HMP8170EVAL1 INTERSIL [Intersil Corporation], HMP8170EVAL1 Datasheet - Page 7

• Manufacturer Part Number: HMP8170EVAL1
• Description: NTSC/PAL Video Encoder
• Manufacturer: INTERSIL [Intersil Corporation]

appear to end early or start late since the HMP8170
controls the blanking edge rates.
The delay from the active edge of HSYNC to the 50% point of
the composite sync is 4-39 CLK2 cycles depending on the
HMP8170 operating mode. The delay is shortest when the
encoder is the timing master; it is longest when in slave mode.
CLK2 Input Timing
The CLK2 input clocks all of the HMP8170, including its
video timing counters. For proper operation, all of the
HMP8170 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 5.
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
The encoder begins the video processing with the pixel input
data. It converts the 4:2:2 YCbCr data to 4:4:4 data. The
conversion is done by 2x upsampling the Cb and Cr data.
The CbCr upsampling function uses linear interpolation. The
HMP8170 then upsamples the 4:4:4 data to generate 8:8:8
data. Again, the encoder uses linear interpolation for the
upsampling.
Horizontal Filtering
Unless disabled, the HMP8170 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
RECTANGULAR PIXELS (BT.601)
SQUARE PIXELS
VIDEO STANDARD
(B, D, G, H, I) PAL
(B, D, G, H, I) PAL
(M) NTSC
(M) NTSC
(NC) PAL
(NC) PAL
(M) PAL
(N) PAL
(M) PAL
(N) PAL
TOTAL
PIXELS PER LINE
7
858
864
858
864
864
780
944
780
944
944
ACTIVE
TABLE 5. TYPICAL VIDEO TIMING PARAMETERS
720
720
720
720
720
640
768
640
768
768
HBLANK REGISTER VALUES
842 (0x34a)
853 (0x355)
842 (0x34a)
853 (0x355)
853 (0x355)
923 (0x39b)
923 (0x39b)
923 (0x39b)
758 (0x2f6)
758 (0x2f6)
START
HMP8170
shown in Figure 7. At this point, the HMP8170 also scales
the Y data to generate the proper output levels for the
various video standards.
The HMP8170 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 8.
122 (0x7a)
133 (0x85)
122 (0x7a)
133 (0x85)
133 (0x85)
118 (0x76)
155 (0x9b)
118 (0x76)
155 (0x9b)
155 (0x9b)
END
259 (0x103)
310 (0x136)
259 (0x103)
309 (0x135)
310 (0x136)
259 (0x103)
310 (0x136)
259 (0x103)
309 (0x135)
310 (0x136)
VBLANK REGISTER VALUES
START
19 (0x13)
22 (0x16)
19 (0x13)
21 (0x15)
22 (0x16)
19 (0x13)
22 (0x16)
19 (0x13)
21 (0x15)
22 (0x16)
END
(MHz)
CLK2
24.54
24.54
27.0
27.0
27.0
27.0
27.0
29.5
29.5
29.5