Crystal oscillators - Negative resistance and oscillation margin measurements

Рет қаралды 8,656

2 жыл бұрын

#134 In this video I continue looking at quartz crystal oscillator related measurements by taking a closer look at the negative resistance measurement. I look at what this measurement means, and how it can be turned into a more useful parameter which is the oscillation margin. Finally I look at what sort of possibilities there are when you run into problems with the measurement results.
More videos on crystal oscillators:
LTspice Crystal modeling: • Measuring and Simulati...
Oscillation frequency measurement: • Crystal oscillator - F...
Drive level measurement: • Crystal oscillator - D...
Negative resistance measurement: • Crystal oscillators - ...
Links and further reading:
www.maximintegrated.com/en/de...
www.cypress.com/file/88466/do...
www.murata.com/en-global/prod...
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Пікірлер: 34

@acestudioscouk-Ace-G0ACE 2 жыл бұрын

Good information, I need to watch this a few times to get it into my geriatric head.

@wueric4076 2 жыл бұрын

Good demonstration of the temperature dependent gm.

@randydireen3566 2 жыл бұрын

Always love watching your videos. Thanks very much!

@FesZElectronics 2 жыл бұрын

Happy you are enjoying them! Thank you!

@ivanm9674 2 жыл бұрын

Great video! Nice explanation. Thank you!

@felixcat4346 2 жыл бұрын

Another smart one ☺️.

@Nxb9ch 6 ай бұрын

Can you explain the transfer function of a crystal oscillator using mosfet?

@larcomj 2 жыл бұрын

this video was released 27 seconds ago, how lucky am I

@6c45pi 2 жыл бұрын

How can you know if you're lucky until you've watched it?

@stark9397 2 жыл бұрын

Please come transistor, mosfets videos. Which important parameters, how can we choose and how can we control. Sorry my bad english, I hope you understand :)

@SurvivalSquirrel Жыл бұрын

I am searching for an answer, how the voltage of a microcontroller can fluctuate without any problematic effects. Especially with voltageripple and noise/spikes in the range of the maximum values of the microcontroller. I have not found any aspects yet, that would oppose the use of a supply with a voltage ripple of 0.5V, and some noise/spikes. Except, that of course it would affect ADC measurements. I could not find much to this, so i suspect its not problematic?

@babhishek88 2 жыл бұрын

Does the trimming pot add parasitics to the osc_in/out pins?

@FesZElectronics 2 жыл бұрын

It does. The recommended way to do a highly accurate measurement is to first use the trim pot to find the rough value, then use fixed value resistors to fine tune.

@Morganmcc6 2 жыл бұрын

You have to watch out with trim pots when margining crystals. Usually trim pots add a lot of inductance which can non-negligibly affect your margin depending on the crystal

@FesZElectronics 2 жыл бұрын

May I ask what sort of differences did you encounter by using a trim pot as opposed to using fixed value resistors? Just to get an idea of the level of error.

@Morganmcc6 2 жыл бұрын

@@FesZElectronics I've seen as bad as 1.5K being the limit on a pot vs 600 with an 0201 fixed resistor.

@FesZElectronics 2 жыл бұрын

You must have very good eyesight to work with 0201 :D Anyway, I guess this is also frequency dependent - the impact of the extra inductance will be more severe with higher frequency crystals.

@domtom128 2 жыл бұрын

Great video as always! One phenomenon I'm trying to think an explanation of; from 12:27 there seems to be some kind of intermittent frequency mixing of crystal's fundamental and, I presume, its higher harmonic. Same thing was happening in the end with the hot air test (12:01), which is even weirder to me - seems like there is a higher margin for the higher harmonic, or something else?

@FesZElectronics 2 жыл бұрын

I was curious myself why that occurred, but I'm not quite sure yet. I guess it might have something to do with the averaging function used on the oscilloscope - to get eh waveform more static and uniform; but it might also have to do with the current probe and its impedance mismatch (between the probe inductor and the cabling)

@domtom128 2 жыл бұрын

@@FesZElectronics I should've looked more carefully, frequency of those oscillations seems to be ~100 MHz, so my money is on the averaging artifacts since your scope is 70 MHz BW.

@FesZElectronics 2 жыл бұрын

Just because the oscilloscope has a BW of 70, doesn't mean it can't display more than 70M, it will just be attenuated. But I still think its some issue with the oscilloscope :D

@FesZElectronics 2 жыл бұрын

I did some more investigations.. it seems my oscilloscope is on its last leg. I'm getting the oscillation on channel 1 even with the signal generator. Curiously, the oscillation does not appear on channel 2.

@domtom128 2 жыл бұрын

@@FesZElectronics that's interesting. Repair video maybe? :)

@z3d12 2 жыл бұрын

Barkhausen

@LightningHelix101 2 жыл бұрын

That guy really did a 180

@cahitskttaramal3152 5 ай бұрын

why dont you just pıt oscilkoscope probe on the xtal pins?

@FesZElectronics 5 ай бұрын

The probe has 10-20pF of capacitance; adding the prove directly would completely change the oscillators behavior.

@cahitskttaramal3152 5 ай бұрын

@@FesZElectronics What about active probes? They have like 0.2 pF caps at max.

@FesZElectronics 5 ай бұрын

In what I observed from various application notes, measuring the oscillator frequency (the most sensitive test to external factors) should be done indirectly (either near-field probing, or using some other IC pins that output the OSC frequency, when available); but other measurements - like waveform shape or start-up time can be done with an active probe with direct probing.

@cahitskttaramal3152 5 ай бұрын

@@FesZElectronics OK thanks! I am starting to measure my own crystals now :)

@cahitskttaramal3152 5 ай бұрын

@@FesZElectronics Also I didn't catch how did you calculate the already existing 37 ohm ESR of the crystlal? Datasheet only states the maximum.