What is Normalized Phase Noise?
For example, in http://www.ti.com/lsds/ti/clock-and-...-products.page , this number is in dBc/Hz and ranges between -226 and -231.
Even more confusing here: http://www.analog.com/en/parametricsearch/10713 where they write: "Normalized Phase Noise (dBc/rtHz) (dBc/Hz)". Wtf? Hz or rtHz? Makes a big difference ...
Usually phase noise is denoted in dBc/Hz at different offset frequencies. Does "Normalized Phase Noise" mean that the frequency domain shape is just normalized to one over the operation bandwidth? In other words, the integral over the actual phase noise curve equals the normalized phase noise times the bandwidth?
If this is the case, is there a direct way to deduce jitter from this number?
Using the relation SNR = 20*log(1/(2*pi*fc*sigma) and sigma = sqrt(10^(A/10))/2/pi/fc
I arrive at the nice equation:
PN = -SNR - 10log(2B)
(where A is just PN + 10*log(2B) with PN the normalized phase noise in dBc/Hz and 2B the operation bandwidth (factor of 2 because phase noise curve is double sided)
which tells me for example that if I want an SNR of 50dB (due to phase noise) and a bandwidth of 400 MHz I would need a PLL with -139 dBc/Hz?
But this does not match the available numbers (in the range of -230dBc)
See pp.29-30 of http://cds.linear.com/docs/en/datasheet/6948f.pdf
Thank you!
However, this seems like a completely useless metric to me because it just gives a hint about one single point at the phase noise figure L(f).
Suppose I need 100fs RMS jitter at 2 GHz (i.e., integrated L(f)), how would this normalized phase noise metric help me to find the right product?
No.
In your case, Normalized In-Band 1/f Noise is not defined.
There is no option other than ignoring 1/f Noise.
So worst case value of Lout inside PLL_BW should be estimated via Lnorm.
Again see Figure 14 at page-30 of http://cds.linear.com/docs/en/datasheet/6948f.pdf
Again, there is no option other than ignoring 1/f Noise.
So you have to estimate RMS_Jitter value roughly by the following.
Lout = Lnorm + 10*log10(fpfd) + 20*log10(frf/fpfd)
RMS_Jitter = sqrt(2 * 10**(Lout/10) * PLL_BW) / (2*pi*frf)
frf = 2GHz
fpfd = ?
PLL_BW = ?
This is really helpful and great, thanks!
To make sure: PLL_BW is not the loop BW of the PLL or so but the actual signal bandwidth of the receiver? And fpfd is the frequency at the phase detector which is supposed to be the reference clock?
What I am still slightly confused: This formula assumes a constant frequency spectrum for Lout .... However, L(f) consists to first order of multiple log-line segments (e.g. 1-300 Hz, 300 Hz-10kHz, 10 kHz - 30 Mhz ...). To my understanding, Lout just estimates the middle "flat" piece. Is it really reasonable to neglect the rest? What errror can be typically expected?
I fully understand your confusion. dBc/Hz was the standard for decades, then some yuppie clueless engineers decided to start using other nomenclatures, and now confusion reigns. just chalk it up to their arrogance of not standing on the shoulders of giants.
No.
It has to be loop BW in close loop state of PLL.
If there is no reference divider, fpfd=fref.
See Figure 13 at page-25 of http://cds.linear.com/docs/en/datasheet/6948f.pdf
Yes.
It assumes constant Lout over PLL_BW.
See "LTC6948-4 Phase Noise(fRF=6236MHz)" at page-1 of http://cds.linear.com/docs/en/datasheet/6948f.pdf
It should be reasonable estimation as far as 1/f noise is not very large.
Again see "LTC6948-4 Phase Noise(fRF=6236MHz)" at page-1 of http://cds.linear.com/docs/en/datasheet/6948f.pdf
See page-9 of http://cds.linear.com/docs/en/datasheet/6948f.pdf
See Figure 8 at page-20 http://www.st.com/web/en/resource/te...DM00108283.pdf
Ok, great, thanks again!
Let me me show the concrete example where I see the inconsistency:
Different noise levels are annotated, along with the loop bandwidth (~450kHz). I know the output frequency is frf=2100 MHz. The PLL is the ADF4153. I am very confident that the reference clock is fpfd=737.28 MHz. According to the datasheet, the input reference can be divided by integers between 1,...,15 (4 bit).
Based on different methods (e.g. https://www.jitterlabs.com/support/calculators/ or the MATLAB script http://www.mathworks.com/matlabcentr...nt/Pn2Jitter.m) I can obtain the jitter by integration:
f_Hz = [ 0 100 1000 10e3 100e3 1e6 10e6 30e6 1e9 ];
g_dBc1Hz = [ -77.44 -77.44 -81.42 -87.04 -111.83 -138.26 -159 -169 -200 ];
Jitter = Pn2Jitter(f_Hz, g_dBc1Hz, 2.1e9) = 778fs RMS
But then, using the normalized phase noise along with the calculations you suggest:
Lnorm = -220; % from the datasheet of ADF4153
frf = 2.1e9;
fpfd = 737.28e6/15; % 15 is maximum division according to datasheet
BW_PLL = 450e3; % from the plot
Lout = Lnorm + 10*log10(fpfd) + 20*log10(frf/fpfd);
sigma = sqrt(2 * 10^(Lout/10) * BW_PLL) / (2*pi*frf) = 215.36fs RMS
This is far off from the calculations above ...
inv_db10 = @(x) 10.^(x/10); frf = 2100e6; % [Hz] Loop_BW = 7e3; % [Hz] Lout = g_dBc1Hz(3); RMS_Jitter = sqrt(2 * inv_db10(Lout) * Loop_BW) / (2*pi*frf) / 1e-15;
Lout = -81.42[dBc/Hz]
RMS_Jitter = 761.49[fsec]
This value is fairly close to result of "Pn2Jitter(f_Hz, g_dBc1Hz, 2.1e9)".
Do you surely read datasheet of ADF4153 ?
http://www.analog.com/media/en/techn...ts/ADF4153.pdf
It can never be.
Surely read datasheet of ADF4153.
Frequency range of REFIN is guranteeded from 10MHz~250MHz.
This means fpfd=49.152MHz.
It can never be.
Surely read datasheet of ADF4153.
Maximum fpfd of ADF4153 is 32MHz.
It can never be.
Loop_BW of http://snag.gy/1zAbZ.jpg is less than 7kHz.
And line of LoopBW is located at 0.5kHz in http://snag.gy/1zAbZ.jpg
Why ?
How do you get this http://snag.gy/1zAbZ.jpg ?
Show me true and correct values of the followings.
frf ?
fpfd ?
Loop_BW ?
Charge Pump Current ?
At least, fpfd can never be 737.28e6/15=49.152MHz.
And Loop_BW can also never be 450kHz.
Attached figure is a result of the following code
db10 = @(x) 10 * log10(x); db20 = @(x) 20 * log10(x); inv_db10 = @(x) 10.^(x/10); inv_db20 = @(x) 10.^(x/20); Lnorm = -220; % [dBc/Hz], Normalized Phase Noise Floor L1_f = -114; % [dBc/Hz], Normalized 1/f Noise, Measured at 10kHz offset, Normalized to 1GHz frf_meas = 1000e6; %[Hz] foffset_meas = 10e3; %[Hz] frf = 2.1e9; %[Hz] fpfd = 0.2e6; %[Hz] % plot the results (except at DC) semilogx(f_Hz(2:end), g_dBc1Hz(2:end), 'r', 'Linewidth', 2) Lout_1 = ( Lnorm + db10(fpfd) + db20(frf/fpfd) ) * ones( size( f_Hz(2:end) ) ); semilogx(f_Hz(2:end), Lout_1, 'g', 'Linewidth', 2) Lout_2 = L1_f + db10(foffset_meas./f_Hz(2:end)) + db20(frf/frf_meas); semilogx(f_Hz(2:end), Lout_2, 'c', 'Linewidth', 2) Lout_3 = db10( inv_db10(Lout_1) + inv_db10(Lout_2) ); semilogx(f_Hz(2:end), Lout_3, 'y', 'Linewidth', 2)
Again How do you get this http://snag.gy/1zAbZ.jpg ?
Show me true and correct conditions of http://snag.gy/1zAbZ.jpg