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Design Languages >> Verilog-AMS >> question on the "ddt" usage
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Message started by Patrick520 on Apr 3^rd, 2011, 8:12am

Title: question on the "ddt" usage
Post by Patrick520 on Apr 3^rd, 2011, 8:12am

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.

Title: Re: question on the "ddt" usage
Post by Sumit Adhikari on Apr 3^rd, 2011, 12:38pm

There are two questions :

1. How is the input signal in nature ?
2. What is that the output is driving ?

Regards,
Sumit

Title: Re: question on the "ddt" usage
Post by boe on Apr 4^th, 2011, 1:50am

Patrick520,

What do you want to do? Increase the blowup limit (for which simulator?) or change the value of the derivative?

B O E

Title: Re: question on the "ddt" usage
Post by Geoffrey_Coram on Apr 4^th, 2011, 12:04pm

Patrick520 wrote on Apr 3^rd, 2011, 8:12am:

Hi!
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?

Verilog-A provides the "slew" filter to do this, I believe.