[SI-LIST] Re: Ring Oscillator

  • From: "Andrew Ingraham" <a.ingraham@xxxxxxxx>
  • To: <si-list@xxxxxxxxxxxxx>
  • Date: Sun, 11 May 2008 11:30:33 -0400

> The time period may differ from one cycle to the next in the
> output, so i have to measure the period for every consecutive cycle for
> about 1000 cycles.the only way i got to know is using 1000 .measure
> statements. however i wish to know if there is abetter way of doing this?

Read the waveforms into a SPICE plotting program and use its capabilities to
find the zero-crossings.  You usually get far better manipulation and
analysis capabilities in plotting and post-processing programs than with the
SPICE engine itself.  I don't use HSpice's own graphing programs so I don't
know what they are capable of.

However, it is questionable whether a SPICE run will show you all the
variations you will encounter, including noise, temperature changes, etc.
(unless you are clever enough to put these in to the run).  Some of the 5%
variation you talk about may be due to component tolerances, temperature,
and voltage, which a single SPICE transient run won't show you.

And in any event, many oscillators are not used during the first several
hundred (or million) cycles after they are started anyway, so the start-up
characteristics might not be interesting in reality.  If you were to measure
an actual oscillator with a scope or other instrument, you probably wouldn't
capture its waveform until a long time after it starts up.

Andy


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