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Old 28th March 2003, 09:50 AM   #21
A 8 is offline A 8  Sweden
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Thx Guido,

I am a bit slow...get it now.

Actual testing would be really interesting!
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Old 28th March 2003, 12:08 PM   #22
tiroth is offline tiroth  United States
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There are two simulataneous conversations going on in this thread!

When talking about active XO, there is no way to get a square wave through both halves because we are intentionally frequency limiting. Now, you may be interested in the summed response looking like a square wave. In addition to preserving the phase relationship, you want a high "slew rate" for the high-pass capacitors. This is NOT a problem at audio frequencies.

The low pass is a little trickier but generally it is possible to have a low enough high pass on the coupling cap that there is not much tilt. It is questionable how low you want to go because you will just waste power and potentially get IMD from subsonics.

In conclusion, for AUDIO FREQUENCIES, there is not much problem with coupling caps if chosen properly.

Guido,

I think we are in agreement. I was just trying to steer the thread back to what I thought was the original subject.
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Old 28th March 2003, 12:49 PM   #23
A 8 is offline A 8  Sweden
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This thread is about square waves of 12 Mhz to 32 Mhz.
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Old 28th March 2003, 01:27 PM   #24
tiroth is offline tiroth  United States
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My apologies.
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Old 28th March 2003, 01:37 PM   #25
A 8 is offline A 8  Sweden
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Dont worry, I know the XO thing probably consfused many.

Cheers
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Old 28th March 2003, 01:49 PM   #26
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Originally posted by A 8
Dont worry, I know the XO thing probably consfused many.

Cheers
Hi all,

Yes, confusing :-)

C coupling and its' habbits principally do not depend on frequency, however the appplication, reaction and sensitivity does.
Yes, I measured a lot, but do not directly give away the results, if you do not mind, as lots of time and effort where put in.

all the best
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Old 28th March 2003, 02:32 PM   #27
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Default Who among you actually carried out easurements on.......

I have, but I no longer have access to all the equipment that you still do, Guido.

So I have to come up with different approaches. In any case, you are right.....it is a lot of work, and most people here don't have our capabilities.

Jocko
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Old 28th March 2003, 02:37 PM   #28
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Quote:
and most people here don't have our capabilities
They probably have in another area.
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Old 28th March 2003, 02:57 PM   #29
alvaius is offline alvaius  Canada
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Sometimes passing perfect square waves is not the best thing to do. That means higher EMI, higher transient currents, etc. that could create their own problems. I have experienced cases where a bit of slew rate limiting has resulted in better system performance, though not specifically in audio, though the output gates on some logic families (on the output of the XO) are prone to ground bounce and a little bit of slew rate limiting could help the final effect.

However, what the issue here may be is more a matter of implementation. If the output of the XO is simply a sine wave (which internally they all are close to at some point), then AC coupling and limiting the bandwidth is not really an issue.

A 8, did you have a specif application or instance in mind?

Alvaius
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Old 28th March 2003, 03:01 PM   #30
jwb is offline jwb  United States
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I don't have the equipment to carry out jitter measurements either, but I do have a spectrum analyzer and I've been experimenting with the oscillator Jocko posted (the one with the common-base amp to pick off the signal) and the output Q is higher without the coupling caps. I was using a 20pF mica, but if I just jumper it the Q improves. Presumably a higher Q on a sine oscillator is always desirable.

The coupling cap is not needed as long as the common mode signal is within the input range of the next thing downstream. In this case it is a 5V comparator and the common mode is right in the middle at about 2.5V.

-jwb
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