Re: MOS11 noise implementation in Verilog-A

Geoffrey,

    I agree that using extra nodes and a capacitor to implement the j
factor, will enable us to write most practical noise functions. The
Verilog-A compiler can even go further and try to reduce this node. But
wouldn't it be easier for the user to just write the complete noise PSD
equation directly, including the j factor. Of course, this would
require a language extension.

Ilya

Geoffrey.Coram wrote:

>Following an example in the Verilog-AMS LRM (4.5.3.5 on
>page 4-33), I believe the following code should produce
>the correlated gate noise of the MOS11 model (level 1101).
>
>I think Colin said that his simulator doesn't allow you
>to assign noise to a variable, and ADMS doesn't do noise
>at all, so I'm not quite sure anyone can test this out.
>But here goes.
>
>------------------
>
>// extra module items
>electrical noi; // extra internal node
>branch (noi) noiI, noiR, noiC;
>
>real n1, n2, n12;
>real rho_igth, nf1, nf2;
>
>// extra code for the analog block
>rho_igth = 0.4;
>nf1 = 27.0/40.0;
>nf2 = 1.0/(sqrt(nf1));
>
>n1 = white_noise(1.0 - rho_igth);
>n2 = white_noise(1.0 - rho_igth);
>n12 = white_noise(rho_igth);
>
>I(d,s) <+ NT_T / (Gmob*Gmob) * (Rideal - Tc_square * Ids * delpsi_s)
> * (n1 + n12);
>
>I(noiI) <+ NT_T * (3*Gm) * nf1 * (n2 + n12);
>I(noiR) <+ V(noiR) * (3*Gm) * nf2;
>I(noiC) <+ ddt(COX * V(noiC));
>
>I(g,s) <+ I(noiC);
>
>------------------
>
>The variables Gmob, Rideal, Tc_square, Ids, delpsi_s, and Gm
>are taken from the simkit_1.2.1 code for device_m1101i.c
>
>NT_T = temperature-adjusted value of parameter NT
>
>This does not account for drain/source swapping.
>
>What I've done is create an RC filter (R = 1/(3*Gm*nf2),
>C=Cox) driven by a white noise current source with PSD
>of NT_T * (3*Gm) * nf1. The power spectral density of
>the capacitor current is then
>
> NT_T * (3*Gm) * nf1 * || (2*pi*f*Cox)/(3*Gm*nf2 + j*2*pi*f*Cox) ||**2
>
> = NT_T * nf1 / (3*Gm*nf2*nf2) * pow(2*pi*f*Cox,2)
> -----------------------------------------------
> 1 + 1/(9*nf2*nf2)*pow(2*pi*f*Cox/Gm,2)
>
>
>With my particular choice of nf1 and nf2, this reduces to
>
> = NT_T * / (3*Gm) * pow(2*pi*f*Cox,2)
> -----------------------------------
> 1 + 0.075*pow(2*pi*f*Cox/Gm,2)
>
>The Philips documentation talks about 1/3 of the channel
>resistance in series with the oxide capacitance; in an
>ac noise analysis, you get a parallel combination of
>the noise current source, the R, and the C. I think
>this should give you nf1=nf2=1.0, but to match the
>equations implemented, you have to use the funny values
>given above.
>
>I think the fact that I'm sensing the capacitor current
>will give the factor of j (=sqrt(-1)) to match the value
>of rho_igth = 0.4j in the Philips report (eq. 2.120 in
>NLUR2002_802.pdf).
>
>
>-Geoffrey
>
>
Received on Wed May 19 18:59:32 2004