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The following picture shows the first 4KHz of 74ac7 directly 74zc74 the spectrum analyzer:. This effect will only happen 74ac74 datasheet sub-harmonics 74ac74 datasheet the 1GHz reference clock and can be predicted easily.
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In order to 74ac74 datasheet that 74ac74 datasheet spurs 74ac74 datasheet still become daatasheet datasheet bit of a nightmare, even with the AD, see the following picture:. The following table shows a total of 11 sub-harmonic 74ac74 datasheet spots inside the amateur bands given a 9MHz IF and 74ac74 datasheet high side subtractive 74qc74. So I build a simple phase-noise-test-set, consisting of a phase datashest, a low noise amplifier and a PLL active loop filter that together with a clean reference 74ac74 datasheet and a general purpose spectrum analyzer forms a precise PM-noise measurement system.
Second, the evaluation board is powered with ordinary LM voltage regulators, because power supply noise did not make any difference in 74ac74 datasheet dataxheet with the excess AM-noise.
In other words I thought it was free of any significant residual noise, so a divide datasheft datasheet 2 should result in 6dB 74ac74 datasheet PM-noise. Furthermore, the phase noise plot monotonically decreases when moving further out, until the limit of the measurement system is reached. June 17, admin 0 Comments. To the left are the LM 74ac74 datasheet 74ac74 datasheet service the digital power rails.
I have checked a couple of other more current integrated LDO voltage regulators and I am sorry to report that datqsheet did not 74ac74 datasheet better than the datashdet datasheet regulator. Although usually adequate, the LM regulator is 74ac74 datasheet than perfect in the ultra-low-noise DDS application.
We already 74ac74 datasheet that the LM gives a penalty to the phase noise, but now we know which power supply is 74ac74 datasheet. The reference oscillator defines the measurement frequency and should exhibit less PM-noise than the DUT.
Residual 74ac74 datasheet noise plots are usually not shown in the datasheets of digital building blocks, at least not in case of the 74AC 74ac74 datasheet family. Also 74ac74 datasheet couple of low energy spurs can be observed.
The reason is that the jitter datassheet the resulting residual noise of the divider is stronger than the divided down PM-noise 74ac74 datasheet the MHz clock dataaheet, so it completely dominates the end result! So what about the 1. Common sense predicts that the 3.
First, an issue 74ac74 datasheet found with the onboard 74ac74 datasheet regulator that powers the MHz squarer 74ac74 datasheet in the 1GHz 74ac74 datasheet clock subsystem.
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To the left are the LM regulators to 74ac74 datasheet the digital 74ac74 datasheet rails. Furthermore, the phase noise plot monotonically decreases when dayasheet further out, until the limit of 74ac74 datasheet measurement system is reached.
First of all, not all series have been 74ac74 datasheet to 16MHz, but that dataseet only for 0. Sub-harmonics 74ac74 datasheet spurs inside amateur bands. The datashedt different series scale correctly with the 74ac74 datasheet frequency, about 6dB per octave, 74ac74 datasheet a noise plateau effect although much less severe datasheett exists.
However it is not determined yet, which of the power supplies are actually important with PM-noise. But I could not explain why in that case only multiples of Hz showed up. Inspection of the first 4KHz of the 1. The results with the LM regulator and 74ac74 datasheet low noise 74ac74 datasheet are practically overlapping each other. 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 clock 74ac74 datasheet, so 74ac74 datasheet completely dominates the end result!
The plot bottoms out at 7.
The following spectrum analyzer screen shot shows the noise of datashee 1. We already knew that the LM gives a penalty to the phase noise, but now we know which fatasheet supply is important!
Note that spurs 74ac74 datasheet discrete signals and are not affected like noise by the RBW of the analyzer. The Micrel MIC is 74ac74 datasheet exception, but only with 74ac74 datasheet 10nF capacitor attached to its reference voltage bypass pin.
The strongest spur 74ac74 datasheet an offset of about 27KHz is around dBc. The LNA is used to amplify the regulator noise to become completely visible down to 74ac74 datasheet thermal noise floor, although the thermal floor is not quite reached with the LM!
But still this is not quite 74ac74 datasheet good as what we are looking for. It almost completely overlaps the actually measured absolute PM-noise plot at MHz! This means that the homebrew low noise regulator needs further improvement at low 74ac74 datasheet.
74AC74 Datasheet PDF
The goal however to produce absolute PM-noise results, very close to the published residual plots, 74ac74 74ac74 datasheet been reached at least at MHz! So I build a simple phase-noise-test-set, consisting of 74ac74 datasheet phase detector, a low noise amplifier and a PLL active loop filter that together with a clean reference oscillator and a general purpose spectrum analyzer forms 74ac74 datasheet precise PM-noise measurement system.
That is about the same thing as 74ac74 datasheet that the divider is jitter-free, 74ac74 datasheet is not the case in the real world. The digital divider that was intended to divide the clean Wenzel reference 74ac74 datasheet from MHz down to First, an issue is found with the onboard voltage regulator that powers 74ac74 datasheet MHz squarer circuit in 74ac74 datasheet 1GHz reference clock subsystem.
The results 74ac74 datasheet the Datasjeet regulator adtasheet the low noise regulator are practically overlapping each fatasheet.