Re: gEDA-user: Phase and Magnitude of Current

[John Doty <jpd@xxxxxxxxx>]

On Apr 10, 2009, at 1:07 PM, Yamazaki R2 wrote:

> Sorry to randomly jump in here, but in ngspice, the only way to probe
> current is to probe a 0V voltage source? Theres no other work arounds
> for this?

It's classic SPICE technique.

> For example, if I had a very large hierachical design with
> 10,000 transistors in it and I wanted to plot the drain current of one
> particular transistor, I'd have to either edit the schematics and
> break apart the net and insert a 0V voltage source or hack the
> netlist?

Hardly difficult. The most important thing any professional needs to  
learn is not to get stuck on a trivial impediment.

> Isnt that a pretty important missing feautre? Gnucap lets you
> probe device currents without hacking the schematics.

Gnucap is a rapidly advancing work in progress. SPICE is  
conservative, stagnant, but still much more important. There's  
enormous knowledge and experience available for SPICE, little for  
gnucap. I expect gnucap will eventually surpass SPICE in all areas,  
but it isn't there yet.

>
> On Fri, Apr 10, 2009 at 11:33 AM, John Doty <jpd@xxxxxxxxx> wrote:
>>
>> On Apr 10, 2009, at 12:19 PM, awchang2@xxxxxxxxxxx wrote:
>>
>>> So spice won't actually calculate the current for me?
>>
>> In this particular case, you can also use Ohm's law to convert
>> voltage to current through the resistors, and KCL to get the reactive
>> currents versus time from your transient simulation. Of course, you
>> could also just do it entirely by hand from the complex impedances at
>> a given frequency. Spice is a little excessive here.
>>
>> Lots of ways to do this problem. You want to get good at this? Master
>> them all..
>>
>> John Doty              Noqsi Aerospace, Ltd.
>> http://www.noqsi.com/
>> jpd@xxxxxxxxx
>>
>>
>>
>>
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>
>
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John Doty              Noqsi Aerospace, Ltd.
http://www.noqsi.com/
jpd@xxxxxxxxx




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