From: Mike Monett
X-Mailer: Mozilla 2.02 (Win16; I)
Subject: Re: Transistor amplifiers v. frequency in SPICE
References: <3E20D1C8.166C@sneakemail.com> <email@example.com>
Date: Sun, 12 Jan 2003 11:52:22 -0500
NNTP-Posting-Date: Sun, 12 Jan 2003 11:51:50 EST
Organization: Bell Sympatico
Paul Burridge wrote:
> Mike Monett wrote in message news:<3E20D1C8.166C@sneakemail.com>...
> > But first thing is to get SPICE to plot the AC response curves for you.
> > Lets see if we can help!
> Okay, Mike, here's the relevant bit from the deck file:
> .OPTIONS gmin = 1E-12 reltol = 1E-4 itl1 = 500 itl4 = 500
> + rshunt = 1G
> .AC Dec 200 20k 10Meg
> It seems to show a uniform flat Vout of zero volts from 200K to 10M,
> which of course is in contrast to the more sensible output
> levels the .TA generates. I would have expected an AC sweep to show
> Vout falling off with frequency, but it's just Zilcho the whole way through.
> Give it a try and see what you think. BTW, what is the "PH_DEG" plot
> that always seems to be generated supposed to us?
From your description, it seems the ac plot is showing the signal source,
not the output of the amplifier.
I'm not sure what the "PH_DEG" plot refers to. Normally, if you want the
phase response, you have to ask for it explicitly. Also, you forgot to
tell us what SPICE program you are running.
Just as a comment, you might like to increase the number of datapoints
from 200. It's not as critical as in .TRAN analysis, but I like to use as
many datapoints as possible before the simulation starts to get too slow.
In some cases, like crystal resonators or high-Q notch filters in a wide
bandwidth, you may have no choice but to use a large number of datapoints
and accept a slow simulation.