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Design Languages >> Verilog-AMS >> Variable pulse generator
https://designers-guide.org/forum/YaBB.pl?num=1269815816

Message started by Nader K on Mar 28^th, 2010, 3:36pm

Title: Variable pulse generator
Post by Nader K on Mar 28^th, 2010, 3:36pm

Hello, I am new to verilog-A can somone help me create a fixed length pulse generator which generates a pulse when its input falls from one to zero?

Title: Re: Variable pulse generator
Post by Geoffrey_Coram on Mar 29^th, 2010, 6:36am

You should at least try to give this a start. People are willing to help you fix an issue, but not so likely to write the whole model for you. Have you looked at the models available in the Verilog-AMS model library on this site? (Click the Verilog-AMS tab in the header bar.)

Title: Re: Variable pulse generator
Post by Nader K on Mar 31^st, 2010, 12:38am

I am using this but its only working on the first falling edge, how can i fix it in order for it to work on every falling edge? Thanks

module fixed_pulse_generator(in,out);

parameter real td = 0.5n; // width of pulse
parameter real tt = 0n; // output transition time (s)
output out;
input in;
voltage in, out;
real Vout;

analog begin
@(cross(V(in), -1))
Vout = 1.2;
V(out) <+ transition(-Vout, td, tt);
V(out) <+ transition(Vout, 2*td, tt);
end

endmodule

Title: Re: Variable pulse generator
Post by Geoffrey_Coram on Apr 5^th, 2010, 5:46am

What should happen if you get two falling edges in less than "td" ? Ie, the first pulse isn't over before the second starts?

Title: Re: Variable pulse generator
Post by Marq Kole on Apr 6^th, 2010, 3:43am

Your code doesn't change anything after the cross: Vout is constant (=1.2) after the first negative edge. You will need both a cross event and a timer event to make Vout change levels and have the transition operator react to that.

Code:

module fixed_pulse_generator(in, out);

parameter real td = 0.5n; // width of pulse
parameter real tt = 0n; // output transition time (s)

output out;
input in;
voltage in, out;

real Vout, tend;

analog begin
@(cross(V(in), -1)) begin
Vout = -1.2;
tend = $abstime + td;
end
@(timer(tend))
Vout = 1.2;
V(out) <+ transition(Vout, td, tt);
end

endmodule

Title: Re: Variable pulse generator
Post by Slavian on Dec 17^th, 2010, 12:20pm

When I'm trying to run it (using Cadence Virtuoso) I don't see any graph, only the following message is displayed:
"Unable to plot expression <VT("net5"...(itc.) because it does not evaluate to an object that can be plotted, like a waveform or parametric wave. See the Visualization & Analysis Tool documentation for information about the types of objects that can be plotted in Visualization & Analysis Tool. Only the expressions that evaluate to those objects can be plotted."

Does anyone know what does it mean and how to make it work?
Thanks.

Title: Re: Variable pulse generator
Post by Geoffrey_Coram on Dec 20^th, 2010, 5:22am

Slavian wrote on Dec 17^th, 2010, 12:20pm:

"Unable to plot expression <VT("net5"...(itc.) because

Are you sure you've got that copied correctly? Why is there VT rather than just V?

Title: Re: Variable pulse generator
Post by Slavian on Dec 20^th, 2010, 5:26am

Geoffrey_Coram wrote on Dec 20^th, 2010, 5:22am:

Slavian wrote on Dec 17^th, 2010, 12:20pm:

"Unable to plot expression <VT("net5"...(itc.) because

Are you sure you've got that copied correctly? Why is there VT rather than just V?

Vt - Voltage transition. I want to use this pulse as a function of a time. So if i take a simulation 1 usec length, I expect to see the results... But I don't get any wave form at all...

Title: Re: Variable pulse generator
Post by Andrew Beckett on Jan 3^rd, 2011, 12:28am

It appears you're a bit confused here - the VT() function is an ADE calculator function that allows you to access the transient voltage on a named signal - it's nothing to do with the VerilogA model described in this post.

Most likely the problem is because the signal is not in the result database because it didn't get saved. Which simulator were you using? Can you maybe post the actual netlist you were using?

Best Regards,

Andrew.

Title: Re: Variable pulse generator
Post by Slavian on Jan 3^rd, 2011, 11:51am

Hi all!
I've solved the problem by writing a new function by myself.
Thank you.

Title: Re: Variable pulse generator
Post by Andrew Beckett on Jan 3^rd, 2011, 12:27pm

OK, although I cannot see what the VT() had to do with the VerilogA module described in this thread - so I've no idea why you needed to rewrite any "function"...

The VT() function is an ADE calculator function, whereas the module is a VerilogA module. Chalk and Cheese - two completely different things.

Regards,

Andrew.