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https://designers-guide.org/forum/YaBB.pl Simulators >> RF Simulators >> VerilogA erases clock phase noise with PNOISE https://designers-guide.org/forum/YaBB.pl?num=1194372415 Message started by adam_eaz on Nov 6th, 2007, 10:06am |
Title: VerilogA erases clock phase noise with PNOISE Post by adam_eaz on Nov 6th, 2007, 10:06am I am applying a differential clock signal as an input which has some phase noise, and I am producing a differential clock signal that has a fixed pulse width. The problem is that the resulting signal doesn't have any phase noise. The PSS analysis does work, with the correct wave forms produced. `include "constants.vams" `include "disciplines.vams" module xosc10b_amfilter (inp, inm, outp, outm); input inm, inp; inout outm, outp; voltage inm, inp, outp, outm, vgain; parameter real vswing=1; parameter real td=50p; parameter real tt=50p; parameter real delaytime=6.4300412n; real vtime, vmin, vmax; integer actNow, out, reset; analog begin actNow=0; vmin=-vswing/2; vmax=vswing/2; @(cross(V(inp,inm),1)) actNow=1; vtime= idt(1/delaytime, 0, actNow); out = vtime<1; V(outp,outm) <+ transition(out ? vmax : vmin, td, tt); end endmodule |
Title: Re: VerilogA erases clock phase noise with PNOISE Post by Stefan on Nov 6th, 2007, 10:17am You should (dramatically!) increase your analog accuracy-settings and specify the tolerance of the @cross statement. td and tt are far too high with 50 ps. This would kill nearly all phasenoise characteristics. Just think about an oscillator with a center frequency of 2.4GHz for Bluetooth for example. Specifications for the LO demand for -105 dBc/Hz at 1 Mhz offset from the carrier which leads to a corresponding Jitter (standard deviation) of around 48 fs. It's for sure that an accuracy of several ps simply swallows this noise ... |
Title: Re: VerilogA erases clock phase noise with PNOISE Post by adam_eaz on Nov 6th, 2007, 11:50am I tried your suggestion of increasing the analog accuracy and cross point. I also changed the rise time to 200ps, but I am still getting the same result which is -6.4k dBc for all frequencies. Any other suggestions? Adam |
Title: Re: VerilogA erases clock phase noise with PNOISE Post by Stefan on Nov 6th, 2007, 1:35pm You should tighten the rise time, not raising it. It might be best to provide the whole setup, including the model for the noisy osc. I might be able to check it tomorrow morning (local time central europe). Regards, Stefan |
Title: Re: VerilogA erases clock phase noise with PNOISE Post by Frank Wiedmann on Nov 6th, 2007, 11:29pm See http://www.designers-guide.org/Forum/YaBB.pl?num=1189658426/5#5. |
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