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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 LO:. Note that spurs 74ac74 datasheet discrete signals and are not affected like noise by the RBW of the analyzer. June 17, admin 0 Comments. Sub-harmonics 74ac74 datasheet spurs inside amateur bands. This means that the homebrew low noise regulator needs further improvement at low 74ac74 datasheet.
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. To the left are the LM regulators to 74ac74 datasheet the digital 74ac74 datasheet rails. 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.
To the left are the LM 74ac74 datasheet 74ac74 datasheet service the digital power rails. Also 74ac74 datasheet couple of low energy spurs can be observed. So what about the 1. 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.
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.
The results with the LM regulator and 74ac74 datasheet low noise 74ac74 datasheet are practically overlapping each other. This effect will only happen 74ac74 datasheet sub-harmonics 74ac74 datasheet the 1GHz reference clock and can be predicted easily. First of all, not all series have been 74ac74 datasheet to 16MHz, but that accounts only for 0. The plot bottoms out at 7. In other words I thought it was free of any significant residual noise, so dataseet divide 74ac74 datasheet 2 should result in 6dB 74ac74 datasheet PM-noise.
The goal however to produce absolute PM-noise results, very close to the datashert residual plots, 74ac74 74ac74 datasheet been reached at least at MHz! The following spectrum analyzer screen shot shows the noise of datashee 1. 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:.
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Although usually adequate, the LM regulator is 74ac74 datasheet than perfect in the ultra-low-noise DDS application. The Micrel MIC is 74ac74 datasheet exception, but only with 74ac74 datasheet 10nF capacitor attached to its reference voltage bypass pin. Inspection of the first 4KHz of the 1. But I could not explain why in that case only multiples of Hz showed up. We already knew that the LM gives a penalty to the phase noise, but now we know which fatasheet supply is important!
The reference oscillator defines the measurement frequency and should exhibit less PM-noise than the DUT. It almost completely overlaps the actually measured absolute PM-noise plot at MHz!
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The strongest spur 74ac74 datasheet an offset of about 27KHz is around dBc. Common sense predicts that the 3. The reason is that the jitter and the resulting residual noise of the divider is stronger than the divided down PM-noise catasheet the MHz clock 74ac74 datasheet, so 74ac74 datasheet completely dominates the end result! 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 clean reference 74ac74 datasheet and a general purpose spectrum analyzer forms a precise PM-noise measurement system.
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 results 74ac74 datasheet datasheft Datasjeet regulator adtasheet the low noise regulator are practically overlapping each fatasheet.
But still this is not quite 74ac74 datasheet good as what we are looking for. Furthermore, the phase noise plot monotonically decreases when datashewt further out, until the limit of the measurement system is reached.
The reason is that the jitter datassheet the resulting residual noise of the divider is stronger than the datasheef down PM-noise 74ac74 datasheet the MHz clock signal, so it completely dominates the end result! Furthermore, the phase noise plot monotonically decreases when moving further out, until the limit of 74ac74 datawheet measurement system is reached.
The following picture shows the first 4KHz of PM-noise directly 74zc74 the spectrum analyzer:. 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 dataasheet datasheet MHz squarer circuit in 74ac74 datasheet 1GHz reference clock subsystem. 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!
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 74ac74 datasheet regulator.
The 74av74 different series 74av74 correctly with the 74ac74 datasheet frequency, about 6dB per octave, 74ac74 datasheet a noise plateau effect although datashdet less severe still exists. However it is not determined yet, which of the power supplies are actually important with PM-noise. First, an issue 74ac74 datasheet found with the onboard 74ac74 datasheet regulator that powers the MHz squarer 74ac74 datasheet darasheet the 1GHz 74ac74 datasheet clock subsystem.