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Message started by microant on Sep 7^th, 2005, 1:13am

Title: how to
Post by microant on Sep 7^th, 2005, 1:13am

Hi All
i meet a problem with Hspice. i want to simulate a circuit with TRAN analysis and change the simulation temperature along with time.
is it possible to implement in Hspice or there is another way to achieve the same result? is anyone give me some suggestion. ???

thanks and best regards
microant

Title: Re: how to
Post by Paul on Sep 7^th, 2005, 12:59pm

Hello,

I'm not sure, but it seems to me temperature cannot be changed during a transient simulation. Maybe this is related to the fact that it is an input parameter to the device models.

Paul

Title: Re: how to
Post by Andrew Beckett on Sep 7^th, 2005, 4:08pm

I don't know whether this is possible in hspice. Currently it can't be done in spectre, but there was discussion about doing this for devices which already supported self-heating - that said, it's not been done yet AFAIK.

Regards,

Andrew.

Title: Re: how to
Post by microant on Sep 7^th, 2005, 5:22pm

Hi Andrew and Paul
Thanks for your response!
i didn't understand what you mean the following

that said, it's not been done yet AFAIK.
~~~~~~~~~~~~~~~~~~~~~~~~~

best regard
microant

Title: Re: how to
Post by Andrew Beckett on Sep 7^th, 2005, 10:14pm

AFAIK = "As Far As I Know"

Sorry for me using unfamiliar abbreviations. Lazy on my part.

Andrew.

Title: Re: how to
Post by Geoffrey_Coram on Sep 8^th, 2005, 8:39am

If the device supports self-heating, one could use a time-dependent voltage source to set the temperature from the simulation time. The device temperature in Kelvin is the same as the "voltage" of the thermal terminal. However, if you set the temperature in this manner, the device won't exhibit any *self*-heating; the voltage source is a perfect heat sink.

Title: Re: how to
Post by microant on Sep 8^th, 2005, 5:16pm

Hi Geoffrey_Coram
Thanks for your help! but i don't understand what means about 'the device supports self-heating', Could you explain in detail or illustrate? thanks.

best regards
microant

Title: Re: how to
Post by Geoffrey_Coram on Sep 9^th, 2005, 4:33am

The advanced bipolar transistors (mextram, hicum, vbic) support self-heating, by which the power dissipated in the device makes it warmer, which changes parameters such as the saturation current.

I think some high voltage MOS models in commercial simulators also support self-heating. And some implementations of BSIM3 have added it, as well.

But the point is, the model equations are already set up to change the parameters during the simulation, not just a dc temp or parameter sweep, but also a transient analysis.

Title: Re: how to
Post by Jaw on Oct 3^rd, 2005, 6:16pm

Is it really necessary to include the temperature change during transient simulation? For most of circuits, I guess the period of transient simulation is much shorter compared to the temperature varying period. It should be just enough to simulate a set of transient simulation in different corner temperatures.

Unless you need to simulate a circuit for a really long time ...

Title: Re: how to
Post by sheldon on Oct 3^rd, 2005, 6:37pm

Jaw,

Some circuits are sensitive to thermal effects, for example, the input
of a comparator. If one device is on and one device is off, then the
power and the temperature of the devices are different. When the
inputs return to the balanced state, there is now a time-dependent
offset voltage due to the difference in the device temperatures. This
can degrade the comparator's sensitivity.

The issue is rela

Title: Re: how to
Post by sheldon on Oct 3^rd, 2005, 6:42pm

Jaw,

Sorry about that Mozilla and I had a disagreement:-)

The problem is fairly common in real designs in particular
bipolar designs and many times circuits have specifications
for transient overdrive recovery.

Best Regards,

Sheldon