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Crystal Oscillator problem

M

Mig

Jan 1, 1970
0
I encountered with very strange problem with a ceramic crystal
oscillator.
It took a long time to recreate the problem.
When a power supply voltage is turned on first time there is no output
frequency. When the power supply is turned off and on again the
frequency appears.
You can see it on the video here.
Any suggestions?
The vendor doesn't know why it happens. :(
 
D

Don Bowey

Jan 1, 1970
0
I encountered with very strange problem with a ceramic crystal
oscillator.
It took a long time to recreate the problem.
When a power supply voltage is turned on first time there is no output
frequency. When the power supply is turned off and on again the
frequency appears.
You can see it on the video here.
Any suggestions?
The vendor doesn't know why it happens. :(

Post the schematic somewhere. Too little gain or feedback.
 
S

Spehro Pefhany

Jan 1, 1970
0
I encountered with very strange problem with a ceramic crystal
oscillator.

Ceramic or crystal? They're different animals.
It took a long time to recreate the problem.
When a power supply voltage is turned on first time there is no output
frequency. When the power supply is turned off and on again the
frequency appears.
You can see it on the video here.
Any suggestions?
The vendor doesn't know why it happens. :(

It could be an analog problem with the start-up (eg. load capacitors
wrong or not enough gain, or biasing not present) or it could be
something else entirely like your circuit (if it's some complex chip)
going into sleep mode or whatever. Best show us the complete circuit--
and don't expect oscillators built on plug breadboards (if that's
what you have) to work reliably.


Best regards,
Spehro Pefhany
 
M

Mig

Jan 1, 1970
0
Ceramic or crystal? They're different animals.


It could be an analog problem with the start-up (eg. load capacitors
wrong or not enough gain, or biasing not present) or it could be
something else entirely like your circuit (if it's some complex chip)
going into sleep mode or whatever. Best show us the complete circuit--
and don't expect oscillators built on plug breadboards (if that's
what you have) to work reliably.

Best regards,
Spehro Pefhany

Sorry my mistake. This is no a crystal. It is a ceramic.
There is no schematic.
The part comes with 4 pins, Power, GND, Enable and Frequency output.
I'm just testing the bad part that malfunctioned on the board.
I connected just a power and hooked the oscilloscope to the output.
That the first time ever I have encountered with the problem with the
ceramic oscillator!
 
T

Tim Shoppa

Jan 1, 1970
0
I encountered with very strange problem with a ceramic crystal
oscillator.
It took a long time to recreate the problem.
When a power supply voltage is turned on first time there is no output
frequency. When the power supply is turned off and on again the
frequency appears.
You can see it on the video here.
Any suggestions?
The vendor doesn't know why it happens. :(

Desiging an oscillator that will start up reliably 100 percent of the
time is far more difficult than designing an oscillator that works
most of the time.

This is a pre-canned oscillator, right? Or wrong?

Most of the pre-canned oscillators are pretty good. But look carefully
at the output load capacitance specs. If this is a canned oscillator
designed to put out a digital train, and it's putting out a sine wave
(what I see on the scope!), you must have a lot of capacitive load on
the output.

If it's not a canned oscillator, it looks like your oscillator is not
going into deep saturation after startup (that looks like a sine wave
on the scope), so more gain would help with startup. (Not necessarily
reliable startup! You will find with too much gain that you start mode-
hopping or stick to some mode you didn't want to excite.)

Tim.
 
J

Jamie

Jan 1, 1970
0
Mig said:
Sorry my mistake. This is no a crystal. It is a ceramic.
There is no schematic.
The part comes with 4 pins, Power, GND, Enable and Frequency output.
I'm just testing the bad part that malfunctioned on the board.
I connected just a power and hooked the oscilloscope to the output.
That the first time ever I have encountered with the problem with the
ceramic oscillator!
So , your repairing?
 
L

legg

Jan 1, 1970
0
I encountered with very strange problem with a ceramic crystal
oscillator.
It took a long time to recreate the problem.
When a power supply voltage is turned on first time there is no output
frequency. When the power supply is turned off and on again the
frequency appears.
You can see it on the video here.
Any suggestions?
The vendor doesn't know why it happens. :(

Looked like it actually was encouraged to start as the first
application of power was in the process of being removed.

Try delaying the enable signal. You don't indicate how it is being
connected - assume currently a short to appropriate logic.

Check it's spec for minimum/maximum dv/dt on the supply pin.
Check it's application supply voltage range.

RL
 
E

Eeyore

Jan 1, 1970
0
Mig said:
I encountered with very strange problem with a ceramic crystal
oscillator.
It took a long time to recreate the problem.
When a power supply voltage is turned on first time there is no output
frequency. When the power supply is turned off and on again the
frequency appears.
You can see it on the video here.
Any suggestions?
The vendor doesn't know why it happens. :(

The vendor is useless in that case. Find a new vendor.

Is that an oscillator *module* btw or one you built with the vendor's crystal ?

Graham
 
M

Mig

Jan 1, 1970
0
The vendor is useless in that case. Find a new vendor.

Is that an oscillator *module* btw or one you built with the vendor's crystal ?

Graham

The part is a module. So there is no option for tweaking gain or
something else.
So far there were no problems with this vendor. But there is always
first time. :(
I have not heard from him since I sent him a link with the video.
I have already ordered samples form another company.
 
E

Eeyore

Jan 1, 1970
0
Mig said:
The part is a module. So there is no option for tweaking gain or
something else.
Understood.


So far there were no problems with this vendor. But there is always
first time. :(
I have not heard from him since I sent him a link with the video.
I have already ordered samples form another company.

That sounds like the best idea.

Graham
 
I encountered with very strange problem with a ceramic crystal
oscillator.
It took a long time to recreate the problem.
When a power supply voltage is turned on first time there is no output
frequency. When the power supply is turned off and on again the
frequency appears.
You can see it on the video here.
Any suggestions?
The vendor doesn't know why it happens. :(

That is the geekiest video I ever saw on youtube. ;-)

I see that you are powering up a bench supply to start the module.
Often these bench supplies have a soft start feature. Your module may
not like the supply to be ramped slowly. Try leaving the supply on and
just connecting the DC to the module, that is, hit it hard.
 
P

Phil Hobbs

Jan 1, 1970
0
Mig said:
I encountered with very strange problem with a ceramic crystal
oscillator.
It took a long time to recreate the problem.
When a power supply voltage is turned on first time there is no output
frequency. When the power supply is turned off and on again the
frequency appears.
You can see it on the video here.
Any suggestions?
The vendor doesn't know why it happens. :(

Startup problems are as common as dirt.

Most oscillators work in a large-signal regime where the active devices
are nonlinear. Thus the average gain, impedance level, and feedback are
all different when the oscillator is running, compared with the same
circuit in a quiescent state.

The feedback loop may well be stable at small-signal conditions and only
oscillatory at large signal conditions. If the power supply transient
is quicker than the bias time constant of the oscillator, it'll find
itself in a large-signal condition at power-up, which will get the
oscillator going and mask the startup problem. It's really important to
test oscillators under a wide variety of turn-on conditions, including
very slow ramps.

It's also quite possible for oscillators to have too much feedback, in
which case you get all sorts of distortion and self-modulation rather
than a nice CW sine wave. ALC oscillators adjust their loop gain based
on oscillation amplitude, and thus tend to avoid both kinds of problem
(as well as being much quieter).

I gather that your power supply is producing different turn-on
transients, depending on how long it has been switched off. From the
symptoms, it appears that when it's been off long enough for the filter
caps to have discharged, the turn-on is slower than when you turn it off
and then on again, and the difference is enough to expose the startup
problem.

Cheers,

Phil Hobbs
 
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