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https://designers-guide.org/forum/YaBB.pl Design >> RF Design >> VCO Phase noise Discrepancy in pnoise and transient noise https://designers-guide.org/forum/YaBB.pl?num=1714177537 Message started by Hassan on Apr 26th, 2024, 5:25pm |
Title: VCO Phase noise Discrepancy in pnoise and transient noise Post by Hassan on Apr 26th, 2024, 5:25pm Hello Everyone, I am using the code below for VCO, and it is pretty standard and straightforward. I want to make sure that the noise transfer function from control voltage to phase noise is correct, as I am going to use it in my PLL. Now, when I put a purely thermal noise using a resistor on the control voltage, the output phase noise slope is -40dB/dec using PSS and Pnoise!!!! Just to clarify, I do not want to model VCO PN itself but I wanna make sure that the transfer function of noise from its control voltage to output is correct. I would appreciate any comment if you see it as helping. I am attaching both schematic and simulation results below. module vco_va(vin, voutp, voutn); input vin; output voutp , voutn; electrical vin, voutp, voutn; parameter real amp = 0.5; parameter real center_freq = 20G; parameter real vco_gain = 1G; parameter integer steps_per_period = 32; parameter real DC_val = 1; real phase; real inst_freq ; analog begin inst_freq = center_freq + vco_gain * (V(vin)-1.25); phase = idtmod(inst_freq, 0,1); $bound_step (1.0 / (steps_per_period*inst_freq)); V(voutp) <+ amp * sin (2*`M_PI*phase) + DC_val; V(voutn) <+ -1*amp * sin (2*`M_PI*phase) + DC_val; end endmodule |
Title: Re: VCO Phase noise Discrepancy in pnoise and transient noise Post by smlogan on May 27th, 2024, 6:17pm Dear Hassan, In case you have not determined the root cause of your observed -40 dB/decade phase noise characteristic, I believe the issue is you are applying frequency noise - not phase noise - by including the noisy 1K resistor in series with the control voltage input. In essence, the control voltage input modulates frequency. Hence, the slope of a flat noise source applied to the control voltage of the VCO will result in -40 dB/decade phase noise slope - not -20 dB/decade. Shawn |
Title: Re: VCO Phase noise Discrepancy in pnoise and transient noise Post by Hassan on Jun 3rd, 2024, 1:16pm Hello Shawn, Thanks for your answer. I am still looking for an answer to this question. As far as I know, when I have white noise, the integral of it will have a spectrum with a slope of -20dBc/dec since its spectrum is simply multiplied by 1/s^2. I verified this using transient noise simulation, showing a -20dBc/dec slope. Please take a look at image below from "Phase Noise and Jitter in CMOS Ring Oscillators" paper. |
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