PLL Verification RAK - Total Phase Noise

Dear JoJakNap,

JoJakNap said:

Are these two correct? And if so can someone explain why?

I apologize for my late response! I took some time to study the relevant sections of the PLL Verification RAK you referred to and assembled a response to each of your questions I hope I understood them correctly!

To answer each question, I had to extract the data from the plots shown in the RAK in order to perform the analysis. A summary of my responses and the analysis are attached. The attached file has a reduced resolution as Forum guidelines prevent me from uploading files over about 1 MB.  If you have any trouble reading it, the full resolution file may be found at:

Once, again, I cannot include a non-Cadence link in my response, but to allow you to access the note if you are interested, you may copy and append the following into your browser following the usual internet prefix.

1drv.ms/

b/s!AnM-GsAEZPoSsBllFBcFZdlaortS?e=cxwds0

Let me know if you have any questions or comments JoJokNap, and I hope this is not too late to be useful to you!

Shawn

PLL_verification_WS_rak_questions_121723v1p0.pdf

By the way your answer and curious by JoJakNap question, so i took a look at page 59 (Action 78).I think there is a wrong comment here about VCO phase noise. the correct one shoule be " the injected VCO phase noise is high pass filtered ....." not low pass

Dear Binhngo1210,

Binhngo1210 said:

I think there is a wrong comment here about VCO phase noise. the correct one shoule be " the injected VCO phase noise is high pass filtered ....." not low pass

Yes. The statement you refer to on page 59 is rather misleading. The author "somewhat" corrects his or her statement beneath the second figure of Action 78 on page 60 describing the action of the closed loop transfer function for the DSM noise (see Figure 1).

However, in my opinion, neither statement really enhances one's understanding of the impact of the noise of each of the phase-locked loop components on the total output noise of the phase-locked loop. If I had to re-write the statements, I might include something like the following:

The noise of a phase-locked loop's reference oscillator and its individual components each contribute to its total output noise. The manner in which the reference oscillator noise and each component's noise contribute differ as a result of where the noise of each is injected (outside or within the phase-locked loop).

Further, the contribution of each noise source is dependent on the loop gain of the phase-locked loop (of which the individual components play a major role). In other words, the contribution of a given phase-locked loop component to the output noise is a function of both the noise of that component and the overall loop gain.

The reference oscillator noise contribution to the total output noise is conceptually and mathematically easiest to understand and compute. Its noise serves as an input to the phase-locked loop and hence its filtered by the transfer function of the phase-locked loop itself. Since the transfer function of a phase-locked loop is low pass in nature with potential transfer function peaking, the noise contribution of the reference oscillator to the output noise is the reference oscillator noise filtered by the phase-locked loop transfer function.

Since the phase detector and any potential loop filter are contained in the forward loop path of the phase-locked loop, each of their noise sources are filtered by the closed-loop transfer function of the phase-locked loop.

The VCO noise consists of two components: the innate VCO noise (as a standalone component); and the added signal and noise introduced into its control voltage input by the output of the phase-detector, loop filter and divider. For frequencies where the loop gain is large, the control voltage input will cancel the VCO innate noise and match the noise of the reference oscillator. However, as the loop gain becomes smaller at higher frequencies, it will not be able to totally match the reference oscillator noise and the phase-locked loop output noise will start to reflect the innate noise of the VCO. Intuitively, this suggests the noise contribution of the VCO to the total output noise consists of the highly attenuated VCO noise at low frequencies that gradually increases to the innate VCO noise as the loop gain approaches unity (i.e., the closed loop transfer function bandwidth). Therefore, the VCO noise transfer function is high pass in nature whose characteristic is determined by the inverse of the low pass phase-locked loop transfer function.

The DSM noise is effectively injected at the same point as the VCO output node within the phase-locked loop. As such, its noise contribution to the total output noise is also filtered by the inverse of the low pass phase-locked loop transfer function - which is high pass in nature but NOT as the text indicates "high pass filtered by the closed-loop PLL transfer function to the output phase noise".

I hope this is consistent with your thinking Binhngo1210. Let me know if it is not!

Shawn

Figure 1

Page 60 of reference [1]

[[1] "PLL Verification Rapid Adoption Kit (RAK)", Product Version IC 6.1.8, MMSIM 21.1, XCELIUM 21.09 May, 2022

Dear Binhngo1210,

Binhngo1210 said:

I think there is a wrong comment here about VCO phase noise. the correct one shoule be " the injected VCO phase noise is high pass filtered ....." not low pass

Yes. The statement you refer to on page 59 is rather misleading. The author "somewhat" corrects his or her statement beneath the second figure of Action 78 on page 60 describing the action of the closed loop transfer function for the DSM noise (see Figure 1).

However, in my opinion, neither statement really enhances one's understanding of the impact of the noise of each of the phase-locked loop components on the total output noise of the phase-locked loop. If I had to re-write the statements, I might include something like the following:

The noise of a phase-locked loop's reference oscillator and its individual components each contribute to its total output noise. The manner in which the reference oscillator noise and each component's noise contribute differ as a result of where the noise of each is injected (outside or within the phase-locked loop).

Further, the contribution of each noise source is dependent on the loop gain of the phase-locked loop (of which the individual components play a major role). In other words, the contribution of a given phase-locked loop component to the output noise is a function of both the noise of that component and the overall loop gain.

The reference oscillator noise contribution to the total output noise is conceptually and mathematically easiest to understand and compute. Its noise serves as an input to the phase-locked loop and hence its filtered by the transfer function of the phase-locked loop itself. Since the transfer function of a phase-locked loop is low pass in nature with potential transfer function peaking, the noise contribution of the reference oscillator to the output noise is the reference oscillator noise filtered by the phase-locked loop transfer function.

Since the phase detector and any potential loop filter are contained in the forward loop path of the phase-locked loop, each of their noise sources are filtered by the closed-loop transfer function of the phase-locked loop.

The VCO noise consists of two components: the innate VCO noise (as a standalone component); and the added signal and noise introduced into its control voltage input by the output of the phase-detector, loop filter and divider. For frequencies where the loop gain is large, the control voltage input will cancel the VCO innate noise and match the noise of the reference oscillator. However, as the loop gain becomes smaller at higher frequencies, it will not be able to totally match the reference oscillator noise and the phase-locked loop output noise will start to reflect the innate noise of the VCO. Intuitively, this suggests the noise contribution of the VCO to the total output noise consists of the highly attenuated VCO noise at low frequencies that gradually increases to the innate VCO noise as the loop gain approaches unity (i.e., the closed loop transfer function bandwidth). Therefore, the VCO noise transfer function is high pass in nature whose characteristic is determined by the inverse of the low pass phase-locked loop transfer function.

The DSM noise is effectively injected at the same point as the VCO output node within the phase-locked loop. As such, its noise contribution to the total output noise is also filtered by the inverse of the low pass phase-locked loop transfer function - which is high pass in nature but NOT as the text indicates "high pass filtered by the closed-loop PLL transfer function to the output phase noise".

I hope this is consistent with your thinking Binhngo1210. Let me know if it is not!

Shawn

Figure 1

Page 60 of reference [1]

[[1] "PLL Verification Rapid Adoption Kit (RAK)", Product Version IC 6.1.8, MMSIM 21.1, XCELIUM 21.09 May, 2022

thanks for detailed words, hope it helps for other members too 

Dear Binhngo1210,

Binhngo1210 said:

for detailed words,

I am just amazed you managed to read them all!

I also hope it is instructive for others with an interest. Thank you Binhngo1210!

Shawn