[time-nuts] External clock for Analog to Digital Converter in GPS Rx front-end

[Dr Bruce Griffiths]

Bilal Amin wrote:
> ----- Original Message ----- 
> From: "Dr Bruce Griffiths" <bruce.griffiths at xtra.co.nz>
> To: "Discussion of precise time and frequency measurement" 
> <time-nuts at febo.com>
> Sent: Friday, March 02, 2007 6:10 PM
> Subject: Re: [time-nuts] External clock for Analog to Digital Converter in 
> GPS Rx front-end
>
>
>   
>> Bilal Amin wrote:
>>     
>>> Hi Everyone,
>>>
>>> I am working on Jitter in Analog to Digital Converters(ADCs) for GPS 
>>> receiver front-end. I am trying to setup an experiment to see the effects 
>>> of jitter in real time ADCs. I have an ADC evaluation board with external 
>>> clock input for sampling (i.e Sampling clock). Now I want to produce a 
>>> self created jittery signal to see the effects of jitter in ADC. Can 
>>> anyone out there have any idea(s) how I can produce a real time clock 
>>> signal with "variable jitter" for the input of external clock? Producing 
>>> a simple clock signal (i.e. without jitter) is straight forward with the 
>>> help of any signal generator but a clock signal with "variable jitter" is 
>>> a problem.
>>>
>>> Thanks for your help.
>>>
>>> Cheers
>>>
>>> Bilal
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>>>
>>>
>>>       
>> Bilal
>>
>> All you have to do is add sufficient noise to a sinewave clock.
>> The clock shaping circuitry will then convert the noise to timing jitter
>> at the zero crossings.
>> All you need is a suitable source of wideband noise.
>>
>> Bruce
>>
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>>     
> Hi Bruce,
>
> Thanks for your email.Adding noise to a sine wave is not that straight 
> forward I guess. Do you think a comparator works for this? 
>
>
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>   
Bilal

You can easily add noise to a sinewave, for example a hybrid combiner 
can be used to combine the output of a sinewave generator and a noise 
source.

It is also possible to connect a noise source to one input of a 
comparator whilst connecting the sinewave to the other input of the 
comparator.

Selected current starved zeners can make very good wideband noise 
sources, buffer and amplify/attenuate as required.

Bruce