N2809A Datasheet, PDF (3/11 Pages) Keysight Technologies – Bandwidths up to 33 GHz

03 | Keysight | PrecisionProbe for Bandwidths up to 33 GHz - Data Sheet
Background – PrecisionProbe
Probes and cables have inherent loss and variation.
The loss at times can be substantial, or merely different
enough from the nominal to cause variation in measurements.
To compensate for the inherent loss, oscilloscope vendors
use probe correction via DSP. The vendor uses a “golden”
model and base, all compensation/correction on the single
model. While this strategy solves some of the loss and
variability, it also still means that if a probe’s characteristics
have changed/drifted or were not close to the model to
begin with, the compensation is no longer correct for the
probe. There are also a myriad of probe heads to attach
to probe amplifiers for maximum accuracy when every
combination must be measured. The end result is that
you can get unwanted inaccuracies or probe to
probe variability.
You also use custom probes and probe heads. While this
provides great convenience for you it means that the
oscilloscope vendor no longer can even provide a “golden”
system. Meaning that custom probes are uncorrected and
inaccurate, but convenient.
You may also want to add something between the probe
amplifier (such as Keysight’s 30 GHz N2803A) probe
amplifier and (such as Keysight’s 30 GHz N5444A browser
probe head), including a cable to add length or a switch
matrix. This adds inaccuracies as the probe amplifier and
browser head are compensated to the model, the newly
created probe now has no model. The result is that you
must except the inaccuracies that have been added or try
to characterize the additional element in the probe link.
While accepting both of these trade-offs can be sufficient,
it is time consuming to evaluate the element every time
and not characterizing the element causes loss of mar-
gins (including higher jitter, smaller eyes, and slower rise
times). This can also be the cause of differences between
numbers measured in simulation and the number actually
achieved in actual measurements.
Figure 1: Probe browser with a non-standard pitch
Figure 2: Image of custom probe
Figure 3: Image using LW ZIF Head