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Design Languages >> Verilog-AMS >> look up table in verilog-A and spectre support
https://designers-guide.org/forum/YaBB.pl?num=1235734092

Message started by rajdeep on Feb 27^th, 2009, 3:28am

Title: look up table in verilog-A and spectre support
Post by rajdeep on Feb 27^th, 2009, 3:28am

Hi all,

I heard once that Verilog-AMS supports look-up tables. Can it be done in Verilog-A and does Cadence
Spectre support this?

If yes, can someone post me a small code section how a look-up table can be implemented in verilog-A?

Thanks much!
Rajdeep

Title: Re: look up table in verilog-A and spectre support
Post by Geoffrey_Coram on Feb 27^th, 2009, 6:41am

$table_model is part of the Verilog-AMS LRM, so it should be supported. Here's an example, copied from the LRM:

Code:

module example_tb(a, b);
electrical a, b;
inout a, b;
analog begin
I(a, b) <+ $table_model(V(a,b),"sample.dat");
end
endmodule

and a completely fabricated data file:

Code:

#sample.dat
0 0
1 1
2 4
3 9
4 16

Title: Re: look up table in verilog-A and spectre support
Post by Andrew Beckett on Feb 27^th, 2009, 6:57am

spectre has supported this for several years.

Regards,

Andrew.

Title: Re: look up table in verilog-A and spectre support
Post by rajdeep on Feb 27^th, 2009, 7:31am

Thanks a lot Geoffrey! It's working!

I could not find this table_model in the Verilog-A LRM, so thought to ask about it straight away in the forum, and as expected got a quick and effective reply. :)

Thanks,
rajdeep

Title: Re: look up table in verilog-A and spectre support
Post by Andrew Beckett on Feb 27^th, 2009, 8:16am

Rajdeep,

I assume you must be looking in the wrong LRM? If it's the VerilogA LRM that's shipped with the Cadence tools, then it's in IC5141's VerilogA Reference Manual, and all MMSIM versions.

Andrew.

Title: Re: look up table in verilog-A and spectre support
Post by rajdeep on Feb 27^th, 2009, 9:19am

Hi Andrew,

I downloaded it from web couple of years back and still use that one.
It could be that the one that comes with Cadence is a more complete one.

thanks for your hint. I will try start using that one from now on..... 8-)

Rajdeep

Title: Re: look up table in verilog-A and spectre support
Post by Andrew Beckett on Feb 28^th, 2009, 9:59am

The Verilog AMS LRM is also on this site - look at the Verilog-AMS link at the top of the page...

Regards,

Andrew.

Title: Re: look up table in verilog-A and spectre support
Post by Geoffrey_Coram on Mar 3^rd, 2009, 6:49am

Indeed, $table_model was not in the Verilog-A LRM, nor in Verilog-AMS LRMs until version 2.2. It was donated by Cadence, though, so it was likely in Spectre for a while before that. You ought to get the latest LRM; it's free!

Title: Re: look up table in verilog-A and spectre support
Post by Dracon on Mar 8^th, 2009, 5:44am

And what if you want to use $table_model that could change your signal with frequency?
I know, you may say that laplace_nd function can be used but is there possibility to create linear changing attenuation?

Title: Re: look up table in verilog-A and spectre support
Post by pancho_hideboo on Mar 8^th, 2009, 8:53am

Dracon wrote on Mar 8^th, 2009, 5:44am:

but is there possibility to create linear changing attenuation?

What do you mean by "linear changing attenuation" ? Attenuation depending on frequency is linear value or dB value ?
If it is linear, show me example of dependencies of attenuation.

Title: Re: look up table in verilog-A and spectre support
Post by Dracon on Mar 8^th, 2009, 2:55pm

Yes you are right it is not linear, and this is not what I meant to write. What I want to achieve is to have some kind of impact on attenuation, in modelling cable for example, and express that as 2D look-up table(frequency, attenuation).
As far as I know the $noise_table is very flexible on this aspect but only for noise.

Title: Re: look up table in verilog-A and spectre support
Post by pancho_hideboo on Mar 8^th, 2009, 3:11pm

Dracon wrote on Mar 8^th, 2009, 2:55pm:

What I want to achieve is to have some kind of impact on attenuation, in modelling cable for example, and express that as 2D look-up table(frequency, attenuation).

See http://www.designers-guide.org/Forum/YaBB.pl?num=1227194040