Re: A Question For The Group

Craig Sawyers <c.sawyers@...>
 

I'm thnking now, would it be more accurate and easier to simulate a
10X scope probe and of course not use the 50 ohm termination. I'm not
real happy with the waveform I'm getting right now with the TI
device. It's not an accurate reproduction at the higher frequencies,
I think because of the 10X attenuation circuit leading into the input
of the device.
The thing to do is use a probe adaptor. Tek used to supply these with some
of their probes. Looks like a little BNC, but the receptacle takes the
probe tip. You solder the centre pin to the signal, and the outer to the
ground plane (you've got one of those - right?). When you plug the scope
probe in, there are virtually no additional errors arising from tip grabber
and ground clip inductance, and you get a very clean signal.

You can do the same thing with a FET probe too, and reduce the loading to
one or two pF.

If the circuit has to look into 50 ohms, load the circuit locally with a
50-ohm resistor (a surface mount component connected between the IC pin and
ground plane is ideal), then probe the circuit as above.

Craig

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