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The Designer's Guide Community Forum › Design Languages › Verilog-AMS › How to handle complex numbers and error function (erf(x))

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How to handle complex numbers and error function (erf(x)) (Read 9496 times)

Polux

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How to handle complex numbers and error function (erf(x))
Nov 04^th, 2011, 2:34am

As far as I know, verilogA does not support equation containing complex numbers and it doesnt work with the error function. I have just started a project simulating a specific FinFet for a company and I need to use equations based on the requiremets mentionated. Is there any way? or any clue that I could use in order to star my investigation.

Thanks.

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loose-electron Senior Fellow Offline Best Design Tool = Capable Designers Posts: 1638 San Diego California	Re: How to handle complex numbers and error function (erf(x)) Reply #1 - Nov 5^th, 2011, 1:44pm Its not Matlab. More designed for transient analaysis of currents and voltages. As a work around, consider processing two "signals" one to represent the real component, and the other to represent the imaginary part.
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Geoffrey_Coram Senior Fellow Offline Posts: 1999 Massachusetts, USA	Re: How to handle complex numbers and error function (erf(x)) Reply #2 - Nov 7^th, 2011, 11:18am I don't even see erf(x) supported in SystemVerilog (some extra features in SystemVerilog trickle down into V-AMS). I wonder if it's in VHDL-AMS (or one of its packages). I don't see an easy solution, sorry to say. Maybe you could create a table and use $table_model ?
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Polux Junior Member Offline Posts: 15	Re: How to handle complex numbers and error function (erf(x)) Reply #3 - Nov 11^th, 2011, 5:41am Oook.. thanks for the help.... I will continue researching, if I find solutions I will post it..
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Marq Kole

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Hmmm. That's
weird...

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Re: How to handle complex numbers and error function (erf(x))
Reply #4 - Nov 13^th, 2011, 1:22pm

An example implementation of the error function erf() can be found in the Numerical Recipes in C book. It's relatively easy to turn this C code into Verilog-A. Also C doesn't know a complex number data type and makes do with two real values representing real and imaginary parts as Geoffrey suggested.

Cheers,
Marq

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Polux

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Re: How to handle complex numbers and error function (erf(x))
Reply #5 - Nov 16^th, 2011, 1:38am

This is an example of the equations I have to run in VerilogA.. How would be your approach??.. I am still researching and try to find the most efficient solution..

u1v1 = cosh(pi * (xm + 1i*(toxs_t + Tch/2)) / (2 * toxs_t + Tch));

fz_0 = exp(g_0) * ((sqrt(pi) * Tch/2)/ (2 * sqrt(g_0))) * erf(sqrt(g_0))

thanks.

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Geoffrey_Coram Senior Fellow Offline Posts: 1999 Massachusetts, USA	Re: How to handle complex numbers and error function (erf(x)) Reply #6 - Nov 17^th, 2011, 6:05am For the erf call, I was suggesting something like this: real erf; erf = $table_model(sqrt(g_0), "erf.dat", "3E"); fz_0 = exp(g_0) * ((sqrt(pi) * Tch/2)/ (2 * sqrt(g_0))) * erf); where erf.dat is a text data file containing values generated by C or Matlab or something.
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Polux

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Re: How to handle complex numbers and error function (erf(x))
Reply #7 - Dec 6^th, 2011, 5:45am

Thank you very much for your help, implementing the erf(x) using table_models provides an easy way to obtain good results. Now, I was wondering if you have some extra information about how to implement complex numbers, as other researchers suggest is to separate the signal en their components and work indiviudality, etc. But how to start?

I would really appreciate the help.

thanks in advance.

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Geoffrey_Coram

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Re: How to handle complex numbers and error function (erf(x))
Reply #8 - Dec 14^th, 2011, 8:27am

Well, you have cosh(a + bi) in your example. So, you might start with some trigonometric identities:

cosh(x) = ( exp(x) + exp(-x) ) / 2
cosh(a+bi) = ( exp(a+bi) + exp(-a-bi) ) / 2
exp(iy) = cos(y) + i sin(y)
exp(a+bi) = exp(a) * exp(bi) = exp(a)*(cos(b) + i sin(b))

It gets a little messy; you might want to look at the whole set of equations and figure out if you really need all the parts.

If at first you do succeed, STOP, raise your standards, and stop wasting your time.

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Polux Junior Member Offline Posts: 15	Re: How to handle complex numbers and error function (erf(x)) Reply #9 - Dec 20^th, 2011, 5:27am Thanks again for your help. I follow your suggestion and others to change the expression of the equation that use complex numbers, and now I have been able to simulate the model in VerilogA, your help has been very usefull.
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Geoffrey_Coram Senior Fellow Offline Posts: 1999 Massachusetts, USA	Re: How to handle complex numbers and error function (erf(x)) Reply #10 - Dec 20^th, 2011, 5:49am I'm glad to hear it worked out for you.
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