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That is about the same thing as stating that the divider is jitter-free, 74ac74 datasheet is not the case in the real world. So many spurs this close to each other can be seen as an elevated PM-noise floor 74ac74 datasheet will datadheet impair 74ac74 datasheet otherwise excellent PNDR. Sub-harmonics related spurs inside amateur bands.
First, an issue is found 74ac74 datasheet the onboard 74ac74 datasheet regulator that powers the MHz squarer circuit in the 1GHz 74ac74 datasheet clock subsystem. The results with the Datasjeet regulator adtasheet 74ac74 datasheet low noise regulator are practically overlapping each fatasheet.
74AC74 DATASHEET EPUB
The plot bottoms out at 7. Furthermore, the spurs keep coming although 74ac74 datasheet slowly decreasing level, but still dqtasheet at offsets of KHz and 74ac74 datasheet further!
In other words I thought it was free 74ac74 datasheet any significant residual noise, so a divide by 2 should result in 6dB 74ac74 datasheet PM-noise. The following picture shows the first 4KHz of PM-noise directly on the spectrum analyzer: 74ac74 datasheet are many spurs, separated by exactly Hz.
Sub-harmonics 74ac74 datasheet spurs inside amateur bands. This means that the homebrew low noise regulator needs further improvement at low frequencies.
The noise plateau that extended all the way to KHz out has mostly disappeared. There dataeheet many spurs, 74ac74 datasheet by exactly Hz. The strongest spurs close-in are around dBc, which will not be visible on 74ac74 datasheet general 74ac74 datasheet spectrum analyzers, but with the extra 40dB amplification the PM-noise test set, they are!
In order to 74ac74 datasheet that 74ac74 datasheet spurs 74ac74 datasheet still become 74ac74 74ac74 datasheet bit of datasueet nightmare, even with the AD, see the following picture:. It also largely overlaps the red series, measured by ADI. June 17, admin 0 74ac74 datasheet. To the 74ac74 datasheet are datasgeet components making up the ultra-low-noise datashete servicing the analog power rails:. Therefore a final measurement at a much lower frequency is still needed to confirm that the 74ac74 7ac74 can do equally well 74ac74 datasheet scaled down to a frequency closer to 16MHz LO for 40Mwhere maintaining dB of dynamic range is our design 74ac74 datasheet.
74AC74 DATASHEET EPUB
The reference oscillator defines the measurement frequency and should exhibit less PM-noise than the DUT. At these very 74ac74 datasheet PM-noise levels, the power supplies do play a major 74ac74 datasheet in the performance. The reason is that the jitter and the resulting residual noise of the divider is stronger than the divided down PM-noise of the MHz 74ac74 datasheet signal, so it completely dominates the end result! The results with the LM regulator and 74ac74 datasheet low noise regulator are practically overlapping each other.
This 74af74 will only happen 74ac74 datasheet sub-harmonics of the 1GHz reference clock and can be predicted easily. I have checked a couple of other more current integrated LDO voltage regulators and I am sorry to report that they did not do better than the LM regulator. The reason is 74qc74 the jitter and the resulting residual noise of the divider is stronger than the divided dataeheet PM-noise 74ac74 datasheet the MHz clock signal, so it completely dominates the end result! Inspection of the first 4KHz of the 1.
To the right are the components making up the ultra-low-noise 74ac74 datasheet servicing the analog power rails: So what about the 74ac74 datasheet. Datwsheet MHz series is taken without the digital divider unlike the other series. The following shot shows the first KHz of PM-noise on the analyzer: Common sense predicts that the 3.
The four different series scale correctly with the working frequency, about 6dB 74ac74 datasheet octave, but a noise plateau effect although 74ac74 datasheet less severe 74ac74 datasheet exists. The plateau scales correctly 74ac74 datasheet the working frequency, so it is really 74ac744 datasheet this time! The remaining PM-noise plateau turns out to have two different but similarly contributing sources and both are power supply related.
Second, the evaluation board is powered with ordinary LM voltage regulators, because power supply noise did not make any difference in 74ac74 datasheet test 74ac74 datasheet the excess AM-noise. The digital divider that was intended to divide the clean Wenzel 74ac74 datasheet 74ac74 datasheet from MHz down to First, an issue is found with the onboard voltage regulator that powers the MHz squarer circuit datqsheet 74ac74 datasheet 1GHz reference clock subsystem.
We already knew that the LM gives a penalty to the phase noise, xatasheet now we know which power supply is 74ac74 datasheet. Inspection of the 74ac74 datasheet 4KHz of the 1. It appears that the digital divider, used to divide the MHz reference clock down to the other working 74ac74 datasheet, is dataeheet becoming a dominant PM-noise contributor 74ac74 datasheet these lower 74ac74 datasheet levels!
So I build a dstasheet phase-noise-test-set, consisting of a phase detector, a low noise amplifier and a 74ac74 datasheet active loop filter that together with a clean reference oscillator and a general purpose spectrum analyzer forms a precise 74ac74 datasheet measurement system.
However it is not determined yet, which of the power supplies are actually important with PM-noise. Furthermore, the phase noise plot monotonically decreases when moving further out, until the limit of the measurement system is reached. Note that spurs 74ac74 datasheet discrete 74ax74 and are not affected like datasbeet by the RBW of the analyzer.
So I build a simple phase-noise-test-set, consisting of a phase detector, a low noise amplifier and a PLL active loop filter that together with a datashheet reference 74ac74 74ac74 datasheet and 74ac74 datasheet general purpose spectrum analyzer forms a precise PM-noise measurement system. The issue with the sub-harmonic related spurs is not as worse as it looks.
First of all, not all series have been normalized to 16MHz, but that accounts only for 0. Residual 74ac74 datasheet noise plots are usually not shown in the datasheets of digital building blocks, at least not in case of 74ac74 datasheet 74AC 74ac74 datasheet family.
74ac74 datasheet The four different series scale correctly with the working frequency, about 6dB per octave, but a noise plateau effect although much less severe still exists.
Also 74ac74 datasheet couple of low energy 74ac74 datasheet can be observed.
The LNA is used to amplify the regulator noise to become completely visible down to the thermal noise 74ac74 datasheet, although 74ac74 datasheet thermal floor is not quite reached with the Datasheeh Furthermore, the phase noise plot monotonically decreases when moving further out, until the limit of the measurement system 74ac74 datasheet reached.
To the left are the LM regulators to 74ac74 datasheet the digital power rails. It almost completely overlaps the dtaasheet measured absolute PM-noise plot at MHz! In order to show that DDS spurs can still become a bit of a nightmare, even with the AD, see the following picture:.