EEVblog® Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: qczech on May 27, 2013, 03:19:35 pm
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Hi.
Warning, this question is very vague and conceptual.
I've been presented the following problem:
A rubidium oscillator needs to drive a 50 Ohm load, but is unable to do so because it has a slow rise time and a small amplitude.
I have devised a simple FET amplifier to increase the amplitude and a comparator to decrease rise time.
However I am told that there might be a better way of decreasing the rise time than with a comparator. What might it be?
I will make measurements tomorrow and try to give some numbers.
Regards.
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Apart from the question what the risetime got to do with the ability to drive a 50 Ohm load I think a comparator would be just fine, assuming we are talking square waves isn't it? And while you have the comparator, why do you need the FET amplifier? If you are talking 5 volt try to find a comparator with 100 mA drive current and you are done.
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Hello, if your Rb has a sinewave output you can find simple
and tried clock shaping circuits, based on comparator, or
filter + logic gate, or isolated, dpending on your needs:
http://www.ko4bb.com/Timing/ClockShaper.php (http://www.ko4bb.com/Timing/ClockShaper.php)
http://www.ko4bb.com/dokuwiki/doku.php?id=precision_timing:clock_shapers (http://www.ko4bb.com/dokuwiki/doku.php?id=precision_timing:clock_shapers)
http://www.ko4bb.com/~bruce/CLKSHPR.html (http://www.ko4bb.com/~bruce/CLKSHPR.html)
I've used this circuit, Q4 Q8:
http://www.flickr.com/photos/14336723@N08/8297438155/# (http://www.flickr.com/photos/14336723@N08/8297438155/#)
If your source is an FE5680A, it's output it's a digital signal
filtered by an RC filter, you can open it and disconnect the
capacitor to have your nice squarewave, some resources:
http://www.ko4bb.com/dokuwiki/doku.php?id=precision_timing:fe5680a_faq (http://www.ko4bb.com/dokuwiki/doku.php?id=precision_timing:fe5680a_faq)
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Hi,
There are two ways to do this:
1) Is to use some form of comparator. Apply a fixed voltage to one input and the sinewave to the other input.
2) The second way is to amplify the signal until it clips.
The advantage of the second method is that it offers reduced jitter.
There are parts that are specially designed for this:
http://www.linear.com/product/LTC6957-1 (http://www.linear.com/product/LTC6957-1)
You should also read the design note:
http://cds.linear.com/docs/en/design-note/dn514f.pdf (http://cds.linear.com/docs/en/design-note/dn514f.pdf)
Phase noise on the a sinewave becomes jitter on the edges of a squarewave so the terms are similar.
Jay_Diddy_B
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Thank you for your replies.
The Rubidium standard used is the GRCLOK-1500 (datasheet: http://www.spectratime.com/documents/iSync_GRClok-1500_Spec_060513.pdf (http://www.spectratime.com/documents/iSync_GRClok-1500_Spec_060513.pdf))
It outputs a sine wave. The output impedance of the 10MHz clock is 50 Ohm +- 20%, 60 Ohms taking worst case scenario. The datasheet says that it is 0.5Vrms. I have made measurements on the unit that I have and the signal is 3.125V peak to peak.
The clock needs to drive three 50 Ohm loads so an equivalent of a ~16 Ohm load. It also needs to be converted into a square wave with a rise time of around 10 ns.