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weird phenomenon of vco phase noise simulation? (Read 2947 times)
lwzunique
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weird phenomenon of vco phase noise simulation?
Mar 06th, 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?

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cheap_salary
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Re: weird phenomenon of vco phase noise simulation?
Reply #1 - Mar 6th, 2017, 9:05pm
 
Do you surely specify correct harmonic for divide-by-2 case ?
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lwzunique
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Re: weird phenomenon of vco phase noise simulation?
Reply #2 - Mar 6th, 2017, 9:16pm
 
cheap_salary wrote on Mar 6th, 2017, 9:05pm:
Do you surely specify correct harmonic for divide-by-2 case ?

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.
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cheap_salary
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Re: weird phenomenon of vco phase noise simulation?
Reply #3 - Mar 6th, 2017, 10:24pm
 
Wrong, as you are always.
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lwzunique
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Re: weird phenomenon of vco phase noise simulation?
Reply #4 - Mar 7th, 2017, 2:34am
 
cheap_salary wrote on Mar 6th, 2017, 10:24pm:
Wrong, as you are always.

could you please show me how to do, thank you.@cheap_salary
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lwzunique
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Re: weird phenomenon of vco phase noise simulation?
Reply #5 - Mar 7th, 2017, 3:18am
 
cheap_salary wrote on Mar 6th, 2017, 10:24pm:
Wrong, as you are always.

at last, I find the reason, relative harmonic should be 2, thank you!@cheap_salary.
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cheap_salary
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Re: weird phenomenon of vco phase noise simulation?
Reply #6 - Mar 7th, 2017, 3:39am
 
lwzunique wrote on Mar 7th, 2017, 3:18am:
cheap_salary wrote on Mar 6th, 2017, 10:24pm:
Wrong, as you are always.

at last, I find the reason, relative harmonic should be 2, thank you!@cheap_salary.
Correct.

Relative harmonics have to be:
2 for VCO
2 for VCO_Buffer
1 for CML_DIV2.
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