Help, Corner Analysis doesn't work in vco, error in evaluating the expression.

I don't really understand what your problem is. You say the expression evaluates correctly - but then say "its corner analysis is not working". What does that mean?

Please give more details - perhaps with a few pictures - including info on the tools used and the versions used.

Andrew.

the nominal output is like this:

and i can simply get this output. it is under conditions of  ( temperature 27, typical typical pmos and nmos and 1.2 supply).

and when i tried to run it in a different conditions, such as running corner analysis, the tool gives:

*Error* ("error" 0 t nil ("*Error* drfGetWaveformYVec (DRL-18): argument not a valid srr waveform interface object nil"))


ERROR (ADE-1057): Could not evaluate expression
        Name:'kvco'
        Expression:'harmonic(xval(getData("/net15" ?result "pss_fd")) '1)'
     because of the following error(s)
        ("error" 0 t nil ("*Error* drfGetWaveformYVec (DRL-18): argument not a valid srr waveform interface object nil"))
     Ensure that the definition of the expression is correct.
*Error* deriv: can't handle deriv(nil)

im expecting output  like this. but this didn't show up to me, the error showed up instead.

i'm using virtuoso 6.1.7

the nominal output is like this:

and i can simply get this output. it is under conditions of  ( temperature 27, typical typical pmos and nmos and 1.2 supply).

and when i tried to run it in a different conditions, such as running corner analysis, the tool gives:

*Error* ("error" 0 t nil ("*Error* drfGetWaveformYVec (DRL-18): argument not a valid srr waveform interface object nil"))


ERROR (ADE-1057): Could not evaluate expression
        Name:'kvco'
        Expression:'harmonic(xval(getData("/net15" ?result "pss_fd")) '1)'
     because of the following error(s)
        ("error" 0 t nil ("*Error* drfGetWaveformYVec (DRL-18): argument not a valid srr waveform interface object nil"))
     Ensure that the definition of the expression is correct.
*Error* deriv: can't handle deriv(nil)

im expecting output  like this. but this didn't show up to me, the error showed up instead.

i'm using virtuoso 6.1.7

Your pictures are missing... so I don't fully understand what your setup looks like.

Andrew.

this is the first image,

the second, what i'm expecting:

Dear Abdallah,
Although you have not provided a lot of information (and hence my response may be incorrect), I've listed a few possibilities:
1. It appears (at least for the corner you are displaying the log for) the pss simulation likely did not complete correctly as the waveform can not be found. If you are simulating a ring VCO over corners, it is quite likely that its output frequency will vary significantly at each corner (with a fixed control voltage applied at each corner). if so, if you included the frequency in the pss analysis panel, the actual oscillator frequency at one or more corners may differ from the value you entered in the pss GUI. As a result, the pss analysis may fail for a corner where your manually entered frequency differs from the actual frequency.
2. A second possibility is that the value of tstab you entered is not sufficient for the oscillator to start and settle to its steady-state frequency at one or mroe corners.
3. A third possibility is that the VCO did not start at the corner for which you are displaying the log file. The start-up issue may (or may not) be a result of not setting a minimum integration time step for the analysis - it could also be a real design issue. To examine if the failure to start is a result of the simulator, you might try forcing the value of maxstep to a value of at least 1/20 or 1/100 of the expected VCO period.
I'm not sure if any of these potential issues may be the root cause - but thought I would pass them by. There are many other experts who monitor this forum and I am sure they will provide better solutions.
Shawn