Why LC VCO Multiphase Clocking for High-speed SerDes?

[@RushabhkumarPatel-bo3qz]

Hi CC, Thank you for such a great content. Its a gold mine and very upto date with industry rightnow. I am curious why don't people directly use DLL to generate 64 phases instead they go on putting PI after DLL. Is it due to accuracy? Also, CC if you can make a video on clock distribution techniques. That would be great.

[@abhiruplahiri1]

I remember around 10yrs doing injection locking into ring oscillator from 2phase LC VCO for quadrature phase gen. Another way to generate quadrature phase is using polyphase (RC-CR) filter, which I made for a product to provide clocks to IQ mixer in wireless receivers. Ofcourse, DLL is quie popular especially in serdes for providing multi-phases for PI.

[@circuitimage]

Hi Abhirup, thank you so much for the feedback. Correct. 20 years ago. I designed both injection locking & polyphase filters in RF, not SerDes. That might be okay for a narrowband RF, but not quite easy to tune at a wideband SerDes. :)

[@abhiruplahiri1]

@@circuitimage completely agree CC. Hope to see high linearity PI video in the near future.

[@circuitimage]

@@abhiruplahiri1 thank you so much for the reminder. I'll do the high-linearity PI video for sure. :)

[@mahmoudabdelwahab9519]

Could you please make a video on measuring and calibrating the multiphase outputs with a small phase spacing accuracy such as the femtosecond range? Relying on XOR and then taking the average, I think it might not be sufficient to get a very fine time resolution

[@circuitimage]

Hi Mahmoud, thank you so much for the suggestion. Sure. I'll do and this phase accuracy calibration is very critical at a high-speed clock.