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mekpeacenfood
Joined: 23 Jul 2008
Posts: 1
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 23 Jul 2008 4:45 Square wave from sine -- high stability |
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Hi, we have a very accurate sine wave source that we'd like to use to sync our whole apparatus with. However, not all components take a sine input--some use a trigger port and want a square wave.
What is the best way to convert a very clean 10 MHz sine wave to a square wave? As a complication, it will need to drive 50 ohms ~1V.
It seems like such a common task--surely everything from oscilloscopes to timing standards themselves need this. What is the accepted strategy? Is a schmitt trigger alone enough, or will phase jitter still be more than a couple ns? If so, what can I add to "take it to the next level"?
Last edited by mekpeacenfood on 23 Jul 2008 19:36; edited 1 time in total |
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FvM
Joined: 22 Jan 2008
Posts: 2487
Helped: 409
Location: Bochum, Germany
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| 23 Jul 2008 17:17 Square wave from sine -- high stability |
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| A fast comparator would be the usual solution.
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biff44
Joined: 24 Dec 2004
Posts: 1254
Helped: 160
Location: New England, USA
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| 23 Jul 2008 18:46 Re: Square wave from sine -- high stability |
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I wouldn't use a comparator unless timing is not critical! The slightest voltage noise at the comparator threshold will turn into clock phase noise.
I would make sure the sine wave is big (linearly amplify), and then either clip it at ground and +Vcc with very fast schottky diodes, and then buffer with a very fast (1 ghz) CMOS gate.
You might get away with just driving the sine wave, AC coupled, into the appropriate gate--without the diode clipping. sn74lvc1g17dbvr looks like a good one to use.
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FvM
Joined: 22 Jan 2008
Posts: 2487
Helped: 409
Location: Bochum, Germany
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| 23 Jul 2008 19:42 Re: Square wave from sine -- high stability |
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| The suggestion should be verified by comparing real device data. I assume, that the said very accurate sine wave has a sufficient amplitude anyway. In this case I insist on my opinion, that a fast comparator (as ADCMP551 or similar) promises the best performance in most cases. Fast CMOS gates or LVDS receiver can be also used, but a less exactly defined threshold and higher temperature dependency of treshold voltage and delay may be a disadvantage.
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sergio mariotti
Joined: 22 Dec 2003
Posts: 454
Helped: 38
Location: Italy
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| 02 Aug 2008 20:24 Re: Square wave from sine -- high stability |
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In my opinion the lowest jitter circuits are proposed by atomic clock manufactures.
Take a look pag 17 of the following doc
http://www.2917.com/EBAY-images/LPRO-101/LPRO-101.PDF ( or google "LPRO User Manual")
You have to pay attention not only to phase noise and jiiter; drift is also important.
In order to minimize drift, the circuit board should be electrically short as possible and thermostatic.
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