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Help with Testing SMD Oscillators

Thread starter #1
I am an electronics student and also work for a small electronics company. I have been given the task of testing 100 SMD CMOS output 10MHz oscillators to see if their resonant frequency holds true at varying temperatures. These are straight from the manufacturer and not on a board. I watched a Youtube video of a guy testing through hole oscillators using a function generator and oscilloscope. That is what I would like to do with these and not have to build a circuit for testing. Is this going to work for me? Any other thoughts or suggestions would be extremely appreciated!

Here is the link to the Youtube video
 
Last edited:

JimB

Super Moderator
Most Helpful Member
#2
I watched a Youtube video
A link to that video would give some insight.

How on earth do you test an oscillator with a function generator?
A frequency counter would be more use than a function generator.

JimB
 

ronsimpson

Well-Known Member
Most Helpful Member
#3
We don't know what is in the youtube.
Are you going to test all 100 parts?
to see if their resonant frequency holds true at varying temperatures.
I would use a frequency counter. Function generators and oscilloscopes are not known for being accurate. Just measure the frequency at several temperatures.
Put the Oscillator in a "hot box" or "cold box" but keep all test equipment at room temperature.

All 100 unites will act the same. Test one and you have almost tested them all.

My guess is that this new oscillator will go into some thing that is made at your location. Go get one of these boards. Measure the part you are now using. (cold/room temp/hot) Replace the oscillator with a new part and repeat the test.
 

JonSea

Well-Known Member
#4
The video is testing plain crystals, not active oscillators. Crystals need to be exicted to oscillate. Your CMOS oscillator contains an excitation source.

All you need to do is apply power and measure output frequency with a counter as you vary temperature.
 

atferrari

Well-Known Member
#5
A link to that video would give some insight.

How on earth do you test an oscillator with a function generator?
A frequency counter would be more use than a function generator.

JimB
Comparing the oscillator's output with the generator's output?
 
Thread starter #6
Thanks for your responses so far. I understand now that the video was for a crystal and mine is a oscillator. It has a six pin surface mount layout and I don't know where to attach probes. I don't have a counter, but my oscilloscope is a nice one. I have a power supply. I have read by some people that you have to put it into an oscillator circuit to test it. I hope that is not correct. I don't have access to a board that it will eventually go back into. They believe that the frequencies in some of these components are changing around 50C. If anyone can give me some details on how I would go about setting it up, I would appreciate it. I plan to use a hotplate with thermocouples to get to the right temperature.
 

JimB

Super Moderator
Most Helpful Member
#7
The linked video is very poor, he does not explain his technique very well (at all?)

I see that you have commented as I am typing, he was testing crystals, you are going to test oscillator modules, there is a big difference.

It has a six pin surface mount layout and I don't know where to attach probes.
Well, you will have to find the datasheet for the oscillator, that will tell you what the connections are.

You will have to connect a power supply to the power pins, and means of measuring the frequency to the output pin.

I don't have a counter, but my oscilloscope is a nice one.
So the oscilloscope is a nice one, so what? How good is it at measuring frequency?
How big a change in frequency do you expect to find in your oscillator?

I think that you really need a frequency counter to accurately measure the frequency.

JimB
 

ronsimpson

Well-Known Member
Most Helpful Member
#8
I think that you really need a frequency counter to accurately measure the frequency.
We don't know what part you have. So I searched for SMT 6 pin 10mhz. The first part to come up is stable over temperature to 1/100,000. Divide up your scope display into 100,000 pieces and think about measuring what fraction of that. Your oscillator is much better than a scope.
 

JonSea

Well-Known Member
#9
How on earth do you test an oscillator with a function generator?


JimB
An oscillator, no, but for a crystal, this is a good way to do it.

A crystal operates at its resonant frequency. To determine what that frquency is, it must be excited. A function generator and an AC voltmeter could do this. Sweep the frequency and look at the frequency where the peak occurs.

Excitation could also be provided by a broadband noise source (white noise) with the response measured with a spectrum analyzer.

For larger structures, a bump test can be used. A short-duration impact provides a broadband excitation. Dropping a crystal a short distance to a solid surface probably would excite the natural (i.e., resonant) frequency, to be measured with a spectrum analyzer. The trick would be ro provide enough shock to have a measurable response without damaging the crystal!
 

JimB

Super Moderator
Most Helpful Member
#10
An oscillator, no, but for a crystal, this is a good way to do it.
I agree, but,
for accurate measurement of crystal frequency, you need an oscillator with very good discrimination, ie very fine frequency resolution.

Here in my "lab" I have three obvious frequency generators:

Hewlett Packard 3312A Function Generator
Hewlett Packard 8640B Signal Generator
Home made DDS based oscillator

The 3312A I would not consider when testing a crystal.
The 8640B would be a reasonable choice for crystal testing, careful adjustment would be needed using the Fine Tune control.
The home made DDS would be my favourite tool for this task. It has 1Hz frequency resolution which would make for easy determination of the crystal resonant frequency.


I have just found this:
www.axtal.com/cms/iwebs/download.aspx?id=91855
It may provide the OP with some insight into oscillator testing.

JimB
 

ronsimpson

Well-Known Member
Most Helpful Member
#12
do I need to build a test circuit or
You are probably going to just solder wires to the pins.
Solder a 0.01uF cap right on the power supply pins. (no wires yet) Then probably add on a 1uF or something larger. Now wires to the supply. Surface mount capacitors!
 

unclejed613

Well-Known Member
#13
For larger structures, a bump test can be used. A short-duration impact provides a broadband excitation. Dropping a crystal a short distance to a solid surface probably would excite the natural (i.e., resonant) frequency, to be measured with a spectrum analyzer. The trick would be ro provide enough shock to have a measurable response without damaging the crystal!
that probably won't work in this case, as there is an oscillator circuit between the crystal and the output terminals.
 

unclejed613

Well-Known Member
#15
it's not too hard to connect a quartz crystal to an amplifier, and have some kind of solenoid whack the circuit board, and see what you get. on the other hand, the mechanical resonance you see may not even be close to the series or parallel resonant frequency of the crystal. there are several different ways of cutting a crystal, and the mechanical and electrical axes can be different. IIRC some of the old crystals in the 1x1.5 inch holders could have their frequency "walked" with a setscrew, or with certain amounts of spring pressure exhibit different oscillation modes. the quartz slab in those was large enough to remove, and lap (grind/polish) to change the operation frequency (you always wanted to start with a crystal below the desired frequency, as removing mass from the crystal increases the resonant frequency).
 

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