Measurement Mode - Tektronix 11801C User Manual

Measurements

Measurement Mode

Measurements may be taken in software mode, hardware mode, or statistics
mode. In software mode, measurements are taken from the digitized trace
data record, the same data that forms the trace on the display. Software
mode is the default.
In hardware mode, measurements are taken from the analog signal output
from the sampling head before it is digitized and assembled into a trace
record. The 11801C uses special timer circuits to take hardware measure
ments. The advantage of hardware measurements is that they are per
formed faster than software measurements.
In statistics mode, measurements are taken from color graded waveform
data and are based on histograms computed at the crossing levels. You can
use statistical measurements to measure random" data such as eye dia
grams. Statistics mode also provides jitter and noise measurements, and
can be more accurate for other measurements on waveforms with significant
jitter or noise.
Statistics mode can be selected only in color graded display mode. Because
the color graded database does not distinguish between traces, statistical
measurements are limited to one trace per graticule. (Stored traces may be
left on the display; they are ignored by the statistical measurement algo
rithm.) Whenever making Statistics Mode measurements of an eye pattern
trace, set the Eye Pattern selector in the Measurements pop up menu to
On.
All measurements, except the three Frequency Domain measurements, in
the Measurements pop up menu can be taken as statistical measurements.
In software mode, all measurements except Noise, SNR, and Jitter are
available. Only seven timing measurements (Rise, Fall, Frequency, Period,
Prop Delay, Cross, and Width) can be taken as hardware measurements.
Duty Cycle and Phase are software measurements; Jitter, Signal to Noise
Ratio, and Noise are statistical measurements. For example, the Rise mea
surement can be taken as a software measurement, a hardware measure
ment, or a statistical measurement. The RMS measurement is not a timing
measurement and cannot be taken as a hardware measurement.
You cannot take measurements in different modes on the same trace. You
can, however, create two or three identical traces and take measurements in
different modes on each. You can display only the measurements for the
selected trace at any one time.
Frequency Domain Measurements
The frequency domain measurements Spectral Freq, Spectral Mag, and
THD may be taken on FFT magnitude waveforms only. These selectors are
available on the Measurements pop up menu only when an FFT magnitude
waveform is selected and only in the Software Mode.
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11801C User Manual