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Design Languages >> Verilog-AMS >> Electrical Vs Real
https://designers-guide.org/forum/YaBB.pl?num=1225693458

Message started by gandhi_gaurav on Nov 2^nd, 2008, 10:24pm

Title: Electrical Vs Real
Post by gandhi_gaurav on Nov 2^nd, 2008, 10:24pm

I am designing a block with three inputs v1,v2,v3, one internal node v4 and the one output v5. Now v4 = 1 if (v1+v2+v3) > 3; V4 =0 if (v1+v2+v3) lies between 1 and 2 and V4 = -1 if (v1+v2+v3) <1.
V5 = sin(omega) * v4 where omega is externally specified.

Can anyone help me as how to model these mathematical functions in Verilog-AMS ?

Mainly I am stuck at which to define electrical and which net is real.

Thanks,
-Gaurav

Title: Re: Electrical Vs Real
Post by Geoffrey_Coram on Nov 3^rd, 2008, 5:36am

Are v1,v2,v3 digital inputs? You don't specify what v4 is if (v1+v2+v3) is, say, 2.5 (nor, actually, if it's exactly == 1 or == 3), yet clearly v5 is a real-valued output.

Title: Re: Electrical Vs Real
Post by jbdavid on Nov 3^rd, 2008, 2:28pm

If this is an osc, you'll need to integrate omega over time to get Phase (phi) and then take sin(phi) ..

this sounds like a variation on a voltage to frequency converter.. ?
--
my rule of thumb is this..
if the variable needs the spice-like integration (& numerical error) control handled well, make it electrical (or other continuous/conservative discipline).

g'luck!

Title: Re: Electrical Vs Real
Post by gandhi_gaurav on Nov 4^th, 2008, 11:20pm

Thanks for the reply.

Let me explain the problem again.

Just trying to realize spice statements like the following into veriloga

.FUNC Q(v1,v2,v3,v4) { (Cg1*v3+Cg2*v4+C1*v1+C2*v2)/E }
.FUNC VN(v) { CSUM*v/E }
.FUNC GAMMA(u) { IF(T==0,IF(u<0,-u,0),IF(u==0,T,u/(EXP(u/T)-1)))}

.FUNC ALPHA(v1,v2,v3,v4) { ROUND(-Q(v1,v2,v3,v4)+(CSUM/E)*(v1*RN2+v2*RN1)) }
In the above statements the function N_OPT calls Function Q, CSUM.

.FUNC R1L(n,v1,v2,v3,v4) {GAMMA(0.5 - n - Q(v1,v2,v3,v4) + VN(v1))/RN1} In the above statement the function R1L calls GAMMA.

Now my query is regarding
> best modeling practice regarding function calling functions the
> number of values that can be returned If declarations in functions are real and these cant take values which are defined electrical?
For example:-

`include "constants.vams"
`include "disciplines.vams"

module setmod2(v1, v2, v3, v4,v5);
inout v1, v2, v3, v4,v5;
electrical v1, v2 ,v3, v4,v5;
parameter real C1=1 ;
parameter real C2=1 ;
parameter real R1=1 ;
parameter real R2=1 ;
parameter real Cg1=1 ;
parameter real Cg2=0.1 ;
parameter real C0=0 ;
parameter real Q0=0 ;
parameter real TEMP=4.2 ;

parameter real PI=3.14 ;
parameter real E=1.5 ;
parameter real KB=1.3 ;
parameter real CSUM={C1+ C2+ Cg1+ Cg2+ C0} ;
parameter real T={TEMP*CSUM*5.3785467E14} ;
parameter real RN1={R1/(R1+ R2)} ;
parameter real RN2={R2/(R1+ R2)} ;

analog function real Q1;
input v_1, v_2, v_3, v_4;
real v_1,v_2, v_3,v_4;
Q1 = (Cg1*V(v_1)+Cg2*V(v_2)+C1*V(v_3)+C2*V(v_4))/(E+Q0) ; endfunction

analog begin

V(v5) <= Q1(v1,v2,v3,v4);

endmodule

Title: Re: Electrical Vs Real
Post by Geoffrey_Coram on Nov 5^th, 2008, 5:15am

A couple quick points:

gandhi_gaurav wrote on Nov 4^th, 2008, 11:20pm:

parameter real PI=3.14 ;

Ugh! If you're including constants.vams, why not use `M_PI?

Quote:

analog function real Q1;
input v_1, v_2, v_3, v_4;
real v_1,v_2, v_3,v_4;
Q1 = (Cg1*V(v_1)+Cg2*V(v_2)+C1*V(v_3)+C2*V(v_4))/(E+Q0) ; endfunction

analog begin

V(v5) <= Q1(v1,v2,v3,v4);

endmodule

Note that the LRM forbids you from using access function references in a function; you should change this to

Q1 = (Cg1*v_1+Cg2*v_2+C1*v_3+C2*v_4)/(E+Q0) ; endfunction

...

V(v5) <+ Q(V(v1), V(v2), V(v3), V(v4));

-Geoffrey

Title: Re: Electrical Vs Real
Post by Geoffrey_Coram on Nov 5^th, 2008, 5:17am

gandhi_gaurav wrote on Nov 4^th, 2008, 11:20pm:

In the above statements the function N_OPT calls Function Q, CSUM.

There's no N_OPT in what you posted ...

Quote:

In the above statement the function R1L calls GAMMA.

also no R1L ...