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https://designers-guide.org/forum/YaBB.pl Measurements >> Phase Noise and Jitter Measurements >> weird phenomenon of vco phase noise simulation? https://designers-guide.org/forum/YaBB.pl?num=1488861393 Message started by lwzunique on Mar 6th, 2017, 8:36pm |
Title: weird phenomenon of vco phase noise simulation? Post by lwzunique on Mar 6th, 2017, 8:36pm Hi everyone! I came across a weird question about VCO phase noise simulation. The circuit structure is as shown below, VCO+ VCO_BUFFER + DIV_BY_2(CML). when doing pss+pnoise simulation of single VCO or VCO+ VCO BUFFER, the phase noise results is as shown in case 1. VCO output phase noise is -116dBc/Hz@1MHz, and the buffer's output is a little bit worse. the weird thing is ,when I added div_by_2 block, the phase noise of VCO_OUTPUT AND BUFFER’s output decline rapidly. -93dBc/Hz@1Mhz,-60dBc/Hz@1MHz,repectively. but the div_by_2's output signal's phase noise is -122dBc/Hz@1MHz. [img][/img] why? |
Title: Re: weird phenomenon of vco phase noise simulation? Post by cheap_salary on Mar 6th, 2017, 9:05pm Do you surely specify correct harmonic for divide-by-2 case ? |
Title: Re: weird phenomenon of vco phase noise simulation? Post by lwzunique on Mar 6th, 2017, 9:16pm cheap_salary wrote on Mar 6th, 2017, 9:05pm:
the frequency of divide-by-2 is 2.119 GHz, so I set the beat frequency equals to 2.119 GHz in pss setting, and number of harmonic is 15. but the result is almost the same. |
Title: Re: weird phenomenon of vco phase noise simulation? Post by cheap_salary on Mar 6th, 2017, 10:24pm Wrong, as you are always. |
Title: Re: weird phenomenon of vco phase noise simulation? Post by lwzunique on Mar 7th, 2017, 2:34am cheap_salary wrote on Mar 6th, 2017, 10:24pm:
could you please show me how to do, thank you.@cheap_salary |
Title: Re: weird phenomenon of vco phase noise simulation? Post by lwzunique on Mar 7th, 2017, 3:18am cheap_salary wrote on Mar 6th, 2017, 10:24pm:
at last, I find the reason, relative harmonic should be 2, thank you!@cheap_salary. |
Title: Re: weird phenomenon of vco phase noise simulation? Post by cheap_salary on Mar 7th, 2017, 3:39am lwzunique wrote on Mar 7th, 2017, 3:18am:
Relative harmonics have to be: 2 for VCO 2 for VCO_Buffer 1 for CML_DIV2. |
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