Fusion 878A
4.0 PC Board Layout Considerations
PCI Video Decoder
4.2 Split Planes and Voltage Regulators
100600B
Conexant
4-3
4.2 Split Planes and Voltage Regulators
The reference designs included in the
Bt878/Fusion 878A Hardware Users Guide
have no split planes. Careful attention has been given to creating one continuous
ground plane and one continuous power plane. This implementation produces
optimal video and audio performance. These boards have acceptable EMI
profiles. There is a voltage regulator on one design but it is for the TV tuner only.
An alternative implementation is obtained by adding split digital and analog
power and ground planes. Additional noise immunity can be obtained by adding a
voltage regulator for the analog and the digital power pins. Tests have been
performed with split planes and voltage regulators in a variety of combinations.
Measurements have been made and some increased noise reduction has been seen
on some systems. The noise improvements have not been substantial enough to
warrant additional cost. Additionally, splitting planes requires close consideration
to EMI and trace routing. If split planes or regulators are desired, some guidelines
are included.
•
Digital terminating resistors should be connected to digital supplies.
•
Components connected to analog pins should be connected to analog
ground.
The following pins have capacitors and/or resistors connected to them. The
other end of these components should be connected to analog ground.
•
Analog traces should be routed over analog planes only, when possible.
•
Digital traces should be routed over digital planes only, when possible.
•
Digital ground should be connected to chassis ground (bracket and
connector shields).
•
Digital and analog grounds should be connected near the voltage regulator.
AGCCAP
Pin 111
REFP
Pin 112
VCCAP
Pin 107
VRXP
Pin 103
VCOMI
Pin 104
VCOMO
Pin 105
RBIAS
Pin 106
SMXC
Pin 96