ah_bhong wrote on Jan 25th, 2006, 6:07pm:Hi Murphy,
Thanks for the reply.
Yes, i agreed with you that there is a floating node at DC.
In fact, this is the place that i feel most uncomfortable with after checking through the DC operation of the circuit.
But i am uncertain by putting a nodeset at that point, does it guarantee that the circuit will work ?
Have you encountered similar problem before ?
cheers
bhong
Sorry if I led you astray with my earlier comment...it doesn't make sense to me now! It seemed similar to a problem I had with floating-gate MOSFETs. :-?
Disclaimer: I'm not sure this is relevant to the problem at hand, but it's true for the floating-gate stuff I've been looking at lately!
For a capacitively-coupled floating node, the simulator can't figure out what the right DC voltage is. Whatever you tell it is what it uses. So, I don't think it can find the 'right' value on its own...whatever you tell it is right. The way to make it work involves adding a resistor network that at DC gives the same node voltage that the cap-coupled charge distribution gives.
To answer your question more clearly, I don't think using a nodeset is going to give you a right answer unless you've already decided what the voltage at that node should be! The best it can do is get your simulation running because the DC solution can be found.