PAL/NTSC/SECAM video decoder with adaptive PAL/NTSC comb ...
PAL/NTSC/SECAM video decoder with adaptive PAL/NTSC comb ...
PAL/NTSC/SECAM video decoder with adaptive PAL/NTSC comb ...
You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
Philips Semiconductors<br />
<strong>PAL</strong>/<strong>NTSC</strong>/<strong>SECAM</strong> <strong>video</strong> <strong>decoder</strong> <strong>with</strong> <strong>adaptive</strong> <strong>PAL</strong>/<strong>NTSC</strong><br />
<strong>comb</strong> filter, VBI-data slicer and high performance scaler<br />
Preliminary specification<br />
SAA7114H<br />
8.1.2.1 Clamping<br />
The clamp control circuit controls the correct clamping of<br />
the analog input signals. The coupling capacitor is also<br />
used to store and filter the clamping voltage. An internal<br />
digital clamp comparator generates the information <strong>with</strong><br />
respect to clamp-up or clamp-down. The clamping levels<br />
for the two ADC channels are fixed for luminance (60) and<br />
chrominance (128). Clamping time in normal use is set<br />
<strong>with</strong> the HCL pulse at the back porch of the <strong>video</strong> signal.<br />
The AGC (automatic gain control for luminance) is used to<br />
amplify a CVBS or Y signal to the required signal<br />
amplitude, matched to the ADCs input voltage range.<br />
The AGC active time is the sync bottom of the <strong>video</strong> signal.<br />
Signal (white) peak control limits the gain at signal<br />
overshoots. The flow charts (see Figs 7 and 8) show more<br />
details of the AGC. The influence of supply voltage<br />
variation <strong>with</strong>in the specified range is automatically<br />
eliminated by clamp and automatic gain control.<br />
8.1.2.2 Gain control<br />
The gain control circuit receives (via the I 2 C-bus) the static<br />
gain levels for the two analog amplifiers or controls one of<br />
these amplifiers automatically via a built-in Automatic Gain<br />
Control (AGC) as part of the Analog Input Control (AICO).<br />
handbook, halfpage<br />
255<br />
60<br />
1<br />
TV line<br />
analog line blanking<br />
GAIN<br />
HSY<br />
CLAMP<br />
HCL<br />
MGL065<br />
handbook, halfpage analog input level<br />
controlled<br />
ADC input level<br />
+3 dB<br />
0 dB<br />
(1 V (p-p) 18/56 Ω)<br />
−6 dB<br />
maximum<br />
range 9 dB<br />
minimum<br />
MHB325<br />
0 dB<br />
Fig.4<br />
Analog line <strong>with</strong> clamp (HCL) and gain<br />
range (HSY).<br />
Fig.5 Automatic gain range.<br />
2000 Mar 15 14