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Measurements >> Phase Noise and Jitter Measurements >> phase noise measurement
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Message started by kioas2003 on Jul 3^rd, 2003, 11:25pm

Title: phase noise measurement
Post by kioas2003 on Jul 3^rd, 2003, 11:25pm

Currently, I 'm doing the phase noise measurement for an integer-N frequency synthesizer (Giga Hz range).

1)Can we calculate the actual jitter at the output of the vco by measuring the jitter at the output of the divider?
1a)If there is the case, what is the relationship between them?
1b) How to convert the jitter information to phase noise infomation?
2)Would the power of the vco output affect the phase noise measurement result if the measurement was done at the output of the vco buffer using a spectrum analyzer ?

The reason why I measuring the jitter at the output of the divider as we're having diffficulties in measuring the phase noise directly at the output of the vco due to termination problem.

I hope someone can help me on these issues.

Title: Re: phase noise measurement
Post by fast locker on Jul 7^th, 2003, 1:32pm

Hi, kioas2003,

Hopefully this helps.

kioas2003 wrote on Jul 3^rd, 2003, 11:25pm:

How do you do the jitter measurement? Is your result in degrees or seconds? Theoretically, suppose your division ratio is N, then your results in degrees at the output of the divider should be 1/N of the result at the output of the VCO.

Quote:

1b) How to convert the jitter information to phase noise infomation?

The jitter infomation is only related to the integrated phase noise information in my understanding. In other words, you can not get a spot phase noise performance, ie, how many dBc/Hz 100KHz offset from the carrier from the jitter measurement results. There is an equation:

jitter in radians = sqrt(2*integration(L(f), df, f1, f2))

L(f) is the SSB phase noise curve in dBc/Hz. f1 and f2 are the application specified frequency range.

Quote:

2)Would the power of the vco output affect the phase noise measurement result if the measurement was done at the output of the vco buffer using a spectrum analyzer ?

In the designing stage, yes, the VCO output power affects the phase noise performance. We should always maximize the VCO power. In the measurement stage, no, the phase noise result will not be affected by the buffer. Neither will it be affacted by how much power is coupled to the spectrum analyzer because the carrier and noise power are reduced by the same ratio and you are measuring the relative difference (dBc).

Quote:

The reason why I measuring the jitter at the output of the divider as we're having diffficulties in measuring the phase noise directly at the output of the vco due to termination problem.

I hope someone can help me on these issues.

Title: Re: phase noise measurement
Post by kioas2003 on Jul 7^th, 2003, 7:18pm

Thank u for your reply fast lockers.

1) We're doing the jitter measurement using the high frequency oscillator. We get the cycle to cycle jitter and period jitter in pS range. Which jitter information r u referring to. Can the relationship given in your reply apply to both cycle to cycle and period jitter as well?

2)In the article writtern by Ken Kundert named "predicting the phase noise and jitter of pll-based frequency synthesizer" page number42, there is also a relationship there but it is in jitter instead of degree. The equation is Jvco=J[FD]/sqrt(N).
From this equation, we convert the jitter info at the vco output is much less than what we get from your equation?

3)For gigaherts pll, what is the commercial spec for the jitter at the output of vco in term of degree(radian)?

4)As we know the phase noise obtained from spectrum analyser consists of two parts namely the amplitude noise,a(t) and phase noise, p(t). By instinctively thinking, when the measured power reducing, only the
a(t) would be reducing and p(t) remained the same, I don't know whether the above statement is true or not?
If it is true, so the total phase noise in term dBc/Hz would be increased when the power of the vco reducing in the measurement stage as the p(t) remained the same. Pls correct me, if I'm wrong.

Thanks and regards.