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Design Languages >> Verilog-AMS >> NOISE FILTERING using VerilogAMS
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Message started by orciatichino on Jun 22^nd, 2012, 5:45am

Title: NOISE FILTERING using VerilogAMS
Post by orciatichino on Jun 22^nd, 2012, 5:45am

Hello!
I'm trying use VerilogAMS to filter a gaussian_distribution that represents a white noise source; to obtain a desired noise-shaping, I'm using a cascade of 5 stages of 1st order zero-pole filters.

I'm experiencing unconsistencies: the output amplitude, instead of being highly attenuated as required in a lowpass filtering, is several order of magnitudes greater than the input source.

Do anyone has suggestions or can identify mistakes?

I enclose an extract from my code.

parameter real fp1 = 7;
parameter real fp2 = 1e3;
parameter real fp3 = 4e3;
parameter real fz3 = 60e3;
parameter real NFB_db = -160;

real sp1, sp2, sp3, sz3, K;
real unif_jitt, filtered_jitt1, filtered_jitt2, filtered_jitt3, filtered_jitt4, filtered_jitt_out, filtered_jitt_5;

integer seed;

analog begin
@(initial_step) begin //Initial step declarations
sp1 = 2*`M_PI*fp1;
sp2 = 2*`M_PI*fp2;
sp3 = 2*`M_PI*fp3;
sz3 = 2*`M_PI*fz3;
K = sz3/sp3*100*100*pow(10, NFB_db/20);

seed = -561;
end

unif_jitt = $rdist_normal(seed, 0, 1);

filtered_jitt1 = laplace_nd(unif_jitt, {1, 1/(10*sp1)}, {1, 1/(sp1)});
filtered_jitt2 = laplace_nd(filtered_jitt1, {1, 1/(10*sp1)}, {1, 1/(sp1)});
filtered_jitt3 = laplace_nd(filtered_jitt2, {1, 1/(10*sp2)}, {1, 1/(sp2)});
filtered_jitt4 = laplace_nd(filtered_jitt3, {1, 1/(10*sp2)}, {1, 1/(sp2)});
filtered_jitt_5 = laplace_nd(filtered_jitt4, {1, 1/(sz3)}, {1, 1/(sp3)});
filtered_jitt_out = filtered_jitt_5 * K;
end

Thank you for the collaboration.
Gianni