[time-nuts] Re: Input stage for time interval counter

[Bruce Griffiths]

The eval board for the LTC6957 uses capacitive coupling. However, the transformer coupled circuit shown in the datasheet allows operation over a wider input signal level range. Although intended for 10Mhz inputs it should work well at 5MHz as well. 

Bruce
> On 01/12/2022 09:52 NZDT Michael Fahmie via time-nuts <time-nuts at lists.febo.com> wrote:
> 
>  
> I would go with the transformer input. It would remove any common mode
> current flowing on the inputs that might 'modulate' the switching
> thresholds.
> -Mike-
> 
> 
> On Wed, Nov 30, 2022 at 12:41 PM Hans-Georg Lehnard via time-nuts <
> time-nuts at lists.febo.com> wrote:
> 
> > Hi all,
> >
> > I am currently working on a 2 channel time interval counter. It should
> > measure frequencies from 5 to 20 MHz. And hopefully have a resolution
> > about 1E-13 at 0,1s to measure HP10811 OCXO stability.
> >
> > For inputs should I use  UNBAL Rf transformers 1:4 (1:16) or drive the
> > LTC9657 directly.
> >
> > Thanks for your suggestions
> >
> > hgl
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