Quickly, accurately, repeatably measuring xtal/osc frequency - Page 1
Forum section: electronics / beginners

author: whatever
author_rank: Contributor
timestamp: January 08, 2024, 05:33:57 am
content: Say I have to measure several dozen 2-pin xtal cans, 4.00 Mhz to 80.00 Mhz. They need to be checked for accuracy. All are hot-swappable in a 5v based DIY driver ckt. (see photo). This works very well.But where I run into weird issues is when the same xtal is in the ckt they are intended to be used. Say an audio D/A, DVD player or CD player. Measurementin situ, with xtal across an IC's X_in to X_out "driver pins" gives all sorts of distorted or inaccurate readings; perhaps, only the old Tek 465 is most reliable and repeatable for xtals in circuit.What I have to measure:I have an old-school but calibrated Tek 465, a modern Siglent 1202x-e dso, NanoVNA, NanaoSA, Owon xdm2041 desktop dmm, and Koolertron DDS sig gen/counter.Does anyone have preferences?==================Test jig:Works well even with simple DDS counter:But here's where I run into issues (e.g., measuring in circuit, with xtal driven by microprocessor's X_in/X_out pins. I get no or garbage readings when probing at X_in or X_out -- with dso, dds, dmm, NanoSA, etc):[/url

author: Andy Chee
author_rank: Super Contributor
timestamp: January 08, 2024, 05:59:48 am
content: When measuring crystal oscillator circuits in situ, it's extremely easy to disrupt its operation merely by the stray capacitance from directly connecting your probe.In other words, do not directly connect your probe to the Xtal oscillator, use a small antenna loop (use Dave's trick of connecting the probe alligator back to the probe tip).

author: MathWizard
author_rank: Super Contributor
timestamp: January 08, 2024, 07:29:36 am
content: So do you mean connect probe GND to probe tip to form a 1 loop inductor, and put it near some oscillator and you will see a little blip on your scope ?I'm probably mixing that up

author: Andy Chee
author_rank: Super Contributor
timestamp: January 08, 2024, 07:50:15 am
content: Quote from: MathWizard on January 08, 2024, 07:29:36 amPretty much! Should even be enough length in the ground lead to form a small diameter pickup loop.Of course, it won't give you any calibrated voltage reading, but it should be enough to sense the operating frequency of a xtal oscillator.

author: David Hess
author_rank: Super Contributor
timestamp: January 08, 2024, 08:08:46 am
content: You should be able to measure the frequency by probing the output of the gate oscillator, but the probe loading still needs to be small, so use a x10 oscilloscope probe.Get a frequency counter which has a 1 megohm high impedance input like an oscilloscope does, and use a x10 oscilloscope probe with it. Universal counters usually have these inputs and work up to 100 MHz. Something like an HP 5314A, HP 5315A, or HP 5316A would be ideal.Even better, use a low capacitance active probe. If they are too expensive, then you can make one as shown below.

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: January 08, 2024, 11:42:02 am
content: "Say I have to measure several dozen 2-pin xtal cans, 4.00 Mhz to 80.00 Mhz. They need to be checked for accuracy"Are you sure? If you are using crystals as basic clock oscillators in equipment the exact frequency doesn't matter. Few of these circuits include a trimmer to set the frequency. Crystals can be "pulled" by up to around 5 KHz by components used in the oscillator circuit.Old crystals are likely to be slightly off frequency due to ageing. They also might not pull onto frequency. But unless you are using them in filters, transmitters, or frequency counters, just check if they oscillate or not. Even sluggish crystals generally oscillate if the circuit is driving them hard enough.SJ

author: whatever
author_rank: Contributor
timestamp: January 08, 2024, 01:39:27 pm
content: Quote from: David Hess on January 08, 2024, 08:08:46 amJust curious: What book is that Figure 2.3 from?I was wondering if the solution is not as simple as what is shown in Fig. 2. of this document:https://pdfserv.maximintegrated.com/en/an/AN4949.pdf

author: CaptDon
author_rank: Super Contributor
timestamp: January 08, 2024, 02:02:25 pm
content: It is indeed very true that many L.S.I. integrated circuits have very feeble and easily disturbed Xtal as well as R/C and L/C oscillator circuits. Often these circuits have a CLK output at some divisor of the Xtal frequency and that is where you measure and then multiply the reading if need be. One of the circuits I tested in a QC/QA environment years ago could not be touched by any probe at all. There was a trimmer to set the oscillator at 1MHz exactly + or - 5Hz max. I set a little Sony transistor radio on top of the unit under test tuned to 1MHz and placed some leakage from a very precise 1MHz oscillator nearby. The radio picked up the beat frequency between the two oscillators and allowed me to trim the U.U.T. without probing it. Our best low capacitance probe 'pulled' the oscillator nearly 10KHz. If the circuit was of by 5Hz it could gain or lose about 1 minute in 138 days but I could trim it to within better than 2Hz gaining or losing about 1 minute in a year. It was part of a test instrument which generated tones and had a real time clock for logging. They made wasteful use of the 1MHz oscillator for the R.T.C. as opposed to a simple 32.768KHz arrangement but it was all CMOS so it was still not too harsh on the backup battery.

author: radiolistener
author_rank: Super Contributor
timestamp: January 08, 2024, 03:09:46 pm
content: I think the most easy way is to use some cheap frequency meter from aliexpress and SDR receiver for calibration, you can calibrate your frequency meter with according to standard frequency and time signal radio station available in your region using SDR receiver. Then just put your crystal into simple generator circuit and measure it's frequency with frequency meter...You can use something like this:https://www.aliexpress.com/item/1005006321816803.htmlThere is also crystal oscillator frequency meter diy kit:https://www.aliexpress.com/item/32847750953.htmlit has less precision, but allows jut to put your oscillator into device and see it's frequency on the display...

author: David Hess
author_rank: Super Contributor
timestamp: January 08, 2024, 03:58:52 pm
content: Quote from: whatever on January 08, 2024, 01:39:27 pmTroubleshooting Analog Circuits by Robert Pease.QuoteI have made the measurement in exactly that way, although without the 200k resistance. It usually works but as pointed out, may pull the crystal frequency. In some cases the probe's input capacitance can replace the associated capacitor to ground, or be compensated for.As CaptDon points out, there may be another spot to probe the divided frequency which will not affect the crystal oscillator.

author: whatever
author_rank: Contributor
timestamp: January 08, 2024, 07:13:49 pm
content: Yes, probing the X_o / X_in pins of an active device (CD player playing) can cause issues; but those issues are not repeatable.Below are various diy osc (clock) projects for audiophile experiments. These clocks almost always behave and do not have aforementioned probing issues while in active (in circuit) use. To replace the OEM xtal with new clock, one simply removes the orig xtal and its caps. Then, the outboard clock is connected to processor (IC) X_in pin; the X_out pin is not used and remains open.

author: selcuk
author_rank: Frequent Contributor
timestamp: January 08, 2024, 09:24:20 pm
content: This is a two-page quick reference about crystal load capacitance. Please check the warning and recommendation about oscilloscope probe on the second page.https://www.raltron.com/webproducts/technical/technical_notes/RT-DWG-LoadCapConsiderations-1a-final.pdf

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: January 09, 2024, 12:59:28 am
content: Capt Don's idea is really cool. And it works.Your reading of the freq will be only as accurate as the time base of the instrument you are using. Here is a quick way of getting a decent reading.Use the most accurate instrument you have,Put a 10X probe on your Spectrum and put it near the xtal with the ground lead shorted to the tip (Dave's Trick, used by many radio tecks for many years.)Spectrum is more sensitive than the scope almost all the time.For quick checks sometimes I just put the Scope/Spectrum Analyzer probe on the Xtal Case. This works but can disturb the Xtal.The inputs n a SA will "load" down the circuit more than scope probes if you attach them to the circuit because they are typically 50 ohm inputs rather that thousands of ohms, but they are more sensitive.As stated "attaching" anything to the osc circuit will probably change the behavior of the xtal even stopping it .There may be a pin on the nearby IC that serves as a "buffer" for the generated xtal freq and would be a good place to actually see the signal. Putting a lead on the Xtal in and out would probably stop the oscillation, since that connects directly to the xtal. Perhaps probe the other leads or find the freq out (clock out) lead of the IC. That way you are sampling a signal not from the oscillator itself but from an amplifier of that signal.

author: whatever
author_rank: Contributor
timestamp: January 09, 2024, 02:45:09 am
content: Useful feedback to all! Thx!Yeah, putting a probe on the xtal pins-- even if those pins have a loaded connection to IC's X_in and X_out driver pins --is likely the culprit. And why the BCK signal is almost never affected. For CDPs, it's usually a 1.44 Mhz As shown here on my Tek 465:One of the reasons why audiophile designers like to opt for external clocks - - with a clean, dedicated pwr source of their own -- is so the DAC or digital filter ASICs don't have to multi-task.

author: whatever
author_rank: Contributor
timestamp: January 09, 2024, 08:04:29 am
content: One more thing that I should note is that neat little sn74lvc1gx04 shown above,After tweaking the DS-suggested schematic a little, one gets some very clean waveforms out of this tiny device. It's 'scope performance rivals that of many "audiophile super-clocks". At 5.0 volts, the sn74lvc1gx04 osc. draws about 20mA. That is not an insignificant current draw. So I can see some advantage in feeding such a clean clock signal into the DAC's X_in pin; hence, taking some pressure off the DAC's internal pwr ckt.EDIT: Is the mc12060/61 a better xtal driver?

author: radiolistener
author_rank: Super Contributor
timestamp: January 11, 2024, 12:02:35 am
content: Quote from: whatever on January 09, 2024, 02:45:09 amThe reason is that DAC SNR depends on it's clock jitter/phase noise and ultra low phase noise oscillator is more expensive. So, they can put more cheap oscillator for economy and option to allow use external oscillator for those who want better dynamic range.

author: whatever
author_rank: Contributor
timestamp: January 11, 2024, 03:07:13 am
content: Quote from: radiolistener on January 11, 2024, 12:02:35 amWell, theoretically, the XO's that are driven by the ASIC should have the cleanest, shortest path to the circuitsinthe ASIC that need the XO clock timer.I consider myself an audiophool. I can (subjectively) hear the diff. a good, external clock can make. However, when it comes to measurements, I do them. And the simple clocks come up looking as clean as the overbuilt ones. Case in point, the sn74vc1gxo4 driver project I built (see photo).

author: radiolistener
author_rank: Super Contributor
timestamp: January 11, 2024, 03:40:33 am
content: Quote from: whatever on January 11, 2024, 03:07:13 amI don't know about ASIC chips, but FPGA chips have very high phase noise and cannot be used as a low phase noise clock source for high dynamic range ADC/DAC. Usually ADC/DAC is clocked from low phase noise clock source directly, and ASIC/FPGA process the data clocked from the same source through buffer which goal is to isolate clock source from noisy FPGA/ASIC chip.

author: Kim Christensen
author_rank: Super Contributor
timestamp: January 11, 2024, 04:56:50 am
content: Quote from: whatever on January 08, 2024, 07:13:49 pmThe reason for this is because the thing in the can is not just a crystal. It's a TCXO (Temperature compensated crystal oscillator) so you're not probing a crystal at all, but rather the buffered output of an oscillator.

author: tggzzz
author_rank: Super Contributor
timestamp: January 11, 2024, 06:15:51 am
content: Quote from: whatever on May 28, 1975, 01:55:22 amThat is not a crystal.That is a crystal plus amplifier plus passive components plus buffer all contained within a shielded can.The passives will include PSU noise suppression. The buffer will isolate the crystal oscillator from external circuits/probes and external noise on the output.

author: Andy Chee
author_rank: Super Contributor
timestamp: January 11, 2024, 06:34:21 am
content: For reference, Dave also perfomed a teardown of these things

author: whatever
author_rank: Contributor
timestamp: January 12, 2024, 07:57:27 am
content: BTW ... does anyone have info on how well crystal oscillators tolerate soldering heat?Seems as if that wafer is in a precise position (gap) ... does it distort with heat? so maybe clipping an alligator heat sink may not be a bad idea? Yes? No?

author: tggzzz
author_rank: Super Contributor
timestamp: January 12, 2024, 09:37:34 am
content: Quote from: whatever on January 12, 2024, 07:57:27 amYes, the manufacturers do.They helpfully put the information in their datasheets, often in the form of a soldering temperature-vs-time graph.QuoteWhat wafer, what gap?The force exerted by clipping and suspending the clamp in the air may cause distortion. Or not.Quantifythe effects that you think are important to you, and why they are important. Don't use adjectives.

author: Andy Chee
author_rank: Super Contributor
timestamp: January 12, 2024, 10:04:00 am
content: Quote from: whatever on January 12, 2024, 07:57:27 amNo. The crystal frequency is determined by its thickness, not the position of its mounting attachments.

author: whatever
author_rank: Contributor
timestamp: January 12, 2024, 11:02:56 am
content: Quote from: Andy Chee on January 12, 2024, 10:04:00 amWhat does have to do with soldering heat, heat damage/distortion, and temp.effects?Also: from Wikipedia:https://en.wikipedia.org/wiki/Crystal_oscillator" Crystal is the common term used in electronics for the frequency-determining component, a wafer of quartz crystal or ceramic with electrodes connected to it.""The gap between the electrodes and the resonator act as two small series capacitors, making the crystal less sensitive to circuit influences.

author: Andy Chee
author_rank: Super Contributor
timestamp: January 12, 2024, 11:25:25 am
content: Quote from: whatever on January 12, 2024, 11:02:56 amIt tells you that the soldering heat, heat damage/distortion, and temperature effects, must directly affect the crystal wafer to affect frequency.The physical mounting attachments is not a precision mounting. It is the thickness of the wafer that is precisely cut and it's the thickness that determines frequency.

author: shapirus
author_rank: Super Contributor
timestamp: January 12, 2024, 11:38:10 am
content: Quote from: whatever on January 08, 2024, 05:33:57 amPlease share schematics, if it's not a secret. I need to build one too.

author: tggzzz
author_rank: Super Contributor
timestamp: January 12, 2024, 11:41:12 am
content: Quote from: Andy Chee on January 12, 2024, 11:25:25 amThe OP has has described himself in a way that helps understand his responses (myemphasis) ....Quote from: whatever on January 11, 2024, 03:07:13 amThat "clean" clock photo shows a waveform with decent signal integrity on his Tek465. And that'sallit shows.

author: vk6zgo
author_rank: Super Contributor
timestamp: January 12, 2024, 02:30:38 pm
content: Quote from: whatever on January 08, 2024, 05:33:57 amWhen using the 465 do you use the "CH1 vert sig out" to feed your frequency counter?Before my 7613 failed, I found that very convenient with my less than stellar frequency counter, as it provided a controllable gain buffer with built in waveform display----you can't get much better than that!In most of the crystal oscillator stages I've looked at, I have just placed the 'scope probe in close proximity to the metal body of the crystal package.There is usually enough pickup, but if it is a bit minimal, I rest the outside of the "witch's hat against the body.As there is no real direct connection, I often used "x1"probes.

author: whatever
author_rank: Contributor
timestamp: January 12, 2024, 03:49:43 pm
content: Quote from: shapirus on January 12, 2024, 11:38:10 amI encourage you to build the Kwack Clock first. Shown in my images.That said, the easier option is:Use the schematic in the hsn74vc1gxo4 datasheet.https://www.ti.com/lit/ds/symlink/sn74lvc1g04.pdfYou'll need a PCB to solder that 6-pinner SOT to. Ali has them.Add a high-quality 220uF electro cap across the Vcc and GND. Add a ferrite in series with Vcc. Add a high quality R (say 50 ohm) on the signal (out) pin. Use a typical socket (female) connector for 2-pin xtal plug-in. You can use a variable PSU, as shown in my images, to see what effects voltage and current have on the waveform. That PSU also allows one to monitor current drawn at various voltages.BTW: the sn74lvc1g04 and mc12060/61 are limited to a max of 28Mhz. There are xtals cut to much higher primary (fundamental) tones than 28mHz. If anyone knows of standalone osc. driver capable of driving. higher Mhz, let us know.

author: Andy Chee
author_rank: Super Contributor
timestamp: January 12, 2024, 03:54:27 pm
content: Quote from: whatever on January 12, 2024, 03:49:43 pmHow about 200MHz?https://www.digikey.com.au/en/products/detail/crystek-corporation/CCO-083-200-000/1643961

author: whatever
author_rank: Contributor
timestamp: January 12, 2024, 04:02:45 pm
content: Quote from: Andy Chee on January 12, 2024, 03:54:27 pmHuh?That ain't no standalone osc.driver.

author: Andy Chee
author_rank: Super Contributor
timestamp: January 12, 2024, 04:09:04 pm
content: Quote from: whatever on January 12, 2024, 04:02:45 pmThe driver is inside the can with the crystal.

author: shapirus
author_rank: Super Contributor
timestamp: January 12, 2024, 04:39:13 pm
content: Quote from: whatever on January 12, 2024, 03:49:43 pmWell there's no oscillator circuit in that datasheet, but as far as I understand, and from what I can see in your photos, it appears to be the classic Pierce oscillator (https://en.wikipedia.org/wiki/Pierce_oscillator).The PCB, VCC decoupling and output resistors are all trivial things, but what I'm curious about, if it's indeed the Pierce oscillator, is what values did you use for the feedback resistor and for the two load capacitors to make this work well over a wide range of the crystals' resonanant frequencies.

author: Kim Christensen
author_rank: Super Contributor
timestamp: January 12, 2024, 04:44:36 pm
content: Quote from: whatever on January 12, 2024, 04:02:45 pmLook at the datasheet.Here's one that's similarNotice the name "High Frequency SineWave Crystal Oscillator", and the fact that they spec power supply voltage and current draw among other things. There's an oscillator and buffer amplifier, inside that can, in addition to the crystal.

author: whatever
author_rank: Contributor
timestamp: January 12, 2024, 06:42:05 pm
content: Quote from: shapirus on January 12, 2024, 04:39:13 pmYou're right.My bad!!Those TI part numbers are so similar.SN74LVC1GX04 Crystal Oscillator DriverHere you go:https://www.ti.com/lit/ds/symlink/sn74lvc1gx04.pdf

author: whatever
author_rank: Contributor
timestamp: January 12, 2024, 06:49:56 pm
content: Quote from: Kim Christensen on January 12, 2024, 04:44:36 pmAgain, this is not a driver!What some could have suggested was what Dave dug up in that video.It is that NPC driver[https://pdf1.alldatasheet.com/datasheet-pdf/view/7681/NPC/613N1.htmlthat is inside the one of those 4-pin oscillator cans.https://youtu.be/dkdLWronrlk?t=364https://youtu.be/fZYtdE2AF6g

author: Andy Chee
author_rank: Super Contributor
timestamp: January 12, 2024, 07:00:34 pm
content: Quote from: whatever on January 12, 2024, 06:49:56 pmWhat's wrong with the 613N1? According to the datasheet it operates up to 50MHz. And the 200MHz crystal oscillator will have a faster driver again.

author: Kim Christensen
author_rank: Super Contributor
timestamp: January 12, 2024, 07:26:20 pm
content: Quote from: whatever on January 12, 2024, 06:49:56 pmI think you are confused. Buffer... Driver... Whatever. Generally it's an amplifier that follows the oscillator which prevents the load from effecting the oscillator. Either a buffer or driver will work. A buffer is usually an amplifier with a gain of one and a driver is an amplifier with a gain greater than one. Both are amplifiers stages. Maybe I'm confused by what you're after or are trying to say.Nowhere on the NPC SM5613 datasheet is the word "driver" mentioned. They use the term "output buffer" and the only thing mentioned is TTL/CMOSdrivability...