hmp8156a Intersil Corporation, hmp8156a Datasheet - Page 13

• Manufacturer Part Number: hmp8156a
• Description: Ntsc/pal Video Encoder
• Manufacturer: Intersil Corporation

The delay from the active edge of HSYNC to the 50% point
of the composite sync is 4-39 CLK2 cycles depending on the
HMP8154/HMP8156A operating mode. The delay is shortest
when the encoder is the timing master; it is longest when in
slave mode.
Flicker Filter Blanking
When the flicker filter is enabled, BLANK occurs twice per line.
However, HSYNC does not change and still matches the
horizontal syncs of the composite output. The default timing of
BLANK with respect to HSYNC is shown in Figure 16.
HSYNC
BLANK
HSYNC
BLANK
Only the first unblanked period during each line time
determines when the active video will be output. Because of
the half line offset between the H and V syncs, pixel data
input begins (blanking ends) in the middle of the line time for
odd fields. However, it is still the unblanked period
immediately after HSYNC which generates the active region
of the output video. During even fields, the unblanking pulses
for the even numbered lines determine the output timing;
during odd fields, it’s the odd numbered lines.
When it is an output and the flicker filter is enabled, BLANK
generation is similar to that found in normal mode. The main
difference is that the encoder counts every CLK2 instead of
every other CLK2. The start and end times for each line’s
second unblanked interval are shifted slightly. The unblanked
intervals are the same number of pixels but the blanked
FIGURE 16. HSYNC AND BLANK TIMING WITH THE FLICKER
LINE #
LINE #
PIXEL
FIELD
PIXEL
FIELD
DATA
DATA
FIGURE 16A. BEGINNING AN EVEN FIELD
FIGURE 16B. BEGINNING AN ODD FIELD
FILTER ENABLED. VSYNC ALIGNS WITH EITHER
EDGE OF FIELD.
DETERMINES ACTIVE VIDEO IN OUTPUT.
0
0
†
13
†
UNBLANKED PERIOD WHICH
1
1
†
2
2
†
HMP8154, HMP8156A
3
3
†
intervals are not. The count values for BLANK transitions are
shown in Figure 17.
CLK2 Input Timing
The CLK2 input clocks all of the HMP8154/HMP8156A,
including its video timing counters. For proper operation, all
of the HMP8154/HMP8156A inputs must be synchronous
with CLK2. The frequency of CLK2 depends on the device’s
operating mode and the total number of pixels per line. The
standard clock frequencies are shown in Table 7.
Note that the color subcarrier is derived from the CLK2 input.
Any jitter on CLK2 will be transferred to the color subcarrier,
resulting in color changes. Just 400ps of jitter on CLK2 causes
up to a 1 degree color subcarrier phase shift. Thus, CLK2
should be derived from a stable clock source, such as a crystal.
The use of a PLL to generate CLK2 is not recommended.
Video Processing
Upsampling
Video processing begins with the 4:4:4 sampled YCbCr data
from the input processor. After overlay mixing and optional
2X upscaling or flicker filtering, the HMP8154/HMP8156A
upsamples the 4:4:4 data to generate 8:8:8 data. The
encoder uses linear interpolation for the upsampling.
Horizontal Filtering
Unless disabled, the HMP8154/HMP8156A lowpass filters
the Y data to 6.0MHz. Lowpass filtering Y removes any
aliasing artifacts due to the upsampling process, and
simplifies the analog output filters. The Y 6.0MHz lowpass
filter response is shown in Figure 18. At this point, the
HMP8154/HMP8156A also scales the Y data to generate the
proper output levels for the various video standards
The HMP8154/HMP8156A lowpass filters the Cb and Cr
data to 1.3MHz prior to modulation. The lowpass filtering
removes any aliasing artifacts due to the upsampling
process (simplifying the analog output filters) and also
properly bandwidth-limits Cb and Cr prior to modulation.
The chrominance filtering is not optional like luminance
filtering. The Cb and Cr 1.3MHz lowpass filter response is
shown in Figure 19.
HSYNC
BLANK
FIGURE 17. FLICKER FILTER BLANK OUTPUT TIMING
0
COUNTS. TOTAL DEPENDS ON FORMAT.
ACTIVE = START_H_BLANK -- END_H_BLANK
END_H_BLANK / 2
END_H_BLANK
START_H_BLANK
END_H_BLANK / 2 +
TOTAL -- ACTIVE
November 4, 2005
TOTAL
4343.4