LeCroy DDA 7 Zi series, Operator'S Manual

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WavePro 7Zi
459
WP700Zi-OM-E-RevA
3. Touch inside the Position Segment data entry field and enter a value from 1 to 999 using the pop-up
numeric keypad.
4. Touch inside the Position Byte field and enter a value from -50 to 50,000 using the pop-up numeric
keypad.
5. If you want to increase or decrease your horizontal or vertical zoom in small increments, touch the Var.
checkbox in the right-hand dialog to enable variable zooming. Now with each touch of the zoom control
buttons , the degree of magnification will change by a small increment.
To zoom in or out in large standard increments with each touch of the zoom control buttons, leave the Var.
checkbox unchecked.
To set exact horizontal or vertical zoom factors, touch inside the Horizontal Scale/div data entry field and
enter a time-per-div value, using the pop-up numeric keypad. Then touch inside the Vertical Scale/div field
and enter a voltage value.
6. To reset the zoom to x1 magnification, touch Reset Zoom in the dialog or press the front panel zoom
button .
Channel Analysis Concepts
The purpose of Channel Analysis is to find signal quality problems in the head signal. Thus, both methods used
by the DDA (Channel Emulation and Analog Compare) require that you first specify the DDA channel or memory
on which the head signal is to be carried.
The instrument utilizes the head signal and, optionally, the Read Gate and the Analyze Region cursors to
determine which part of the head signal will be analyzed. What follows is an explanation of how the instrument
does this and the manner in which it processes the head signal.
The following figure shows the fields of the head signal and their relationship to Read Gate.
Head Signal Fields and Read Gate
In a normally operating disk drive, every time Read Gate goes true (at the beginning of every segment to be read)
there must be a repetitive signal called the VCO Synch (voltage-controlled oscillator). It is needed to adjust the
phase of the PLL (phase locked loop), which generates the sampling clock, and to adjust the AGC (automatic
gain control).
The DDA will try to identify the VCO Synch signal in a similar fashion in order to perform channel emulation. In
order to identify VCO Synch, you will need to provide a Read Gate signal or to set the Analyze Region cursors
(see
Selecting the Waveform Section to be Analyzed ). After the DDA analyzes the VCO Synch signal, it is ready
to analyze the data field for problems. Since the data field generally does not start immediately after the end of
the VCO Synch field, the DDA needs to know where the data field starts. You must specify the number of bytes
between the VCO Synch field and the data field. The DDA can then determine the location of the first byte of data.