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From: legg <legg@nospam.magma.ca>
Newsgroups: sci.electronics.repair
Subject: Re: Mitigating Signal Reflection
Date: Fri, 22 Mar 2024 12:55:01 -0400
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On Mon, 18 Mar 2024 00:12:14 GMT, Dan <dan@nospam.invalid> wrote:

>I'm new to electronics and I'm hitting an issue beyond my skill set. I
>should start by saying I'm not 100% sure signal reflection is the issue,
>but it's my best guess.
>
>I have a 3.3V clock signal that I'm trying to convert to 5V. The clock
>speeds are sub 100 kHz. I'm using a TI level shifter, TXS0108E. Looking
>at the signal on a scope, it's a clean signal on the input and output
>side when I don't have anything connected on the output side.
>
>When I hook up the clock signal on the output side, over an
>approximately 1 meter wire the signal on the scope is full of noise. The
>scope also says the frequency is much higher than one the input signal
>should generate. I see the noise push through to the input side. I'm
>assuming this is because the level-shifter is bi-directional.
>
>I've tried a few failed solutions, like using a diode to try and block
>out the reflections, but so far no luck.
>
>Any advice on how to deal with this?

Using a twisted pair for the signal might make sense. Running the 
wire close to the system's metal container, or test bed ground plane 
is also advised.

Where's the ground lead on the scope connected when you're 
making these measurements? It can introduce gound loops.
If the noise/problem goes away when the the scope's disconnected 
it's an indicator.

RL