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Design Languages >> Verilog-AMS >> How to Generate a Rectangular Pulse with Different Amplitudes
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Message started by Kevin Finn on May 30^th, 2013, 7:57am

Title: How to Generate a Rectangular Pulse with Different Amplitudes
Post by Kevin Finn on May 30^th, 2013, 7:57am

Hi everyone,

I've been trying to implement the following with Verilog A; however, I couldn't make it work thus far. What I wanna do is basically generate a rectangular pulse with more than 2 different amplitudes. For example, the amplitudes I want my pulse to have are 5, 3, 1, and -1 (in voltage).

During each unit interval, which's let's say 50 ns, I want my pulse to be equal to one of the abovewritten values.

I expect to code something like the following:

Code:

@(above($abstime - unit_interval) x = 5;
@(above($abstime - 2*unit_interval) x = 3;
@(above($abstime - 3*unit_interval) x = 1;
@(above($abstime - 4*unit_interval) x = -1;

pulse <+ transition (x);

However, the second line overwrites the first line, the third line overwrites the first two lines, and so on and so forth.

Could you please help me as to how I can code such a pulse in Verilog A?

Thanks in advance!

Title: Re: How to Generate a Rectangular Pulse with Different Amplitudes
Post by Ken Kundert on May 31^st, 2013, 1:16am

Try using @timer rather than @above. Use the second argument on the timer function to implement periodicity.

-Ken

Title: Re: How to Generate a Rectangular Pulse with Different Amplitudes
Post by Kevin Finn on May 31^st, 2013, 2:24am

Thanks for your response, Ken!

I actually had tried the @timer event before and couldn't make it work either.

Could you please tell me what's wrong with the following code? V(out) seems to be zero at all times when I simulate it.

Code:

@(timer(0, unit_interval)) x = 5;
@(timer(unit_interval, 2*unit_interval)) x = 3;
@(timer(2*unit_interval, 3*unit_interval)) x = 1;
@(timer(3*unit_interval, 4*unit_interval)) x = -1;

V(out) <+ transition(x, 0.0, period/100.0 );

Title: Re: How to Generate a Rectangular Pulse with Different Amplitudes
Post by Ken Kundert on May 31^st, 2013, 10:19am

You have not given enough of the model to see the problem. Please give the entire module.

-Ken

Title: Re: How to Generate a Rectangular Pulse with Different Amplitudes
Post by Kevin Finn on Jun 3^rd, 2013, 2:10am

Thanks for your response, Ken! Now, it's working, although I didn't get what the problem was before. I'm learning Verilog-A from scratch, so perhaps I did something nonesense.

Code:

module vsource_test (out);

output out;
voltage out;

parameter real unit_interval = 40n;

integer x;

analog begin

@(timer(0, unit_interval)) x = 5;
@(timer(unit_interval, 2*unit_interval)) x = 3;
@(timer(2*unit_interval, 3*unit_interval)) x = 1;
@(timer(3*unit_interval, 4*unit_interval)) x = -1;

V(out) <+ transition(x, 0, unit_interval/100);

end

endmodule