[time-nuts] ? phase comparison or other device

Dr Bruce Griffiths bruce.griffiths at xtra.co.nz
Sun Jul 1 18:02:44 EDT 2007


Bob Paddock wrote:
>> These devices are a little noisy below 100Hz.
>>     
>
> Rather than constantly battle the "there is to much noise", what are
> your thoughts on deliberately injecting out-of-band noise?
>
> As an example:
> http://www.analog.com/UploadedFiles/Application_Notes/319765654AN-410.pdf
> "Overcoming Converter Nonlinearities with Dither"
>
>   
>> The distortion produced by a diode clamp is immaterial when one is only 
>> interested in the zero crossing time.
>>     
>
> It depends on where the harmonics fall.
>
>
>   
Bob

What is the application for which you want to use injected out of band 
noise?
Since the performance of a well designed zero-crossing detector is 
equivalent to a 25 bit ADC when locating the zero-crossing, it will be 
difficult to replicate this performance using a lower resolution ADC 
even combined with out of band dithering.

In practice, diode clamp circuit distortion in a zero-crossing detector 
isn't an issue.

Bruce



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