Keysight Technologies 3458A Guide D'utilisation page 499

Figure E-14
Finally, the accuracy of the measurement itself, although not often discussed with
digitizers, is related to the reference accuracy of the 3458A. For static and
dynamic measurements, the absolute accuracy actually exceeds the dmm's
resolution. And, in terms of long term drift, the absolute error is less than 7 ppm
per year.
Trigger and timebase errors
The timebase, a precision temperature compensated quartz crystal, has its drift
and jitter which will affect the amplitude measurement of the input signal. But,
these tend to be very small - less than 50 ps. Hence, the clock accuracy and jitter
do not really affect the measurement within the measurement bandwidth of the
3458A. The timebase jitter error is not cumulative; therefore each sample point
has only its own jitter error and not the combined jitters of previous sample points.
The effects of all the time axis errors are shown in
The trigger error is orders of magnitude greater than timebase error and jitter. Two
effects cause this. The 3458A has no delay line, so there is a trigger latency, a time
delay between the trigger and the commencement of the measurement, that is
fixed by the firmware, the clock, and the timing circuits. It is specified to be less
than 175 ns for an external trigger. The accuracy of the trigger can also be
affected by noise on the trigger signal and time interpolator variation between
measurements. This is of the order of 50 ps as well except in very noisy cases,
where it is advisable to use the 3458A's trigger filter which reduces the bandwidth
of the trigger circuit to a nominal value of 70 kHz.
Keysight 3458A User's Guide
High Resolution Digitizing With the 3458A
Amplitude roll-off of the 3458A multimeter for its two different
measurement paths.
Figure E-15.
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