Hello,

I have got the following basic problem.
I have a Abracon ACOL crystal clock oscillator (3.3VDC HCMOS/TTL
compatible). When measuring the clock output using an oscilloscope, I
get the correct frequency, but the waveform is not a rectangle. It's
more a very overshooted rectangle. The datasheet states, that the
rectangle waveform should be alternating from 90%VDC and 10% VDC.
The sampling rate of the oscilloscope is sufficient.

Are there any special needs when testing a clock oscillator. There are
different test circuits for TTL and HCMOS. What's the difference
between these test circuits? Or maybe the overshooting is a normal
behaviour?
Hopefully there's someone around with some more experience than I have.

Datasheets of the unit discussed:
http://www.abracon.com/Oscillators/acol-achl.pdf

Test circuits:
http://www.abracon.com/Support/appendix-b.pdf

Best regards,
Stefan.
------------------------------------



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----- Original Message -----
From: "scientificsteve"
To:
Sent: Friday, September 26, 2008 8:58 PM
Subject: [msp430] Measure crystal clock oscillator with oscilloscope
> Hello,
>
> I have got the following basic problem.
> I have a Abracon ACOL crystal clock oscillator (3.3VDC HCMOS/TTL
> compatible). When measuring the clock output using an oscilloscope, I
> get the correct frequency, but the waveform is not a rectangle. It's
> more a very overshooted rectangle. The datasheet states, that the
> rectangle waveform should be alternating from 90%VDC and 10% VDC.
> The sampling rate of the oscilloscope is sufficient.
>
> Are there any special needs when testing a clock oscillator. There are
> different test circuits for TTL and HCMOS. What's the difference
> between these test circuits? Or maybe the overshooting is a normal
> behaviour?
> Hopefully there's someone around with some more experience than I have.

Is the probe ground close to the oscillator ground?

Leon
------------------------------------



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Also, check if the probe is correctly calibrated (the scope might have
a square wave output for that purpose).
Just yesterday a guy in the lab had the same problem WITH A 1KHz
SIGNAL. Using the other probe, there was no overshoot at all.

Michael K.

--- In m...@yahoogroups.com, "Leon" wrote:
>
> ----- Original Message -----
> From: "scientificsteve"
> To:
> Sent: Friday, September 26, 2008 8:58 PM
> Subject: [msp430] Measure crystal clock oscillator with oscilloscope
> > Hello,
> >
> > I have got the following basic problem.
> > I have a Abracon ACOL crystal clock oscillator (3.3VDC HCMOS/TTL
> > compatible). When measuring the clock output using an oscilloscope, I
> > get the correct frequency, but the waveform is not a rectangle. It's
> > more a very overshooted rectangle. The datasheet states, that the
> > rectangle waveform should be alternating from 90%VDC and 10% VDC.
> > The sampling rate of the oscilloscope is sufficient.
> >
> > Are there any special needs when testing a clock oscillator. There are
> > different test circuits for TTL and HCMOS. What's the difference
> > between these test circuits? Or maybe the overshooting is a normal
> > behaviour?
> > Hopefully there's someone around with some more experience than I
have.
>
> Is the probe ground close to the oscillator ground?
>
> Leon
>

------------------------------------



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