#132 In this video I continue looking at how quartz crystal oscillator specific measurements can be performed, and today its time for drive level. Since this measurement involved measuring quite a small current, ideally using a small current probe, first task is to make the current probe. Then I proceed to perform some measurements on an oscillator and adjust the components and settings until the drive level requirements are met.
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.infineon.com/dgdl/Infineo...
ww1.microchip.com/downloads/en...
ww1.microchip.com/downloads/en...
www.tme.eu/Document/0e66149b0...
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There are only few KZhead channels concern about basic RF stuff and your channel is best. Thank you for sharing your experience and knowledge.
Bro you are actually the best in what you do. Keep doing it .... 👌👍
this episode is such an eye-opener to me, thanks! I used to just go with the datasheet recommendations with regard to the oscillator current drive adjustment. I now have to make a probe like yours and check my old projects.
I only worked with PICs in the university, I always put HS in the oscillator setting, not understanding at all what means o how it works, only works!, thanks for the video and for the high quality content.
Excellent video :) This makes me wonder if the manufacturing of such cristal did improve over time, explaining why old MCU datasheets suggest a high gain setup for medium-high frequencies. This improvement might also be a reason why few years ago Atmel decided to remove the full swing cristal driver from their AVR chips.
Fantastic video! Enjoyed every minute. Especially like your skilfully built current probe! Now I want one.
Thanks for the very informative video.Oscillator startup is a good test to do. Taking the drive level too low may make the wake-up from sleep too long. Another set of tests to do is start-up at high and low temperatures 🙂
Of course! I covered that also in a later video. With oscillator tests, all of them need to be done, and all of them need to give good results. I would maybe also add, that other than temperature, supply voltage is also important to consider. Worst case needs to take into account not just temperature conditions, but also supply conditions.
@@FesZElectronics That is a very good point! Thank you
Great and comprehensive video , Obviously a lot of work have been done to produce this video.
Excellent explanation. You've again made great video.
Again i learned from you! Thx
Very nice! Concise & precise.
Excelent eplanation, thank you very much for this video!
very well made explanation !
The transistor pendulum cracked me up. Reminded me of uni days.
Very good video thanks for posting
Very interesting video. Good to see some RF stuff. Could you upload some info on choosing the values of the feedback capacitors in a simple common emitter xtal oscillator. It seems most designs use two similar value capacitors and the circuit works. But what are the trade offs?
You're the man
Nice video, thanks :)
What is the Pk to Pk voltage of the clock signal when measured on the PCB? and how do we measure a clock signal on crystal output because when I put an oscilloscope probe on CL(load capacitor) that will change CL capacitance to the crystal and alter the frequency?
Very useful. R is similar to inverse 2 pi frequency capacitance.
Any video on explaining working of transmitters and receiver module circuit diagram
Good explanation of Xtal drive level measurement. For those low frequency XTAL like RTC 32.768 KHz, I don't think this method work. RTC Xtal's ESR is very high like 50 Kohm that the current flowing is far too low to measure. Do you have another method to measure it?
Is it possible to make a video for driving high power ( like 40 - 60w) ultrasonic transducer?
thank you
Fascinating video, so informative - thanks. For those who do not want to build the current probe, would it be adequate to use a variable resistor from the Oscillator output to the crystal and trim it for best sin wave, maybe even using the scopes FFT to trim for minimum harmonics? Then replace the variable with an equivalent fixed resistor?
Not necessarily; just because you are seeing a sine wave, it doesn't mean that the drive level is in check - you can have very nice looking waveforms and still exceed the drive level
The resonance and response above 90 MHz is likely due to the long thin wire through your current transformer. I suspect if you shrank the wire loop so the 50 Ohm load was much closer to the point where you break the coax, the high end of your measured flat response would go up.
I think you are right, there is an impedance mismatch between the coax cabling and the probe wires. I will try to re-measure the response of the probe once I get some trim pots (I am planning to order some tiny ones that can fit inside of the case); I want to put a trim pot in parallel with the BNC on the probe side to reduce the response to a 5mV/mA - I don't expect this to completely fix the response above 90M just to slightly improve on it; or maybe put the trim pot in series, to facilitate a less sharp impedance transition...
@@FesZElectronics The size of the current loop matters on both sides; I was primarliy talking about the loop you set up to measure with your probe. It should be reduced a lot. Look at the test fixture Joe Smith set up to work on his Tektronix current probe.
@@Chris_Grossman I guess you are referring to this thing: kzhead.info/sun/acpxqtOxeaqfras/bejne.html ; I honestly did not consider the impact of the "input" coil, thanks for the hint!
@@FesZElectronics Correct!
Thank you, that was very useful. I was just thinking of making a current probe for 1-30 MHz frequency range to properly measure the efficiency of the class C RF power amplifier! 🙏
I guess it won't be that difficult to make the probe, but if you are measuring high currents, it might be useful to verify that the measurement is still accurate as current increases - core saturation will cause a decrease in permeability at some point
@@FesZElectronics So I made a probe using 10 turns of 0.9mm copper wire on Amidon FT50-43 core. The response turned out to be VERY flat in a 100 kHz-150 Mhz range, and it gives ~4.75 mV/mA when loaded to 50 Ohms.
Its quite nice that you got so close to the 5mV/mA that you should be getting with 10 turns; I really wonder why I only got 6.8 mV/mA with 5 turns... I think I tried it out up to ~20MHz but a similar ratio was present.
If you end up doing that, please post a video. I have been wanting to do this to view current waveforms in a class E RF power amplifier for tuning purposes.
Great video as always, but I have 2 things: 1. Why did you reduce the Urms voltage measuring range in 19:34? The general rule is to make measurements as close to the measuring range of the instrument as possible. Before switching I noticed that the Urms_cyclic voltage (because this is what we are interested in) was equal to 9.0V, not 9.6V. As a result, the measurement error is about 7%. 2, Could you please maximize all the drawings so that they fill the whole screen as much as possible? Sometimes I watch YT movies on my smartphone, and then some details are difficult to read.
I liked the current probe design you made. Did you use the core impedance graph to come up with 1 turn and for 5 turns? Curious to see the math thanks
Not really; the "1 turn" refers to the measured wire - you want this wire to pass trough the core only once - so 1 turn; the 5 turns will first of all set the currents ratio between primary and secondary, but also based on the secondary inductance, you will set the minimum frequency that can be measured - so you want many turns to measure low frequencies but want few turns to see a large measured voltage; the compromise I took was 5 turns
Hi Fesz, thank you for this very helpful video. I also recently made a current transformer to detect common mode interference currents on power lines. I used 3E6 material ferrite ring from Ferroxcube which has a very high permeability ui=10000. Since the high frequency limit is mainly determined by the burden resistor and the parasitic capacitance between the secondary windings. My secondary windings is 10 turns, and the parasitic capacitance I estimate should be around 10pF, so the high frequency limit should be very high. But after the test, I found that the high frequency limit is only about 10MHz. After reading the technical manual of 3E6 material, I found that its permeability starts to drop significantly after 300kHz, do you think this is the reason why the high frequency limit is suppressed?
With most ferrites, the permeability doesn't just drop at high frequency, the material also becomes absorbent; At "low" frequency you will have real permeability - the coil will work like an inductor, store and release the magnetic field; but at high frequency, you get imaginary permeability, the coil will work like a resistor - the magnetic field will be turned to heat; this is the principle on which ferrite beads work.
@@FesZElectronics Hi FesZ. Thanks a lot for your reply, it seems that choosing the right ferrite material is not that simple. I chose high permeability materials because they are more responsive to magnetic fields, which can keep up with small phase errors. But I found that high permeability materials tend to have smaller bandwidths and greater also big imaginary permeability. I found K1 material from TDK with a real permeability of ui=80 and constant until 20MHz, and a low imaginary permeability. Do you think this is a more suitable material?
at 17:42, why do you use the peak to peak value directly as V_rms? Don't you have to divide by 2*sqrt(2)?
I think this is a misunderstanding; the oscilloscope is printing 4.4mV as Vrms and 13.0 as Vpp; it is true the cursor is left on Vpp, but the rms value is used in the calculation.
Ah my bad, thanks!
Are you measuring peak to peak or RMS? Looks to me you are measuring peak to peak voltage so a 1/2sqrt(2) is missing in the equation no?
I was using the RMS that the oscilloscope was calculating
There is another way, by measuring the voltage saing at the amplifier input, with a 1 pF active probe
Great video. Why not use wideband surface mount ferrite transformers like those made by Minicircuits or Macom? They are small enough that you could make something super compact with surface mount parts.
FWIW, I only ask because I couldn't find those Richco beads on the usual sites here in the US.
Subscribed :)
Any core should work as long as the datasheet specifies that its usable up to the frequency of interest - I am by no way saying that the cores I used are the only ones; my method for choosing them was that they had to be in stock and smaller than 9mm diameter, and have some impedance curves :D
@@FesZElectronics Thanks. Finding stuff that is in stock is even more important in the crazy times.
2:10 too hipnotyc , I'already sleep :DDD 100 Like :D
Now I want to seriously talk to you why you didn't get the 10 mV / mA gain. There is only one thing to clarify. Did you really directly connect the secondary of the transformer to the 50 Ohm input of the oscilloscope with a cable with the same characteristic impedance? What cable was used and how long was it? I'm asking this to get down to quantitative estimates.
Hello! I had a 2.2nF in parallel with a 470R, all in series with the secondary and cable; the cable was ~ 55cm 50R cable; the oscilloscope doesn't have a 50R internal termination so I added it externally. I guess the issue might be with the magnetic core - it might have a bit more losses that expected at this frequency...
@@FesZElectronics I was hoping to find out the type of cable like RJ58 or something. First of all, I am interested in the linear capacity of the cable. Indeed, at a frequency of 8 MHz, the wavelength is much, much more than 55 cm, and therefore this piece is correctly considered as a set of lumped elements, and not as a distributed transmission line. Then we will take a few steps with you to build an equivalent circuit of the input impedance of your sensor and its gain, taking into account parasitic values. And then, if you wish, consider the higher frequencies. So, now you can just measure capacitance of cable.
@@FesZElectronics If you now want to disassemble this problem without my help, then pay attention to the even larger dimensions of the primary coil and one of the secondary turns. Their influence can also be very strong. Good luck!
I don't mean any disrespect, I just don't always have time, or just forget to reply... The cable is RG174; Honestly I suspect some measurement issues with the oscilloscope, it started to show signs of various errors, and that is why I don't really want to focus on this measurement result at the moment. I plan to do a dedicated video on this sort of passive current probes where I want to re-analyze these measurements and how these probes work. Regarding the primary turn, this was also pointed out by another viewer, so I plan to try to make a dedicated setup to perform the calibration measurements.
@@FesZElectronics Don't bother. I wish you good luck in a positive way. I, too, can be busy and forgetful. Let's keep this in mind and humble ourselves. I will try one of these days to write my thoughts on the replacement scheme in more detail.
Please check the subtitles. They are in Vietnamese.
No idea why that happened... the video was clearly labeled as having the audio in English. Ah yes, this is the AI that will take over the world :D
@@FesZElectronics ;)
@@FesZElectronics Please try to enable subtitles again. I miss them.
Please, can you explain in arabic?? 🙏🙏🙏🙏🙏Pliz
Helo....mr
این بابا هم شده یه تکس بوک دیگه .از روی کتاب میگه .اخه آدم حسابی کسی که میاد تو اینترنت دنبال الکترونیک یه ادم عاشق الکترونیک است .مرد حسابی یک مداری... نمونه ای... مثالی عملی .. یه چیزی که جالب و جذاب باشه اینطوری یه مطلب کلاسیک علمی را هم میشه خوب شیر فهم شد ..نه اینطور یکسره زر میزنه.. خوابم گرفت حیف نت.