Re: [Ngspice-users] Newbie question on simulating a mosfet inverter

[Daniel C. H. <dan...@gm...>]

Gary,

Thanks for the advice but it was of no help. I've put the DC voltage
at Vgs because
ngspice was complaining that there was none.

And by the way... this is not my homework :) I'm studding this on my
own, following
the video lectures that MIT makes available at the OCW site.

On 12/21/06, gary <li...@la...> wrote:
> I'm assuming you are not in the course as the list owner might not like
> me doing your homework. The thing I spot that looks odd is the
> combination of "dc" in your vgs source. Assuming this parsed, I don't
> know how spice interprets that line. [which is why I did this as a post
> to the list rather than directly to you.] I suggest
> vgs in 0 pulse (0 5 0 100u 100u 1m 2m)
> or better yet
> vgs in 0 pulse (0 5 1m 100u 100u 1m 2m)
> I don't like to change the source at time zero, but prefer to see the
> settled circuit before I start the transient simulation.
>
> Your pull up should be 1k.

I've put a 5k pull up so that I would get I_D=1mA, which was the value
I found in
the datasheet, but I'm not so sure I got the V_GS_th thing right. I
have also tried
the 1k that appears on the schematics of the course notes, but with no
improvement.

>
>
>
>
> Daniel Cabrini Hauagge wrote:
> > Hello,
> >
> > I'm new to electronics and spice and I'm trying to simulate a simple
> > nmos inverter but my setup just doesn't seem to work. When I run the
> > simulation the output voltage stays at high level with some very small
> > spikes when the input changes (I guess this is due to the parasite
> > capacitors in the mosfet model). The only warning that ngspice gives
> > is that there is no level set for the mosfet, but seting the level to
> > 1, 2 or 3 didn't solve the problem.
> >
> > The input file I'm working on is this
> >
> > Title Trying to use MOSFET's in simulation
> >
> > .INCLUDE 2N7000.mod
> >
> > Vgs in 0 DC 5 PULSE 0 5 0 100u 100u 1m 2m
> > Vdd dd 0 DC 5V
> > R1  dd out 5k
> > * Zetex
> > Xmos out in 0 2N7000
> >
> > .CONTROL
> > run
> > tran 10u 10m 0 10u
> > plot v(out)
> > plot v(in)
> > .ENDC
> >
> > .END
> >
> > The MOSFET model I'm using can be found here
> > http://www.google.com/url?sa=t&ct=res&cd=1&url=http%3A%2F%2Fwww.zetex.com%2F3.0%2Fspice%2F2n7000.mod&ei=3gyKRYLtN4r2owLJ07SDDw&usg=__qD8BjNuCMI0VRztaP1SyJsusTb4=&sig2=D5dbHUWYoEe-1DeBVpauiA
> >
> > The datashet is here
> > http://www.google.com/url?sa=t&ct=res&cd=2&url=http%3A%2F%2Fwww.zetex.com%2F3.0%2Fpdf%2F2N7000.pdf&ei=3gyKRYLtN4r2owLJ07SDDw&usg=__9cXuGI67A1xQyzF-qIboRlcgMqA=&sig2=bZ1TCMt4tMEnXWYEk88FxA
> >
> > And the circuit I'm trying to model is this one
> > http://ocw.mit.edu/NR/rdonlyres/Electrical-Engineering-and-Computer-Science/6-002Circuits-and-ElectronicsFall2000/F0B2D731-3CBF-4762-851F-5299800C5300/0/demo07.pdf
> >
> > Any help would be greatly appreciated.
> >
> > Daniel Cabrini Hauagge
> >
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-- 
Daniel Cabrini Hauagge