Re: gEDA-user: Frequency Response

[Daniel Nilsson <daniel@xxxxxxxxxxxxxxx>]

On Wed, May 18, 2005 at 12:29:27PM +0200, Davide Anastasia wrote:
> Il giorno lun, 16-05-2005 alle 21:08 -0400, Daniel Nilsson ha scritto:
> > On Tue, May 17, 2005 at 12:52:57AM +0200, Davide Anastasia wrote:
> > > Il giorno lun, 16-05-2005 alle 21:24 +0200, Leva ha scritto:
> > > > ..of what?
> > > 
> > > I've got only a schematic... It's possible to perform this task with
> > > Spice?
> 
> 
> Anyone can help me to find the error in this netlist? I'm a beginner of
> SPICE :(
> 
> Filter Net
> Vb 1 0 DC 4.5
> Vin in 0 DC 4.5 AC 4.5
> C1 in 2 22N
> C2 2 3 22N
> C3 3 out 22N
> R1 1 2 2200
> R2 1 3 2200
> 
> .ac dec 100 1 100meg
> .plot ac vdb(out) xlog
> .end


The error is that the node "out" is only connected via a capacitor to
node "3", this will cause spice to fail since there is no way to
perform a DC analysis and calculate the operating point on node
"out". If you really don't want a load on node "out", you must still
add a resistor to ground to support the DC analysis (which is always
done first even though this is an AC analysis).

Here's the corrected netlist (you were close!):

Filter Net
Vb 1 0 DC 4.5
Vin in 0 DC 4.5 AC 4.5
C1 in 2 22N
C2 2 3 22N
C3 3 out 22N
R1 1 2 2200
R2 1 3 2200
R3 out 0 10MEG

.ac dec 100 1 100meg
.plot ac vdb(out) xlog
.end

Daniel