User`s manual

1-4
IM 701610-01E
Relationship between the Time Axis Setting, Sample Rate and Record Length
Changing the time axis causes corresponding changes in the sampling rate and the
acquisition record length. For more detailed information, see Appendix 1.
Relationship between Time Axis Setting and Sampling Mode
The sampling method (sampling mode) for an input signal changes according to the time axis
setting as described hereafter. But note that the time axis range over which this feature is actually
available will vary according to the maximum displayable record length, as shown in Appendix 1.
• Real-Time Sampling Mode
Changing the time axis causes a corresponding change in the sampling rate. The
maximum sampling rate is 200 MS/s (or 100 MS/s if the high-resolution mode is ON.).
The input signal is sampled sequentially, and data is stored in the acquisition memory.
In this mode, the waveform can only be displayed correctly at frequencies up to half the
sample rate, due to Nyquist’s theorem*. Sample rate is expressed in S/s (number of
samples per second). Thus, this mode is suitable for observation of a waveform which
fluctuates more slowly than the sample rate.
* If the sample rate is higher than the frequency of the input signal, high-frequency
components will be lost. In this case, a phenomenon in which high-frequency
components change to lower frequency components occurs, due to Nyquist’s theorem.
This phenomenon is called aliasing. Aliasing can be avoided by setting the acquisition
mode to envelope mode and acquiring the waveform.
Aliasing Signal Input Signal Sampling Point
• Repetitive Sampling Mode
To enable this mode, you must set the time axis so that the sampling rate is greater than
200 MS/s (high-resolution mode ON: 100 MS/s). Under this mode, the oscilloscope
produces a single waveform by taking samples over several periods of a repetitive signal,
so that the sampling rate appears higher than it actually is. An apparent sample rate of up
to 50 GS/s can be used.
Furthermore, even in the real-time sampling mode, if the sample rate exceeds 200 MS/s
(high-resolution mode ON: 100 MS/s) due to the time axis and the displayed record length
settings, the sampling mode automatically changes to repetitive sampling.
There are two repetitive sampling methods: sequential sampling, in which a signal is
sampled sequentially at a fixed interval, and random sampling, in which a signal is
sampled at random to produce a waveform. This instrument uses a random sampling
method which also enables observation of the waveform up to the trigger point.
Time Axis Setting and Roll Mode Display
If the time axis is set within a certain range (see Appendix 1), then the display will not be
updated by trigger anymore (update mode), but the mode will switch to roll mode when new
data is acquired. In roll mode, the oldest data is deleted, and the waveform shifts from right
to left on the screen. A waveform can be observed in the same way as it is recorded on a
pen recorder. This mode is useful when you are observing a signal which repeats or which
fluctuates slowly. This mode is also useful when you want to detect glitches (fast spikes on a
waveform) which occur intermittently.
* Rolling display also operates during single - start acquisition, although trigger occurrence
causes the waveform to stop.
1.2 Setting the Vertical and Horizontal Axes