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Design Languages >> Verilog-AMS >> veriloga code of a switch
https://designers-guide.org/forum/YaBB.pl?num=1372166414

Message started by jovial on Jun 25^th, 2013, 6:20am

Title: veriloga code of a switch
Post by jovial on Jun 25^th, 2013, 6:20am

Hello everyone!!
I am modeling a simple voltage controlled switch which shld be a short ckt when control voltage is high, and open otherwise.
But the switch doesn't seem to work..
Can someone tell the mistake in my code given below...

-----------------------------------------------------------------------------------
`include "disciplines.vams"

module dig_ctrl_switch_va (p, n, ps, ns);
parameter real thresh=0.9; // threshold (V)
parameter real ron=10 from (1:inf); // on resistance (Ohms)
parameter real roff=100M from [1:inf); // off resistance (Ohms)
input ps, ns;
electrical p, n, ps, ns;

analog begin
@(cross( V(ps,ns) - thresh, 0 ))
$discontinuity(0);
if (V(ps,ns) > thresh)
I(p,n) <+ V(p,n)/ron;
else
I(p,n) <+ V(p,n)/roff;
end
endmodule

Title: Re: veriloga code of a switch
Post by Frank Wiedmann on Jun 25^th, 2013, 8:40am

You don't tell us what exactly is not working (error messages, simulation results, ...). However, it is obvious that your coding style can be improved. Take a look at chapter 3 "AMS Behavioral Modeling" of the Mixed-Signal Methodology Guide, which is available in four pdf files from http://www.eetimes.com/electronics-blogs/eda-designline-blog/4397605/Book-excerpt--Mixed-signal-methodology-guide-part-4. I would recommend you to use a transition function as shown on page 59 (the example is in Verilog-AMS, but a similar approach can be used in Verilog-A). By the way, Spectre has a similar component already built in, see http://www.cadence.com/community/forums/T/26543.aspx.

Title: Re: veriloga code of a switch
Post by boe on Jun 25^th, 2013, 8:41am

Jovial,
see LRM:
"You must declare the port direction for every port in the list of ports section of the module
declaration. To declare the direction of a port, use one of the following three syntaxes. ..."

Otherwise the code seems OK.

- B O E

Title: Re: veriloga code of a switch
Post by boe on Jun 25^th, 2013, 8:43am

Frank,
I fully agree. However, the V-AMS section of this site does offer a very similar example. So it should work.
- B O E

Title: Re: veriloga code of a switch
Post by Frank Wiedmann on Jun 25^th, 2013, 8:49am

It will probably work in simple circuits, but it might cause convergence problems in more complex ones.

Title: Re: veriloga code of a switch
Post by boe on Jun 25^th, 2013, 8:53am

Frank,
I also prefer the transition method...
- B O E