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Histograms and the
database
Histogram Commands
The HISTogram commands and queries control the histogram features.
A histogram is a probability distribution that shows the distribution of
acquired data within a user-definable histogram window.
You can display the histogram either vertically, for voltage
measurements, or horizontally, for timing measurements.
The most common use for histograms is measuring and characterizing
noise or jitter on displayed waveforms. Noise is measured by sizing the
histogram window to a narrow portion of time and observing a veritcal
histogram that measures the noise on a waveform. Jitter is measured by
sizing the histogram window to a narrow portion of voltage and observing
a horizontal histogram that measures the jitter on an edge.
These HISTogram commands and queries are implemented in the
Infiniium Oscilloscopes:
• AXIS
• MODE
• SCALe:SIZE
• WINDow:DEFault
• WINDow:SOURce
• WINDow:X1Position|LLIMit
• WINDow:X2Position|RLIMit
• WINDow:Y1Position|BLIMit
• WINDow:Y2Position|TLIMit
The histograms, mask testing, and color grade persistence use a specific
database that uses a different memory area from the waveform record
for each channel. When any of these features are turned on, the
oscilloscope starts building the database. The database is the size of the
graticule area. Behind each pixel is a 21-bit counter that is incremented
each time data from a channel or function hits a pixel. The maximum
count (saturation) for each counter is 2,097,151. You can use the
DISPlay:CGRade:LEVels command to see if any of the counters are close
to saturation.
18-2
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