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V i d e o
S i g n a l
During a sweep, only a specified amount of time is available for writing data into each of the 1001 trace memory
addresses. In two of these time periods, the positive and negative peak detectors obtain the maximum and
minimum video signal excursions, respectively, and store these values in ahernate trace memory addresses. This
technique allows a graphic presentation of noise on the CRT display.
Normal Mode
In normal mode, a detection algorithm selectively chooses between the positive and negative peak values to be
displayed. The choice is made dependent upon the type of video signal present.
Data from the positive peak detector (signal maximums) will alway be displayed in the odd-addressed trace
memories (1, 3, . . . 1001). If, within the time period following the storage of a value in an odd-addressed memory,
there is no change in video signal level, the positive peak detector value will also be stored in the even address. In
other words, the even-addressed memory will also contain positive peak detection data if the signal during that
time period is monotonic. Negative peak detector data (video signal minimum) will be stored in the even-
addressed trace memory if the signal has a point of inflection during the time period.
Normal mode is selected with instrument preset.
Sample Mode
In the sample mode, the instantaneous signal value of the final analog-to-digital conversion for the time period is
placed in memory. (As sweeptime increases, many analog-to-digital conversions occur in each time period, but
only the final, single value can be stored.)
Sample mode is selected automatically for video averaging and noise level.
Positive and Negative Peak Modes
Positive and negative peak modes store signal maximums and minimums, respectively, in all trace memories.
98 Manual Operation
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