question on verilogA term "ddt" usage

[Patrick520]

Hi!
I am new to verilogA.
I wanna describes an analog block which has a function of differentiating.
So, I describes a sentence as below:

"V(out)<+ ddt(V(in))"

But however, when using spectre to simulate it.
There is error like "V（t0,out）= 6.28 GV exceeds the blowup limit".

There is a case. When the input wave voltage changes very sharp, the differential result will be infinitely large.
So how to describe a bound for the differentiated value? How to set the limit?

Thanks in advance.

 

[pancho_hideboo]

Use slew() inside ddt().

 

[dick_freebird]

Perhaps the problem is that you are presenting unrealistic
inputs to the code-block. If you want it to return an
incorrect (but non-aborting) result then you will add
error checking and slow the thing down some I guess.
But it seems like it's trying to give you the right answer
for the insane condition you feed it.

 

[Patrick520]

Thanks. I will try it~