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From: KevinJ93 <kevin_es@whitedigs.com>
Newsgroups: sci.electronics.design
Subject: Re: Fast sampler
Date: Tue, 11 Mar 2025 19:02:20 -0700
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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