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Design >> Analog Design >> Jitter in VCO
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Message started by ram on Aug 17^th, 2004, 5:36am

Title: Jitter in VCO
Post by ram on Aug 17^th, 2004, 5:36am

Hi,

I want to know jitter value of my ring oscillator. I have designed the circuit using hspice. How can I measure the jitter through hspice I mean what should be test setup to measure it. Please guide me on this.

Thanks

ram

Title: Re: Jitter in VCO
Post by ywguo on Aug 18^th, 2004, 5:33am

Ram,

It is difficult to simulate the jitter of VCO in HSPICE.

I used to measure the jitter of VCO by adding a small series resistor on power supply. But it just introduce a ripple of the same period as the VCO. So the period of VCO is still constant.

I also tried to measure the jitter by tuning the power supply a little, say 100mV. Then I measure the difference of the period (T_p1) before tuning and the period (T_p2) after tuning.

T_jitter = T_p1 - T_p2

Obviously it is not accurate because we don't know the amplitude of power supply noise and ground noise.

So the problem is modeling the substrate noise and other inteference. The real jitter of a PLL/VCO is very senstive to its environment, including swithing noise of digital circuit, SSN noise of pads, even electromagnetic radiation. The real jitter is difficult to predict because the huge digital circuit is not controled by the circuit designer who design the PLL. :(

Best regards,
Yawei

Title: Re: Jitter in VCO
Post by ram on Aug 18^th, 2004, 11:14pm

Yawai,

Thanks for the guidance.

I want to know how to convert this Tjitter to rms jitter spec.

Thanks again.

Regards
Ram

Title: Re: Jitter in VCO
Post by ywguo on Aug 22^nd, 2004, 9:20pm

Ram,

The T_jitter is just a crude estimation. I don't know how to convert it to rms jitter. sorry.

Best regards,
Yawei