ADV7185KST Analog Devices Inc, ADV7185KST Datasheet - Page 13

• Manufacturer Part Number: ADV7185KST
• Description: IC VIDEO DECODER NTSC 80LQFP
• Manufacturer: Analog Devices Inc
• Type: Decoderr

Specifications of ADV7185KST

• Rohs Status: RoHS non-compliant
• Applications: DVD-RAM, Projectors, TV
• Mounting Type: Surface Mount
• Package / Case: 80-LQFP
• Adc/dac Resolution: 10b
• Screening Level: Commercial
• Package Type: LQFP
• Pin Count: 80
• Voltage - Supply, Analog: -
• Voltage - Supply, Digital: -
• Lead Free Status / RoHS Status: Not Compliant

CHROMINANCE PROCESSING
Figure 17 shows the chrominance data path. The 12-bit data
from the Y ADC (CVBS mode) or the C ADC (S-video) is first
demodulated. The demodulation is achieved by multiplying by
the locally generated quadrature subcarrier, where the sign of
the cos subcarrier is inverted from line to line according to the
PAL switch, and then low-pass filtering is applied to removed
components at twice the subcarrier frequency. For NTSC, the
phase of the locally generated subcarrier during color burst is
the same as the phase of the color burst. For PAL, the phase of
the color burst changes from line to line, relative to the phase
during active video, and the phase of the locally generated
subcarrier is the average of these two values.
The chrominance data is then passed through an antialiasing
filter, which is a band-pass filter to remove the unwanted lumi-
nance data. This antialiasing filter dramatically reduces the
external antialiasing filter requirements as it has only to filter
components above 25 MHz. In component mode, the demodu-
lation block is bypassed.
The next stage of processing is a shaping filter that can be used
to limit the chrominance bandwidth to between 0.5 MHz and
3 MHz; the CSFM[2:0] can be used to select these responses.
It should be noted that in CVBS mode, a filter of no greater
than 1.5 MHz should be selected as CVBS video is typically
band-limited to below 1.5 MHz. In S-video mode, a filter of up
to 2 MHz can be used. In component mode, a filter of up to
3 MHz can be used as component video has higher bandwidth
than CVBS or S-video.
The chrominance data is then passed through a resampler to
correct for line length variations in the input video. This
resampler is designed to always output 720 pixels per line for
standard PAL or NTSC. The resampler used on the ADV7185
is of very high quality as it uses 64 phases to resample the video,
giving 1/64 pixel resolution. The resampler is controlled by a
sync detection block that calculates line length variations on the
input video.
The final stage in the chrominance path, before it is applied to
an output formatter block, is chroma comb filter.
REV. 0
27MHz
CV/C
Figure 17. Chrominance Processing Path
COSINE
SINE
SUBCARRIER
RECOVERY
ALIASING
ALIASING
ANTI-
ANTI-
LPF
LPF
13.5MHz
13.5MHz
DETECTION
SYNC
SHAPING
LPF
RESAMPLE
U/V
CHROMA
FILTERS
6.75MHz
COMB
–13–
Figure 18. Chrominance Shaping Filter Responses
Figure 19. Chrominance Shaping Filter Responses
(Close-Up)
–0.2
–0.4
–0.6
–0.8
–1.0
–10
–20
–30
–40
–50
–60
1.0
0.8
0.6
0.4
0.2
0
0
0
0
SH1
0.5
0.5
SH2 SH3 SH4 SH5
1.0
1.0
FREQUENCY – MHz
FREQUENCY – MHz
1.5
1.5
SH1
2.0
2.0
SH2 SH3 SH4 SH5
2.5
2.5
SH6
ADV7185
3.0
3.0
3.5
3.5
SH6
4.0
4.0