From: Jim Thompson
Subject: Re: SPICE and amp stability
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Date: Wed, 20 Nov 2002 22:37:16 GMT
NNTP-Posting-Date: Wed, 20 Nov 2002 17:37:16 EST
Organization: Cox Communications
On Wed, 20 Nov 2002 17:39:06 GMT,
In Newsgroup: sci.electronics.design,
Entitled: "Re: SPICE and amp stability",
Wrote the following:
|> If you're using PSpice, you can download, from my website, my
|> "Loopgain" part. This performs two passes, one with voltage drive,
|> and one with current drive, then computes gain and phase; all done
|> without perturbing the loop.
|This is general method that works regardless of the relative
|impedances at the insertion point within the loop to be measured,
|although most circuits have a convenient low impedance point (such
|as the error amp output) that enables accurate closed loop checking
|of loop gain with a single floating voltage source - both on the lab
|bench and on the circuit simulator.
|By the way, as long as one isn't using the student version and doesn't
|run out of nodes, making two copies in the same simulation file of the
|circuit being checked for loop gain allows running with both voltage
|and current drive simultaneously and may simplify probing the results.
I use a macro within Probe to take data from the two passes (the part
contains a .STEP statement), calculate and display the gain and phase.
|> This *may* be applicable to other "Spices" as well.
|I believe that this is a totally generic method, yes?
|You obviously are a Pspice aficionado, Jim. There is a rather clever
|way to force any circuit containing behavioral models, no matter how
|non-linear, to always successfully reach an initial operating point
|solution. It takes full advantage of Pspice's scheme of cutting back
|all power source as a convergence seeking ploy together with a unity
|voltage source as a reference node for taming the behavioral models.
|Can you guess what it is? -- analog
You lost me there "analog", what are you driving at? Parameterizing
behavioral gains proportionate to power supplies??
*** Note ***
I will be posting a new version of "Loopgain". The presently posted
version exhibits some conflicts with some other Probe functions, so
I've modified the Macro section.
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| Jim-T@analog_innovations.com Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
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