Yes, you're right, bypass to 1.5 V sees full fluctuation, to ground sees none, and for half the fluctuation you need to do both. But since this is termination, not a reference level, I don't think that matters that much anyway.
Another possibility is the termination currents are better handled by the supply than the ground. The termination currents would go back on dedicated power bus to the 1.5V supply and not cross talk to other devices via a shared ground. But this is just another small design subtlety.
Again, I don't think it's critical, especially if you have a good ground. The proof is that boards have gone both ways and work fine.
Yes, you're right, bypass to 1.5 V sees full fluctuation, to ground sees none, and for half the fluctuation you need to do both. But since this is termination, not a reference level, I don't think that matters that much anyway.
Another possibility is the termination currents are better handled by the supply than the ground. The termination currents would go back on dedicated power bus to the 1.5V supply and not cross talk to other devices via a shared ground. But this is just another small design subtlety.
Again, I don't think it's critical, especially if you have a good ground. The proof is that boards have gone both ways and work fine.
