hmp8190 Intersil Corporation, hmp8190 Datasheet - Page 8

• Manufacturer Part Number: hmp8190
• Description: Ntsc/pal Video Encoder
• Manufacturer: Intersil Corporation

The MSBs of the accumulated phase value (PHINT) are
used to address the encoder’s sine look up ROM. The sine
values from the ROM are pre-scaled to generate the proper
levels for the various video standards. Prescaling outside the
CbCr data path minimizes color processing artifacts. The
HMP8190/HMP8191 modulates the filtered 8:8:8
chrominance data with the synthesized subcarrier.
The SCH phase is 0 degrees after reset but then changes
monotonically over time due to residue in the NCO. In an
ideal system, zero SCH phase would be maintained forever.
In reality, this is impossible to achieve due to pixel clock
frequency tolerances and digital rounding errors. When the
PHINC source is BT.656 data, the SCH phase reset should
be disabled.
If enabled, the HMP8190/HMP8191 resets the NCO
periodically to avoid an accumulation of SCH phase error.
The reset occurs at the beginning of each field to burst
phase sequence. The sequence repeats every 4 fields for
NTSC or 8 fields for PAL.
-10
-20
-30
-40
-50
-60
-10
-20
-30
-40
-50
-60
0
0
0
0
NTSC OR PAL
RECTANGULAR PIXEL
CLK2 = 27.00MHz
PAL SQUARE PIXEL
CLK2 = 29.50MHz
NTSC SQUARE PIXEL
CLK2 = 24.54MHz
2
FIGURE 8A. FULL SPECTRUM
FIGURE 9A. FULL SPECTRUM
2
4
4
FREQUENCY (MHz)
NTSC OR PAL
RECTANGULAR PIXEL
CLK2 = 27.00MHz
NTSC SQUARE PIXEL
CLK2 = 24.54MHz
FREQUENCY (MHz)
6
8
6
8
FIGURE 9. Cb AND Cr LOWPASS FILTER RESPONSE
PAL SQUARE PIXEL
CLK2 = 29.50MHz
10
8
FIGURE 8. Y LOWPASS FILTER RESPONSE
12
10
HMP8190, HMP8191
14
12
Resetting the SCH phase every four fields (NTSC) or eight
fields (PAL) avoids the accumulation of SCH phase error at
the expense of requiring any NTSC/PAL decoder after the
encoder be able to handle very minor “jumps” (up to 2
degrees) in the SCH phase at the beginning of each four-
field or eight-field sequence. Most NTSC/PAL decoders are
able to handle this due to video editing requirements.
Composite Video Limiting
The HMP8190/HMP8191 adds the luminance and
modulated chrominance together with the sync, color burst,
and optional blanking pedestal to form the composite video
data. If enabled in the video processing register, the encoder
limits the active video so that it is always greater than one-
eighth of full scale. This corresponds to approximately one-
half the sync height. This allows the generation of “safe”
video in the event non-standard YCbCr values are input to
the device.
-0.5
-1.0
-1.5
-2.0
-2.5
-3.0
-0.5
-1.0
-1.5
-2.0
-2.5
-3.0
-3.5
-4.0
0
0
0
0
0.2
1
NTSC OR PAL
RECTANGULAR PIXEL
CLK2 = 27.00MHz
FIGURE 8B. PASS BAND
FIGURE 9B. PASS BAND
PAL SQUARE PIXEL
CLK2 = 29.50MHz
NTSC OR PAL
RECTANGULAR PIXEL
CLK2 = 27.00MHz
NTSC SQUARE PIXEL
CLK2 = 24.54MHz
0.4
NTSC SQUARE PIXEL
CLK2 = 24.54MHz
2
FREQUENCY (MHz)
FREQUENCY (MHz)
0.6
3
0.8
4
1.0
PAL SQUARE PIXEL
CLK2 = 29.50MHz
5
1.2
1.4
6
1.6
7