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Simulators >> Circuit Simulators >> How to use bsource in spectre?
https://designers-guide.org/forum/YaBB.pl?num=1219634938

Message started by microant on Aug 24^th, 2008, 8:28pm

Title: How to use bsource in spectre?
Post by microant on Aug 24^th, 2008, 8:28pm

Hi all,
I want to use behavior model in cadence spectre, I found the help said that it can use bsource to achieve. well, I didn't find any instance in analogLib library can set the bsource attribute, would anyone can give me some suggestion?
thanks!

BR,
microant

Title: Re: How to use bsource in spectre?
Post by Ken Kundert on Aug 24^th, 2008, 10:42pm

Never use the bsource. Learn and use Verilog-A. It will serve you much better in the long run.

-Ken

Title: Re: How to use bsource in spectre?
Post by achim.graupner on Aug 25^th, 2008, 1:05am

Hi there,

1. Ken is right.
2. for the quick hack in schematic in analogLib you have {voltage; current} controlled {voltage; current} source: vcvs, ccvs, cccs, vccs. Do not try to model much more that a simple buffer - the schematic gets weired quickly soon.

Title: Re: How to use bsource in spectre?
Post by microant on Aug 25^th, 2008, 4:51am

thanks for above!
But how to realize the following function in spectre such as in hspice?
E1 a b vol=v(n1,n2)*k max=cc min=0
Verilog-A is so strong while if the expression quote many voltage or current it need many input/output port.

BR,
microant

Title: Re: How to use bsource in spectre?
Post by pancho_hideboo on Aug 25^th, 2008, 5:40am

microant wrote on Aug 24^th, 2008, 8:28pm:

I want to use behavior model in cadence spectre, I found the help said that it can use bsource to achieve. well, I didn't find any instance in analogLib library can set the bsource attribute

Many simulators except for Cadence Spectre had enhanced controlled sources which were familiar in HSPICE or PSPICE.
Also many model files provided from foundary are written in HSPICE netlist.
So "bsource" was introduced into Cadence Spectre for porting HSPICE model file which includes enhanced controlled sources.

So Cadence doesn't provide spectre view of bsource.
But you can use bsource in netlist.
See the result of "spectre -h bsource".

Actually any bsources are replaced to Verilog-A internally in Cadence Spectre.

microant wrote on Aug 25^th, 2008, 4:51am:

But how to realize the following function in spectre such as in hspice?
E1 a b vol=v(n1,n2)*k max=cc min=0
Verilog-A is so strong while if the expression quote many voltage or current it need many input/output port.

See http://www.designers-guide.org/Forum/YaBB.pl?num=1188726802/0

Title: Re: How to use bsource in spectre?
Post by microant on Aug 25^th, 2008, 7:19pm

Hi pancho_hideboo
thanks for your suggestion!
I find a alternative method to use bsource in spectre not by modifying the netlist.
copy instance 'vdc' from analogLib and modify the CDF parameter.
in simulation information, modify the item 'componetName' with bsource, in component parameters, add new param 'v', 'max_val' et, delete other params.
when use bsource, just like add voltage source and fill the expression in param 'v' and when generate netlist, it will be
v1 net1 net2 bsource v=express

BR,
Lin

Title: Re: How to use bsource in spectre?
Post by Ken Kundert on Aug 28^th, 2008, 7:33am

I recommend that you start with this ...

Code:

`include "disciplines.vams"
module clamp (pout, nout, pin, nin);
output pout, nout;
input pin, nin;
electrical pout, nout, pin, nin;
parameter real gain=1;
parameter real minimum=0;
parameter real maximum = 1 from (minimum:inf);
real in;

analog begin
in = V(pin, nin);
if (in > maximum) in = maximum;
if (in < minimum) in = minimum;
V(pout,nout) <+ gain*in;
end
endmodule

Title: Re: How to use bsource in spectre?
Post by Geoffrey_Coram on Aug 28^th, 2008, 1:32pm

Ken -
Shouldn't you do
out = gain * V(pin, nin);
if (out > maximum) out = maximum;
if (out < minimum) out = minimum;
V(pout,nout) <+ out;
?
Not that either one is good for convergence, but I don't quite know what your maximum was doing.

Title: Re: How to use bsource in spectre?
Post by Ken Kundert on Aug 29^th, 2008, 3:58am

Geoffrey,
Indeed, the model should be ...

Code:

`include "disciplines.vams"
module clamp (pout, nout, pin, nin);
output pout, nout;
input pin, nin;
electrical pout, nout, pin, nin;
parameter real gain=1;
parameter real minimum=0;
parameter real maximum = 1 from (minimum:inf);
real out;

analog begin
out = gain*V(pin, nin);
if (out > maximum) out = maximum;
if (out < minimum) out = minimum;
V(pout,nout) <+ out;
end
endmodule

Why do you think convergence will be a problem?
-Ken

Title: Re: How to use bsource in spectre?
Post by Geoffrey_Coram on Aug 29^th, 2008, 7:05am

Ken Kundert wrote on Aug 29^th, 2008, 3:58am:

Why do you think convergence will be a problem?

I was thinking that, when it's clamping, there is no derivative information, so the linear solver wouldn't "know" to change the input voltage to fix the output. I suppose, though, that it looks like an independent voltage source in that case, so it isn't a problem.

Title: Re: How to use bsource in spectre?
Post by imd1 on Sep 1^st, 2008, 1:11am

How about the discontinuous jump in the derivative when the hard limiter kicks in ?

i mean, the solver is doing its N-R iterations and using the derivative to "slide towards" the circuit solution at the node. If the solution is just below the hard limit breakpoint and the current estimate is above that level, there's no gradient information to point in which direction to go.

I assume that a smoothing function would be useful . Comments?

Title: Re: How to use bsource in spectre?
Post by Ken Kundert on Sep 1^st, 2008, 6:53pm

A common misconception.

Title: Re: How to use bsource in spectre?
Post by imd1 on Sep 2^nd, 2008, 1:17am

Ken Kundert wrote on Sep 1^st, 2008, 6:53pm:

A common misconception.

I see.