tulip
|
I designed a circuit having one feedback and one feed forward loop, the feed forward loop is used to provide a zero to improve the phase margin of the feedback loop. When I break the feedback loop, the stb analysis shows the loop is stable, but when I break the the feedforward loop, the stb analyais shows the loop is unstable. The transient reponse of the circuit is stable.
In cadence help file "spectreref.pdf", it says: The loop-based algorithm can only be performed on individual feedback loops to ensure that they are stable. Although the stability of all feedback loops is only a necessary condition for the whole circuit to be stable, the multi-loop circuit tends to be stable if all individual loops are associated with reasonable stability margins.
Does cadence mean that if one of the loop of a multi-loop circuit is unstable, the whole circuit is unstable? How can I check the stability of the circuit I designed?
Thank you very much.
|