[time-nuts] Linear Interpolator

Magnus Danielson cfmd at bredband.net
Fri Jun 30 08:58:27 EDT 2006

From: "Stephan Sandenbergh" <stephan at rrsg.ee.uct.ac.za>
Subject: Re: [time-nuts] Linear Interpolator
Date: Fri, 30 Jun 2006 14:02:11 +0200
Message-ID: <002c01c69c3d$053bc8a0$401c9e89 at Stephan>

> Hi Ulrich,


> Thanks for the tip. And, also many thanks to Magnus for introducing me to
> the concept of Time-to-Digital conversion. It is a brilliant and yet so
> simple technique. (Until yesterday, I blissfully believed that a fast
> clocking counter was one's best bet.) 

Indeed. Once you understood the basic concept, the particular interpolating
technique you choose may vary as you see fit.

> I also read the article posted earlier by Tom van Baak (Thanks Tom! This is
> indeed a very comprehensive article.) It turns out that you can implement a
> very elegant linear interpolator using a digital delay line inside a FPGA.
> It is called the Vernier technique. From the article I understand that
> resolutions of between 10s and 100s of picoseconds have been achieved for
> various designs.
> Has anyone else used this Vernier technique with delay lines? I seems pretty
> neat to me.

It's what makes the HP5371A/HP5372A tick, it cranks out 200 ps resolution that
way and keep counters at a mear 500 MHz. The HP5370A use a dual oscillator
Vernier trick instead.

It can be a bit of a challenge to get the FPGA to perform reliably thought.
You could do a similar thing with a single delay-line but dual clocks of near
same frequency. That might be a bit more reliable than the dual delay-line

> It means my hardware doesn't need to change. A software update will do the
> trick :)   

Hehe... ;O)


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