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Reply-To: "Kevin Aylward"
From: "Kevin Aylward"
Subject: Re: SPICE and amp stability
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
X-Inktomi-Trace: public1-pete2-5-cust19.pete.broadband.ntl.com 1037862859 17586 18.104.22.168 (21 Nov 2002 07:14:19 GMT)
Date: Thu, 21 Nov 2002 07:14:15 -0000
NNTP-Posting-Date: Thu, 21 Nov 2002 07:14:20 GMT
Mike Engelhardt wrote:
>>>>> Or is there some more correct way to determine the loop
>>>> You have to look at the *loop* gain. This is the open loop gain
>>>> around the *feedback* path. This involves setting up a circuit such
>>>> that the opamp has a closed loop for dc (or very, very low
>>>> frequencies), but open loop for the main plot. This is so the amp
>>>> will bias correctly. The easist way to see how this is done is to
>>>> run my SuperSpice
>>> This is a poor way of doing this. All you have to do insert a
>>> floating AC voltage source in series with the feedback at in front
>>> of a high impedance point of the circuit, typically the opamp
>>> input. Then do your .AC analysis, and plot the ratio of complex
>>> voltages to either side of the voltage source. This method also is
>>> a good one for bench use, called either a frequency response
>>> analysis or Venable.
>> It is a method that is used very often and does indeed work
>> in practise, despite not being exact. A poor method would be
>> something that basically don't work.
> Well, don't take it personally, but I thought it was a poor
> suggestion because it's more complicated
It what way is it more complicated? It would seem that having to
instruct the simulator to do a division rather then just drag test
points would be simplar.
>(not even accounting
> for having to download that piece of junk product of yours
> you were trying to promote with your followup)
I do feel sorry for you Mike. Have you considerd getting some help?
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
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