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

[gary <li...@la...>]

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.




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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