is useful in making differential gain and differen-
tial phase measurements. Differential gain is a measure of
the variation in saturation of a color as the luminance com-
ponent is varied from black to white. Differential phase is a
measure of the variation in hue of a color as the luminance
component is varied from black to white.
CBL
=
VA
----------------- -
8
+
7
1
2
h
. It comprises constant-amplitude
3
4
PRODUCT SPECIFICATION
5
6
7
8
24387A