Mini USB signal measurement.

In our product we are using Mini USB for flashing purpose. Speed is 480Mbits/s. I'm using Lecroy PP020 500MHz for measuring the D+ and D- signals in USB. But the ringing is High, I'm not able to get a more defined Square wave to conclude. I have given shortest Ground for probe as well. what is the reason for High Ringing in Output.

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0 baldengineer over 1 year ago

In addition to the loading of the passive probe, it doesn't have enough bandwidth. Using a 500 MHz signal to look at an (effectively) 480 MHz signal means seeing only the fundamental sine wave. The edges of those signals contain significantly higher frequency content.

For the 3rd harmonic, you need at least 1.5 GHz (both scope and probe.)

And, I believe the USB Compliance Spec requires 2.5 GHz for High-Speed devices.

For High-Speed devices (and faster) you need active probes.
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0 jc2048 over 1 year ago in reply to baldengineer

Isn't alternate ones and zeros at 480Mbps a fundamental of 240MHz?
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0 jc2048 over 1 year ago in reply to baldengineer

Isn't alternate ones and zeros at 480Mbps a fundamental of 240MHz?
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0 baldengineer over 1 year ago in reply to jc2048

*facepalm*. Yes. You are right! The fundamental is 1/2.

But. Even at 240 MHz, the 3rd harmonic is around 720 MHz. So, 500 MHz still isn't enough bandwidth to reconstruct a square wave.
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