[time-nuts] Zero-Crossing Detector Design?

Bob Camp lists at rtty.us
Thu Jul 19 22:15:18 UTC 2012


Hi

The numbers change rather dramatically if you are looking at the 1 to 10 Hz sine wave out of a beat note system…

Bob

On Jul 19, 2012, at 3:47 PM, Bruce Griffiths wrote:

> The problem of optimal zero crossing detector design was essentially solved by Oliver Collins in the 1990's.
> Essentially a series of cascaded limiter stages with appropriate gain and bandwidth distribution are used.
> With a 10MHz 1V rms signal only 2-3 stages suffices.
> However unless you need fs jitter less complex zero crossing detectors should suffice.
> 
> 1) a comparator (or line receiver) based design should achieve sub 10ps jitter.
> 
> 2) AC coupling to the input of a CMOS (AC04, AHC04 LVC04) should achieve a jitter of 1ps or less
> 
> 3) A simple differential pair with AC coupled emitters (reduces asymmetry due to component tolerances ) is capable of sub ps jitter.
> 
> There is a spreadsheet to assist design of Collins style zero crossing detectors at:
> 
> http://www.ko4bb.com/~bruce/ZeroCrossingDetectors.html <http://www.ko4bb.com/%7Ebruce/ZeroCrossingDetectors.html>
> 
> Bruce
> 
> 
> paul swed wrote:
>> you can search time-nuts there has been a number of very good discussions
>> on this.
>> Sorry to say how you search is equally a good question.
>> 
>> On Thu, Jul 19, 2012 at 3:19 PM, Chris Hoffman, KG6O<cq.kg6o at gmail.com>wrote:
>> 
>>   
>>> Thank you, Azelio! I don't suppose there's an impromptu FAQ page out
>>> there, is there?
>>> 
>>> -CH
>>> 
>>> On Jul 19, 2012, at 11:58, Azelio Boriani<azelio.boriani at screen.it>
>>> wrote:
>>> 
>>>     
>>>> This is sort of a FAQ: the argument was already discussed here. One of
>>>>       
>>> the
>>>     
>>>> most interesting idea (in my opinion) is to use an RS485 line receiver
>>>>       
>>> like
>>>     
>>>> the ST3485, MAX483, ADM485. They are actually transceivers so they must
>>>>       
>>> be
>>>     
>>>> tied permanently in RX. Since they are differential you can also put a
>>>>       
>>> 1:1
>>>     
>>>> (or a 1:4 to raise the level) transformer to isolate the input too.
>>>> 
>>>> On Thu, Jul 19, 2012 at 6:03 PM, Chris Hoffman<cq.kg6o at gmail.com>
>>>>       
>>> wrote:
>>>     
>>>>       
>>>>> Can anyone suggest a good reference design for a zero-crossing
>>>>>         
>>> detector? I
>>>     
>>>>> am trying to home an ADC sampler trigger to the 1VRMS (50ohm) 10MHz sin
>>>>> from my XL-DC... And now I'm thinking that I should just home the uC
>>>>>         
>>> clock
>>>     
>>>>> to it, as well.
>>>>> 
>>>>> Essentially, I believe that I'm looking for an efficient, stable, and
>>>>> accurate sine-to-square converter... and I'll welcome any advice in this
>>>>> area.
>>>>> 
>>>>> This may also be used in a 1KHz 5Vpp IRIG-B decoder... I don't feel like
>>>>> rectifying the signal, to be honest. I want to try to keep a smaller
>>>>>         
>>> BOM,
>>>     
>>>>> sense the waveform primarily, and crunch numbers inside the uC.
>>>>> 
>>>>> 
>>>>> -CH
>>>>> 
>>>>> Chris Hoffman
>>>>> cq.kg6o at gmail.com
>>>>> http://ar.ctur.us
>>>>> 
>>>>> 
>>>>> 
>>>>> 
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>>>>>         
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> 
> 
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