Re: [Help-gnucap] Simulation of trifilar transformer

[a r]

On Sat, Aug 16, 2008 at 4:44 AM, al davis <address@hidden> wrote:
> On Tuesday 12 August 2008, a r wrote:
>> Last time I tried Gnucap I've been told that it does not
>> support mutual inductance. So, I guess, you will not be able
>> to model any kind of transformers in Gnucap.
>
> Yes it does, always has .. but only pairs.

Sorry, looks like I misunderstood your point before.

> So, try extending to 3 inductors ...
>
> .subckt trans3 (a1 a2 b1 b2 c1 c2)
> .param M12 = 'K12*sqrt(L1*L2)'
> .param M23 = 'K23*sqrt(L2*L3)'
> .param M13 = 'K13*sqrt(L1*L3)'
> l1 (a3 a2)       'L1'
> l2 (b3 b2)       'L2'
> l3 (c3 c2)        'L3'
> e21 (a4 a3 b3 b2) 'M12/L2'
> e31 (a1 a4 c3 c2) 'M13/L3'
> e12 (b4 b3 a3 a2) 'M12/L1'
> e32 (b2 b4 c3 c2) 'M23/L3'
> e13 (c4 c3 a3 a2) 'M13/L1'
> e23 (c2 c4 b3 b2) 'M23/L2'
> .ends
>
> Now call it:
>
> Xtrans (a1 a2 b1 b2 c1 c2) trans3 L1=.667 L2=.57 L3=.88
> + K12=.8 K23=.98 K13=.85
>
> ..... and there's your "trifilar transformer".

Thanks! This looks pretty good. BTW, do you think that this (lack of
support of more than 2 mutually coupled inductors) is something
specific to Gnucap or is it more general? I used to simulate similar
structures (namely, multiple bonding wire models) in both Hspice and
Spectre and they did not complain. Yet, I'd be better off making sure
they didn't quietly give bogus results.

-r.