bt865a Conexant Systems, Inc., bt865a Datasheet - Page 60

• Manufacturer Part Number: bt865a
• Description: Ycrcb To Ntsc/pal Digital Video Encoder
• Manufacturer: Conexant Systems, Inc.

PC Board Considerations
3.5.3
Figure 3-3. Example of Mutual Inductance
3-6
Mutual Inductance Concerns
accuracy required by most industrial or consumer receivors. Note that a 30 ppm
tolerance constraint applies for Teletext and MPEG2.
Some applications call for maintaining correct Subcarrier-Horizontal (SC-H) phasing
for correct color framing, which requires subcarrier coherence within specified
tolerances over a 4-field interval for 525-line systems or 8 fields for 625-line systems.
Any CLK interruption (even during vertical blanking interval) which results in
nonstandard pixel counts per line can result in SC-H excursions outside the NTSC
limit of ±40 degrees (reference EIA RS170A) or the PAL limit of ±20 degrees
(reference EBU D23-1984).
Any deviation of the number CLK cycles between HSYNC* falling edges when in
SLAVE mode may result in automatic mode switching unless the internal control
registers VIDFORM, NONINTL and SQUARE are set for the desired mode of
operation.
The designer should prevent a situation where signals from other devices next to the
encoder cause the crystal to generate faulty clocks.
The Conexant encoder and any associated crystal that drives the CLK input should
physically be placed as far as possible from signal lines with excessive currents.
Excessive currents are defined to be greater than the Total Supply Current figure
listed in
In some systems, there are signal lines for controlling motors, LEDs, and thermal
heads. When a large current flows through these traces problematic noise can result
from the phenomenon of mutual inductance (See
Table
4-3.
Conexant
GND
CLK
Large Current
M
Figure
3-3).
100138_031
Bt864A/Bt865A Data Sheet
100138C
02/17/03