LeCroy DDA-3000A, Руководство оператора

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WM-OM-E Rev I
There are additional considerations for each of these choices.
If you choose to analyze a part of a single Read Gate cycle, it is important that it include the VCO
Synch signal. Because it will be difficult to set up a reference signal if it is less than a single Read
Gate cycle, it is recommended that this not be done with either the Analog Compare or Channel
Emulation methods.
If you want to analyze a single Read Gate cycle, the easiest approach is to use the Read Gate
signal and, if necessary, the Analyze Region cursors, to determine which section is analyzed. If you
are using Channel Emulation or Analog Compare, you must make sure that the reference signal is
the same length (see the following Selecting the Reference Waveform).
If you wish to analyze multiple Read Gate cycles, the setup is the same as for a single Read Gate
cycle. The Read Gate signal and, if necessary, the Analyze Region cursors are used to determine
which sections are analyzed. If you are using Channel Emulation or Analog Compare, you need to
ensure that the reference signal is of similar makeup.
Except for Analog Compare, there are limits as to how much data the channel analysis methods
can analyze at the same time:
•
Channel Emulation without a reference saves ML sample results for up to 20,000 bits,
which are used to draw the ML sample (+) markers.
•
Channel Emulation with a reference saves up to 20,000 bits as its reference, while
also saving ML sample results; there can be up to 250 separate Read Gate true
sections in the data analyzed by Channel Emulation with reference.
•
Analog Compare can handle one block of data of any length up to the maximum that
can be acquired and stored by the DDA. It is the most computationally intensive error
find method, so its use on maximum length waveforms will not be typical. Another
indirect constraint on waveform size arises if Read Gate is used. If the source of Read
Gate is set to something other than NONE, Read Gate will break the data into multiple
blocks. In that case, there is a requirement that the start of each block, relative to the
first block in the reference and the acquisition, be the same within the DDA’s
realignment window of about 12 bit cells.
Selecting the Reference Waveform
The Analog Compare and Channel Emulation with reference signal channel analysis methods
compare the captured head signal to a stored reference head signal. For these methods, the
appropriate menus will only appear after a head signal has been selected.
The stored reference should be acquired in the same manner (same time/div, sample rate, trigger
position, etc.) and with the same timing as the acquisitions to which it is to be compared. It is not
possible to compare a reference having only one sector to every sector in an acquisition containing
many; and a split sector cannot be compared with an unsplit or differently split sector.
Generally, it is best that the reference signal be from the same drive section as the one with which
it is to be compared. This will ensure that any splits that occur are in the same location. Another
reason for selecting the same drive section is to avoid scrambler problems. If a drive uses a
scrambler, two sections with the same logic data may have different head signals. Since Channel
Emulation with reference and Analog Compare both analyze the head signal, they may see