Re: Fast sampler

On 3/11/25 11:12 AM, Phil Hobbs wrote:

On 2025-03-09 19:22, Tom Del Rosso wrote:

Phil Hobbs wrote:

Hi, All,
>
Late last year we did a fast sampler/TDR with nice clean 60 ps edges.
>
We're gearing up to actually sell them, so I did a short technical
writeup on the design, which may be of interest.
>
<https://electrooptical.net/News/a-high-performance-time-domain- reflectometer>
>
Cheers
>
Phil Hobbs

>
Why is a LASER ruler that can measure distances in air with 2mm accuracy
$16,
>
and an OTDR for measuring fiber $600?
>

 Well, the OTDR needs a fiber-coupled laser, for one thing, and a decent TIA.  Also as John says, it's a time-domain instrument.  A laser ruler can just be a diode laser with a monitor photodiode, a collimating lens, a simple TIA and a micro with built-in ADC.
 You put a small (1-3 mA) current ramp on the laser, and look at the beat signal coming out of the monitor photodiode.  The frequency gives you the round-trip delay.  This sort of laser feedback measurement can be pretty good if the diode stays reasonably single-mode.
 I have no idea how the $16 ones do it, but if I were building one, that's the first thing I'd try.
 Cheers
 Phil Hobbs
 

Short distance laser rangefinders can be implemented with the integrated time-of-flight sensors now being used in cell phones.
https://www.st.com/en/imaging-and-photonics-solutions/vl53l0x.html#overview
$5 single quantity from Digikey.
kw