Retard-o SPICE EXP Question

  • Thread starter Mike Rocket J. Squirrel E
  • Start date
M

Mike Rocket J. Squirrel E

Guest
Should be obvious to me, but my lack of skill interpreting SPICE
helpfiles is, after all, the stuff of legend. It's tough being a legend.

I want my voltage source to climb exponentially from 0 volts to 50 volts
after a 10ms delay and have a risetime constant of 1s.

But EXP 0 50 10ms 1

Creates a waveform that starts at 0 volts, then, after 10ms, plummets to
-50v, and climbs exponentially back up to 0.

How do you get it to sit at 0v for 10ms, then climb exponentially to +50v?

--
Mike "Rocket J Squirrel" Elliott
 
Mike Engelhardt wrote:

Mike,


How do you get it to sit at 0v for 10ms, then climb exponentially to +50v?


EXP(0 50 10ms 1 1e308)
Click to expand...
1e308? Some magic number?

--
Mike "Rocket J Squirrel" Elliott
 
Mike,

How do you get it to sit at 0v for 10ms, then climb
exponentially to +50v?

EXP(0 50 10ms 1 1e308)

1e308? Some magic number?
Click to expand...
It's just a time that is longer than I thought you'd have as the stop time
on your .tran statement.

--Mike
 
Mike Engelhardt wrote:
Mike,


How do you get it to sit at 0v for 10ms, then climb
exponentially to +50v?

EXP(0 50 10ms 1 1e308)

1e308? Some magic number?


It's just a time that is longer than I thought you'd have as the stop time
on your .tran statement.
Click to expand...
Yeah. A reasonable guess ... it's -- what? -- 3e300 years?


--
Mike "Rocket J Squirrel" Elliott
 
On Wed, 19 Nov 2003 06:37:49 GMT, "Mike Rocket J. Squirrel Elliott"
<j.michael.elliottAT@REMOVETHEOBVIOUSadelphiaDOT.net> wrote:

Mike Engelhardt wrote:
Mike,


How do you get it to sit at 0v for 10ms, then climb
exponentially to +50v?

EXP(0 50 10ms 1 1e308)

1e308? Some magic number?


It's just a time that is longer than I thought you'd have as the stop time
on your .tran statement.

Yeah. A reasonable guess ... it's -- what? -- 3e300 years?
Click to expand...
Mike obviously believes in giving plenty of leaway. :)

--

"I expect history will be kind to me, since I intend to write it."
- Winston Churchill
 
Paul Burridge wrote:

On Wed, 19 Nov 2003 06:37:49 GMT, "Mike Rocket J. Squirrel Elliott"
j.michael.elliottAT@REMOVETHEOBVIOUSadelphiaDOT.net> wrote:


Mike Engelhardt wrote:

Mike,



How do you get it to sit at 0v for 10ms, then climb
exponentially to +50v?

EXP(0 50 10ms 1 1e308)

1e308? Some magic number?


It's just a time that is longer than I thought you'd have as the stop time
on your .tran statement.

Yeah. A reasonable guess ... it's -- what? -- 3e300 years?


Mike obviously believes in giving plenty of leaway. :)
Click to expand...
For good reason! There's nothing more annoying than the premature
termination of a long transient simulation of those circuits you're
designing to last well beyond the projected age of the universe.

--
Mike "Rocket J Squirrel" Elliott
 
Mike,

How do you get it to sit at 0v for 10ms, then climb
exponentially to +50v?

EXP(0 50 10ms 1 1e308)

1e308? Some magic number?

It's just a time that is longer than I thought you'd have as the stop time
on your .tran statement.

Yeah. A reasonable guess ... it's -- what? -- 3e300 years?
Click to expand...
It's an easy-to-remember approximate upper limit of the
magnitude of a 64bit floating point number. Most any
reasonable number encountered in numerical computation would
be between -1.7e308 and 1.7e308. Numbers beyond that
range can be grouped with infinity. Yet, 1e308 is much longer than
the estimated age of the Universe. So 1e308 is slightly less than
infinity but much longer than forever.

--Mike

So many singularities, so little time.
 
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