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TDS 620A, 640A & 644A User Manual
3Ć151
Zoom
At times, you may want to expand or compress a waveform on the display
without changing the acquisition parameters. You can do that with the zoom
feature.
When you zoom in on a waveform on the display, you expand a portion of
the waveform. The digitizing oscilloscope may need to show more points for
that portion than it has acquired. If it needs to do this, it interpolates. The
instrument can interpolate in either of two ways: linear or sin(x)/x. (The
interpolation methods are described on page 2Ć20.)
When you zoom, the display redraws the waveforms using the interpolation
method you selected in the Display menu (linear interpolation or sin(x)/x). If
you selected sin(x)/x (the default), it may introduce some overshoot or
undershoot to the waveform edges. If that happens, change the interpolaĆ
tion method to linear, following the instructions on page 3Ć152.
To differentiate between the real and interpolated samples, set the display
style to Intensified Samples.
When you turn on the zoom feature, the vertical and horizontal scale and
vertical position knobs now control the displayed size and position of waveĆ
forms, allowing them to be expanded and repositioned on screen. They
cease to affect waveform acquisition, but you can alter acquisition by using
the corresponding menu items. Zoom mode does not change the way
horizontal position operates.
To use zoom, do the following steps:
1. Press ZOOM ➞ ON (side). The ZOOM frontĆpanel button should light
up.
2. Choose which waveforms to zoom by repeatedly pressing Horizontal
Lock (side).
H None Ċ only the waveform currently selected can be magnified and
positioned horizontally (Figure 3Ć81).
H Live Ċ all channels (including AUX channels for the TDS 620A) can
be magnified and positioned horizontally at the same time. (WaveĆ
forms displayed from an input channel are live; math and reference
waveforms are not live.)
H All Ċ all waveforms displayed (channels, math, and/or reference)
can be magnified and positioned horizontally at the same time.
Zoom and
Interpolation
Operation