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Measuring risetimes with Infiniium 54854A

Question asked by esz-ag on Feb 3, 2009
Latest reply on Feb 5, 2009 by marowley
In terms of estimating our own uncertainty in measuring the risetimes of fast square pulses (960ps - 150ps) with an Infiniium 54854A, we discovered an extensive dependence of the measuring result on vertical, horizontal and especially offset setting with this scope. Solely the shifting of the offset within one vertical setting effects about 7% of variation in reading. Furthermore the average value of these readings often is even a little faster than the real signal.
Can you give us some clues to isolate the origin of this pecularity? Thus it would be easier for us to achieve a better repeatability and uncertainty in measurement with this instrument.

This Problem also exists when it comes up to determine the scope's own risetime with a fast pulse of 66ps. Normally we can speak of a relation between risetime and -3dB-Bandwidth of 0,35 and 0,4 when infering from -3dB-bandwidth to risetime. Does this fit for the Infiniium 54854A too, and is there a dependence on the signal's velocity (concerning risetime/frequency)?

To discover this issue we use squarewave pulses with 1 Vpp, 1 MHz and variable risetime as mentioned above.
So the pivotal question is now, what are the best settings to achieve the best repeatability and the lowest uncertainty and error in measurement?

Thank you for your support