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First Measurements

A project log for 6 GHz Sampling Oscilloscope

Maybe 5 or 7, but what's a GHz or two between friends?

Ted YapoTed Yapo 08/23/2019 at 14:310 Comments

I have been told that at a certain oscilloscope manufacturer the first measurement with a new scope design is sometimes called "green on screen," like "first light" for telescopes and "first ping" for routers. This is the first waveform captured with the first prototype sampler:

It's the output from a pulse generator made with a 74LVC2G74 flip-flop with the data line tied high and Q-bar output tied to the Reset-bar input. I'm using a pulse generator like this (but with faster 7 4AUC logic) in another sampler design. Don't use this in your logic circuits, people, it's just for analogy-stuff :-)

For reference, here's the output of the same circuit captured with a Tektronix 11801B scope and 20 GHZ SD-24 head:

There is an extra wiggle on the left baseline of the trace from my sampler. The test setup to capture these two traces was not identical, and I suspect there may be a ground-bounce issue causing the difference. It needs some further investigation.

Overall, however, the result doesn't look too bad for a first test. The waveforms are pretty close otherwise, and the result would certainly be usable in some cases. I know there are some reflections happening in the front end which are sure to corrupt the waveform somewhat, and these may be responsible for some of the small differences here, but I think the result shows promise.

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