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Mitigating Signal Reflection

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?

Reply to
Dan
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The first thing I would suspect is external-noise pickup, possibly from a local AM radio station, or switching noise from electronics in the area (e.g. switching power supplies, DC to DC converters, microprocessor or microcontroller circuits, etc.)

A meter of wire makes a pretty good antenna, and there's a lot of RF noise and AM signal power floating around in the air these days.

You may be able to eliminate this (or reduce it to tolerable proportions) by distributing the clock signal over a shielded coax cable, rather than a bare wire.

Reply to
Dave Platt

Have you earthed the oscilloscope to the circuit you are testing?

Reply to
Liz Tuddenham

There's a possibility the fault could arise through improper use of the level shifter, making it tip into self-oscillation when a load is connected. This is not uncommon with voltage regulators as well. I would suggest you strictly follow the recommendations on the data sheet in regards to any ancillary components this device may require.

Reply to
Cursitor Doom

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

Reply to
legg

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