UnderstandingOscilloscope Functions
TDS1000/2000-Series Digital Oscilloscope User Manual 21
Oscilloscope modelswith 60 MHz or 100 MHz bandwidth sampleat
rates up to 1 GS/s. Modelswith 200 MHz bandwidth sample at rates
up to 2 GS/s. In bothcases, these maximum sample rates are at least
ten times the bandwidth.These high sample rates help reduce the
possibility of aliasing.
There are several ways to check for al iasing:
HTurn the SEC/DIV knob to change the horizontal scal e. If the
shape of the waveform changes drasticall y, you may have
aliasing.
HSelect the Peak Detect acquisitionmode (described on page 17).
This mode samples the highe st and lowest values so that the
oscilloscope can detect fastersignals. If the shape of the
waveform changes drastically, you may have alia sing.
HIf the trigger frequency is faster than t he display information, you
may have aliasing or a waveform that crosses the trigger level
multiple times. Examining the waveform should allow identify-
ing whether the shape of the signal is going to allow a single
trigger crossingper cycle at the selected trigger level. If multiple
triggers are likely tooccur, select a trigger level that will generate
only a single trigger per cycle. Ifthe trigger frequency is still
faster than the display indicates,you may have aliasing.
If the trigger frequency i s slower,thi s test is not useful.
HIf the signal you are viewing is also the trigger source, use the
graticule or the cursorsto estimate the frequency of the displayed
waveform. Compare this to the Trigger Frequenc y readout in the
lower right corner of the screen. If they di fferby a large amount,
you may have aliasing.