I've read numerous articles on how grounding in mixed signal PCBs should be handled, and I've observed the following 3 camps.
1. Solid ground with split power plane or power traces.
2. Split digital/analog ground plane, with star-point at power supply.
3. Split digital/analog ground plane, with star-point near to the mixed signal chip.
I'm designing a mixed-signal 4-layer PCB involving a BGA IC with both analog (tv and audio signals) and digital pins partitioned across the IC itself, ie analog and digital pins are more or less partitioned on the chip. The design recommendations were to use a split ground. I've seen app notes which recommend either placing ADCs across the split ground, or entirely in the analog ground by virtue that they consume less current. But my chip is a mostly digital processor with significant current consumption (arnd 100mAs).
The following are my questions.
1. Which grounding scheme (from the above 3) should I use? If split, where should be the recommended star point?
2. Should I place my IC over the analog ground, digital ground, or over the split?(considering the fact it's a 0.1mm pitch BGA, and hence placing over a split ground would mean very narrow separations between the 2 grounds)
3. How should we handle digital control traces that will have to route across the split planes?
Any advice is appreciated with thanks.
1. Solid ground with split power plane or power traces.
2. Split digital/analog ground plane, with star-point at power supply.
3. Split digital/analog ground plane, with star-point near to the mixed signal chip.
I'm designing a mixed-signal 4-layer PCB involving a BGA IC with both analog (tv and audio signals) and digital pins partitioned across the IC itself, ie analog and digital pins are more or less partitioned on the chip. The design recommendations were to use a split ground. I've seen app notes which recommend either placing ADCs across the split ground, or entirely in the analog ground by virtue that they consume less current. But my chip is a mostly digital processor with significant current consumption (arnd 100mAs).
The following are my questions.
1. Which grounding scheme (from the above 3) should I use? If split, where should be the recommended star point?
2. Should I place my IC over the analog ground, digital ground, or over the split?(considering the fact it's a 0.1mm pitch BGA, and hence placing over a split ground would mean very narrow separations between the 2 grounds)
3. How should we handle digital control traces that will have to route across the split planes?
Any advice is appreciated with thanks.
