The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Modeling >> Behavioral Models >> Modeling DDS/DAC modulator
https://designers-guide.org/forum/YaBB.pl?num=1201457595

Message started by Faisal on Jan 27^th, 2008, 10:13am

Title: Modeling DDS/DAC modulator
Post by Faisal on Jan 27^th, 2008, 10:13am

Hi,

I am trying to model a DDS/DAC and quadrature modulator in Spectre-RF? Is it possible to model this in Spectre-RF?

My concern is that DDS/DAC requires transient simulations and modulator will require Spectre-RF?

Any ideas on how to do this ?

Title: Re: Modeling DDS/DAC modulator
Post by Stefan on Jan 27^th, 2008, 12:02pm

If you write good enough behavioral models, the modulator won't require spectreRF (however, some measurements might be faster with spectre RF).

Title: Re: Modeling DDS/DAC modulator
Post by Faisal on Jan 30^th, 2008, 1:25pm

Hi Stefan,

Thanks for the response. What do you think would be a better tool for system level exploration? Matlab, Spectre, ADS.. any suggestions?

Title: Re: Modeling DDS/DAC modulator
Post by Stefan on Jan 30^th, 2008, 3:26pm

That strongly depends on what you're trying to do.

If you want system simulations that can be simulated together with transistor level parts - use VerilogAMS.
For pure system level simulations with much IP reuse like modulated signals and so on - use Matlab.
I personally dislike ADS, but that's my own oppinion.

It all depends on how good you are writing models and how much control over your model's behaiour you desire...

Title: Re: Modeling DDS/DAC modulator
Post by Faisal on Feb 6^th, 2008, 6:52am

Hi Stefan,

Thanks once again !!

I would also prefer using SpectreRF, I can model my modulator quite easily. I have the following issues

1) How to model an accumulator in SpectreRF .. I need a go-around for the hidden state problem,
2) I am not clear if we can mix Verilog-AMS with SpectreRF?

Title: Re: Modeling DDS/DAC modulator
Post by Stefan on Feb 6^th, 2008, 6:56am

spectreRF is not a language, it's a simulator.
"Hidden state" is a phenomenom that occurs during periodic steady state analysis.
An accumulator behaves like a capacity ... that should be no problem to model.
However I thought we were talking about MIXED SIGNAL simulations.

And no, you can't use the Verilog-AMS language with the spectreRF simulator. (just verilogA with respect to hidden states)

Title: Re: Modeling DDS/DAC modulator
Post by Faisal on Feb 6^th, 2008, 7:19am

Yes you are right about SpectreRF that its a simulator : I use the language/Simulator interchangeably, this is misleading.... .
If I say count = count + 1 in VerilogA and run PSS analysis in SpectreRF, I sometimes get an error from the SpectreRF complaining about the hidden state. For some modules that I have from Cadence rflib, I see similar modeling.. but they dont run into problems

Title: Re: Modeling DDS/DAC modulator
Post by Faisal on Feb 6^th, 2008, 7:27am

module try(out_sin);

output out_sin;

electrical out_sin;

real count, period, cos_angle;

analog begin
@(initial_step("static") or initial_step("pss") ) begin
count = 0;
period = 1 / 10M ;
end
@(timer(period/10, period)) begin
count = count + 1;
end
V(out_sin) <+ cos(2*3.14*1M*count);
end
endmodule

Title: Re: Modeling DDS/DAC modulator
Post by Geoffrey_Coram on Feb 12^th, 2008, 6:41am

Faisal wrote on Feb 6^th, 2008, 7:19am:

If I say count = count + 1 in VerilogA and run PSS analysis in SpectreRF, I sometimes get an error from the SpectreRF complaining about the hidden state. For some modules that I have from Cadence rflib, I see similar modeling.. but they dont run into problems

I think Cadence provides some attribute ("instrumentation_module" ?) to disable the warning.

Title: Re: Modeling DDS/DAC modulator
Post by Frank Wiedmann on Feb 12^th, 2008, 7:09am

Geoffrey_Coram wrote on Feb 12^th, 2008, 6:41am:

I think Cadence provides some attribute ("instrumentation_module" ?) to disable the warning.

It's (* instrument_module *) in front of the module name, see http://sourcelink.cadence.com/docs/db/kdb/2005/July/11187476.html.

Title: Re: Modeling DDS/DAC modulator
Post by Faisal on Mar 3^rd, 2008, 1:40pm

Thank you Geoffrey and Frank for your replies. It was helpful in understanding