Digital Scan Operation - Sanyo CE32WH3-F Service Manual

DIGITAL SCAN OPERATION

100Hz Digital Scan Converter circuit
100Hz converter circuit consists of the following ICs.
- SAA4977H
A/D, D/A, Timing generator
- SAA4991WP
100Hz converting processor
- SAA4955TJ x2
1.9Mbit field memory
-MC74HC4046AF
PLL(Phase Locked Loop)
The Y/U/V signals decoded in the HOP IC (IC101) are sent to the scan converter circuit. The
Y/U/V signals are sent to SAA4977H through the AC coupling capacitors and converted to 8bit
digital data with 16MHz sampling clock at the A/D converting stage in the IC respectively.
SAA4977H has built-in L.P.F. and the input stage for A/D conversion, so no external L.P.F. are
required. The digitalised U/V signals are compressed with 1 by 4 at SAA4977H and sent to the
field memory IC, SAA4955T as the 8bit Y-signal and 4bit C-signal data stream. Two fields picture
information are always maintained by two field memory IC, SAA4955TJ.
SAA4991WP creates a 100Hz converted field picture information to display next field from these 2
field picture information, and sends this to SAA4977H. There are two ways to create a new field
picture information, the one is creating the compensation data by detecting the motion image in
Digital scan circuit
Y
U
V
HD
VD
F7YLV
IC7207
FIELD
MEMORY-1
Y/U/V
SWCK
15 26
SWC
26
28
IC7201
A/D, D/A
79
30
TIMING
CONTROLLER
76
<SAA4977H>
22
74
71
20
72
70
LLD
IC7203
IC7208
PLL
IC7205
SRCK
SCAN
62
CONVERTER
<SAA4991WP>
IC7202,IC7204
VCO
-6-
IC7206
FIELD
MEMORY-2
26
SRCK
2Y_out
2U_out
2V_out
2HD_out
2VD_out
Fig.-7