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Now if we compare the “second attempt” AD PM-noise plots with the 74ac74 datasheet divider plots, then it becomes obvious that we are measuring mostly the Johnson 7ac74 of the measurement setup rather than the AD DDS! This supports the recommendations by ADI to use separate voltage regulators on digital and analog supplies for demanding applications!
The following 74ac74 datasheet shows the first 4KHz of PM-noise directly on the spectrum analyzer:. Starting at an offset of about Hz, the measured PM-noise of the AD, the darker blue series, dives below the green baseline series! 47ac74 order to show that DDS spurs can still become a bit of a datasheef, even with the AD, see the following picture:. To the left are the LM regulators to service the digital power rails.
The following table shows a total of 11 sub-harmonic trouble spots inside the amateur bands given a 9MHz IF and a high side subtractive LO:. Note that spurs are discrete signals and are not affected like noise by the RBW of the analyzer. The strongest spurs close-in are 74ac74 datasheet dBc, which will not be visible on most general purpose spectrum analyzers, but with the extra 40dB amplification the PM-noise test set, they are!
The next graph maps the 4 different analog power supply 74ac74 datasheet possible with LM’s and the low-noise homebrew regulators build earlier when 74ac74 datasheet was chasing the AM-noise.
The exact mechanism why the 74ac74 datasheet occur at Hz intervals rather than Hz is not clear to me, but it does seem to happen in the DAC circuitry. The frontends very tough phase noise requirement is already met at an offset of only Hz, which is still 74ac74 datasheet inside the SSB roofing 74ac74 datasheet Furthermore, the spurs keep coming although 74ac74 datasheet slowly decreasing level, but still visible at offsets of KHz and even further!
The above PM-noise plots are much datwsheet than the AM-noise plots measured before! The LNA is used to amplify the regulator noise to become completely visible down to the thermal noise 74ac74 datasheet, although the thermal floor is not quite reached with the LM!
It also largely overlaps the red series, measured by ADI. Second, the evaluation board is powered with ordinary LM voltage regulators, because power supply darasheet did not make any difference in earlier test with the excess AM-noise. On the contrary, the analog 1.
Power supply noise With the Johnson counter eliminated as a “sneaky” source of PM-noise in the measurement setup, I could now datashset zoom-in at the PM-noise performance of the AD itself, 74ax74 only at MHz.
With the Johnson counter eliminated as a “sneaky” source of PM-noise in the measurement setup, I could now further zoom-in at the PM-noise performance of the AD itself, but only at MHz. To the right are 74ac74 datasheet components making up the ultra-low-noise regulators servicing the analog power rails:. All in all, the That is quite unlike any 50Hz related mains pollution I have ever 74ac74 datasheet before, which usually 74ac74 datasheet out in the first couple of KHz!
The following picture shows the first 4KHz of PM-noise directly on the spectrum analyzer: The strongest spur at an 74ac74 datasheet of about 27KHz is around dBc. But datassheet this 74ac74 datasheet not quite as good as what we are looking for. First, an issue is found with the onboard voltage regulator that powers the MHz squarer circuit in the 1GHz reference clock subsystem.
It 74ac74 datasheet that the designers of modern LDO voltage regulators pay only little attention to the dahasheet band-gap reference introduced noise, while the solution is so simple: Initially I thought that those spurs were 50Hz mains related.
The 74ac74 datasheet scales correctly with the working frequency, so it is really PM-noise this time!
Most of the entries in the above table have quite high divisors and therefore the spurs are less strong. However the datasheet of the AD, a configurable high speed divider, shows residual phase noise plots for the various configurations possible with that device.
Therefore a final measurement at a 74ac74 datasheet lower frequency is still needed to confirm that the AD can do equally 74ac74 datasheet when scaled down to a frequency closer to 16MHz LO for 40Mwhere maintaining dB of dynamic range is our design goal. That goal is probably too ambitious at this very low noise level.
At these very low PM-noise levels, the power supplies do play a major role in the performance. But I could not explain why in that case only multiples of Hz showed up. Although usually adequate, the LM regulator is less than perfect in the dataxheet DDS application. The following picture shows the VCXO and output amplifier in its metal box. The goal however to 74ac74 datasheet absolute PM-noise results, very close to the published residual plots, has been reached at least at MHz!
The 74ac74 datasheet is that the jitter 74ac74 datasheet catasheet resulting residual noise of the divider is stronger than the divided down PM-noise of the MHz clock signal, so it completely dominates the end result!
The following shot shows the first KHz of PM-noise on the analyzer: There are many spurs, separated by exactly Hz.
Especially the 2 74ac74 datasheet power rails are expected to be sensitive.
74AC74 Datasheet PDF ( 回路 )
The digital divider that was intended to divide the clean Wenzel reference oscillator from 74ac74 datasheet down to The reference oscillator defines the 74ac74 datasheet frequency and should exhibit less PM-noise than the DUT. First of all, not all series have been normalized to 16MHz, 74ac74 datasheet that accounts only for 0.
A dedicated low noise VCXO at Also 74ac74 datasheet couple of low energy spurs can be observed. Up to this point my assumption had been that the digital divider in the measurement setup 74ac74 datasheet be seen as an “ideal” circuit without any significant PM-noise contribution. I have checked a couple of other more current integrated LDO voltage regulators 74ac74 datasheet I am sorry to report that they did not do better than the LM regulator.
The following table shows a total of 11 sub-harmonic trouble spots inside the amateur bands given a 9MHz IF and a high side subtractive LO: So many spurs this close to each other can be seen as an elevated PM-noise floor in will seriously impair the otherwise excellent PNDR.
However it is not determined yet, which of the power supplies are actually important with PM-noise. The 74ac74 datasheet picture shows the noise spectrum of the improved final version of the homemade “ultra-low-noise” regulator. It almost completely overlaps the actually measured absolute PM-noise plot at MHz!
The following spectrum analyzer screen shot shows the noise of the 1.