From: Jim Thompson
Subject: Re: SPICE and amp stability
References: <3DDBC8B8.16BF2A6D@ieee.org> <3DDD150A.9BBBF272@ieee.org>
X-Newsreader: Forte Agent 1.91/32.564
Date: Thu, 21 Nov 2002 17:58:55 GMT
NNTP-Posting-Date: Thu, 21 Nov 2002 12:58:55 EST
Organization: Cox Communications
On Thu, 21 Nov 2002 17:16:57 GMT,
In Newsgroup: sci.electronics.design,
Entitled: "Re: SPICE and amp stability",
Wrote the following:
|Jim Thompson, analog wrote:
|>> 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?
|> You lost me there "analog", what are you driving at? Parameterizing
|> behavioral gains proportionate to power supplies??
|Almost. Have you ever modeled the low frequency behavior of switching
|power supplies using average duty cycle controlled sources to replace
|the semiconductor switches? One essentially use E and G sources to
|make a "dc transformer" with a dynamic turns ratio that depends on the
|node voltage representing duty cycle. These behavioral expressions
|contain product terms, but what really gives the simulator fits are
|higher order expressions with both numerator and denominator terms and
|with terms that include sums, differences, especially involving
|constants. There are lots of non-linear real world devices that don't
|have a suitable built-in model in Pspice the behavior of which can,
|nevertheless, be captured quite well via behavioral modeling. Tunnel
|diodes, vacuum tube, arc discharges, high level control system blocks
|all come to mind.
|However, there are many ways to express essential the same model within
|Pspice. The trick is to come up with one that doesn't give the
|simulator fits when either it is searching for an initial solution to
|the system matrix or when it is running a transient simulation. That
|is what my question was about. -- analog
One of the tricks I've used is to give OpAmps a sine-squared transfer
function, smoothing the derivatives.
| 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 |
For proper E-mail replies SWAP "-" and "_"
I love to cook with wine. Sometimes I even put it in the food.