When target circuit include Hysteresis Buffer such as Schmitt Trigger Buffer,
it is very difficult to get convergence of periodical steady state analysis based on HB or Shooting-Newton approaches.

This issue is not concerned with specific vendor's simulator engine.

Is there anyone who have same experience ?
How do you overcome this issue ?

RFICDUDE wrote on Aug 26^th, 2010, 4:45pm:
I don't think so.

If we realize "Hysteresis" by Verilog-A, we will encounter "hidden state" problem.
But my circuits are real transistor level circuits, so there is no "hidden state" problem.

If we use "@cross()" to describe "Hysteresis" in Verilog-A, such module can't work in PSS analysis based on HB approach,
although it can work in PSS analysis based on Shooting-Newton approach.

RFICDUDE wrote on Aug 26^th, 2010, 4:45pm:
It is true for real transistor level circuits.

"Charges of Capacitor" are "State-Variables".

See http://www.designers-guide.org/Forum/YaBB.pl?num=1237890768/10#10

vp1953 wrote on Aug 27^th, 2010, 4:20pm:
I usually use 31 as Harmonics in HB.
I also tried 101 Harmonics in HB. But convegence can't be improved or succeeded.

Harmonics of 31 is generally enough for master large signal analysis, although it can not be enough for slave small signal analysis.

I think ill-convergence is due to a deadzone of Hysteresis Buffer.
There could be an oscillative behavior if an input signal is small around a deadzone.

pancho_hideboo wrote on Aug 25^th, 2010, 9:10am:
Again see start descriptions of this thread.

I tried following engines.
 - HB with Frequecy Domain Preconditioner in Agilent GoldenGate
 - HB with Time Domain Preconditioner in Agilent GoldenGate
 - TB(Time-Balance) in Agilent GoldenGate
 - TS(Time-Shooting) in Agilent GoldenGate
 - TB Assisted HB in Agilent GoldenGate
 - TS Assisted HB in Agilent GoldenGate
 - Transient Assisted HB with Frequecy Domain Preconditioner in Agilent GoldenGate
 - Transient Assisted HB with Time Domain Preconditioner in Agilent GoldenGate

 - PSS based on HB in Cadence Spectre
 - PSS based on Shooting-Newton in Cadence Spectre

Are you simulating just the trigger circuit by itself (i.e. are there other circuits also driven by the periodic source)?

Is the circuit behavioral or transistor level?
I only ask because I could play around with a behavioral circuit to see the circuit can be tricked into converging by adding a similar driven circuit without hysteresis included.
It is doubtful that my idea will work, but it is something to try.

I think (again I don't know for sure) that the hysteresis creates an ill condition for determining the periodicity of the solution because it perturbs the zero crossings when it makes a decision. You may have to think of ways (tricks) to make the output of the circuit periodic on average (I am not sure if this can easily be done).

There is nothing about hysteresis that in inherently problematic for PSS analysis. I suspect that there is something else that is causing the problem. If you simulate the circuit in Spectre, try using transient analysis with strobing and set the strobe period equal to the period of the expected fundamental tone. Then examine all the strobed signals and make sure they all appear to become constant valued. If they do not then your circuit does not have a periodic solution with that period. Check the supply currents first, they are most likely to show the problem.

-Ken

Again, there is nothing about hysteresis itself that is inherently problematic, as long as you generate a good starting point, which would be done naturally if you use an initial transient interval. That does not mean that there is something else about your hysteretic buffer that is causing the problem. I don't know what you mean by a dead zone, but I cannot see why a deadzone in general would be problematic. If the buffer were unstable, then that would be problematic because it would result in a non-periodic solution. That is why I recommended the strobing. With strobing you will be able to easily see if your circuit has a periodic solution for the period you chose.

-Ken