Datasheet

www.tektronix.com/power 3
Power Supply Measurement and Analysis with Bench Oscilloscopes
Oscilloscope Acquisition Modes
The oscilloscopes acquisition modes control how electrical
signals are sampled, processed, and displayed. The resulting
waveform points are digital values that are stored in memory
and displayed to construct the waveform. Most oscilloscopes
support different acquisition modes, and the acquisition mode
chosen may affect the accuracy of power measurements. It’s
important to understand how acquisition modes function and
the affect they will have on the waveform and ensuing power
measurements.
Every oscilloscope offers Sample Mode, which is the simplest
acquisition mode. As depicted in Figure 2, the oscilloscope
creates a waveform point by saving one sample point during
each waveform interval (waveform intervals are shown as
1, 2, 3, and 4 in thegure). Sample mode is suggested for
measurements on non-repetitive signals that are acquired over
multiple acquisitions such as ripple and noise analysis.
Another acquisition mode offered by most oscilloscope
manufacturers is Average Mode. In Average Mode, the
oscilloscope saves one sample point during each waveform
interval as in sample mode. However, in Average Mode,
corresponding waveform points from consecutive acquisitions
are then averaged together to produce thenal displayed
waveform as depicted in Figure 3. Average Mode reduces noise,
but requires a repetitive signal. Average Mode is especially useful
when performing harmonics analysis or power quality analysis
measurements such as true power, reactive power and apparent
power.
Tektronix also offers Hi Res Mode. In this mode, multiple
consecutive samples taken within one waveform interval are
averaged together to produce one waveform point from a single
acquisition as shown in Figure 4. The result is a decrease in
bandwidth and therefore noise, and an improvement in vertical
resolution for low-speed signals. Hi Res is especially useful for
conducting modulation analysis when powering up a supply and
acquiring data in a single acquisition. Hi Res may improve the
accuracy of measurements such as switching loss, which are
based on mathematically calculated values like instantaneous
power.
Figure 2. Sample Mode.
Figure 3. Average Mode.
Figure 4. Hi Res Mode.
1 2 3 4 1 2 3 4
Sample Mode
1 2 3 4 1 2 3 4
Sample Mode
1 2 3 4 1 2 3 4
Sample Mode