Fwd: Q'slew behavior with a discontinuous Q

---------- Forwarded message ----------
From: Joachim Haase <Joachim.Haase@eas.iis.fraunhofer.de>
Date: Tue, Sep 11, 2012 at 3:29 AM
Subject: AW: Q'slew behavior with a discontinuous Q
To: ZHICHAO DENG <zhichaodeng@gmail.com>
Cc: "Ernst Christen (christen.1858@comcast.net)" <christen.1858@comcast.net>


 Hi Zhichao,****

** **

I think the basic problem is how to determine Q’DOT in your example. To my
opnion, at the discontinuity the left-hand side value and the right-hand
side value are 0.0. Thus, it seems to me that in the case of your example
Q’DOT equals 0.0 for all times. Then I expect, that Q2 should follow Q as
shown in the attached PDF. It seems at a first glance that this behavior
does not meet the intuition. However, it seems to be in accordance with the
current LRM. There is a difference on applying ´SLEW on a quantity and a
signal at a discontinuity. L****

** **

The crucial problem seems to be to determine the right hand-side value
Q’DOT at the discontinuity if  Q’DOT is not part of the equations that
describe the simulation problem. I miss in the LRM how to determine Q’DOT
in this case if Q’SLEW is applied. ****

** **

Kind regards,****

Joachim  ****

** **

*Von:* owner-vhdl-ams@eda.org [mailto:owner-vhdl-ams@eda.org] *Im Auftrag
von *ZHICHAO DENG
*Gesendet:* Montag, 10. September 2012 19:19
*An:* vhdl-ams@eda.org
*Betreff:* Q'slew behavior with a discontinuous Q****

** **

Hi all,

I have come across with an issue related to the correct behavior of Q'slew
in VHDL-AMS standard.

For the following pseudo example,
quantity Q, Q2 real :=0.0;
if (xxx)
    Q == 1.0;
else
    Q == 2.0;

Q2 == Q'slew(100, -100);

Suppose, quantity Q has an immediate jump at t0 from 1.0 to 2.0;

xxx: some digital condition.****

Q, Q2 are quantities.****

** **

The attached doc contains my interpretation of the LRM behavior with
illustrated figure. I also explain what may be the should-be behavior in
this case and another option to deal with this if my interpretation of LRM
is accurate.****

** **

Please share your thoughts on this issue.****

** **

Regards,****

Zhichao****

** **


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