Keysight 4000 X-Series, Руководство по продвинутой подготовке

Страница: 27 / 170

Oscilloscope Familiarization Labs
2
4000 X-Series Oscilloscopes Advanced Training Guide 27
18
Set channel-1’s offset to approximately 1.00 V in order to center the waveform
on-screen.
19
Push the trigger level knob to set the trigger level at approximately 50% .
20
Set the timebase to 20.0 µs/div . At this timebase setting there will be many
cycles of the clock signal on-screen, which is typically required when
performing a precision FFT math function.
21
Press the
[Math]
front panel key; then press the Operator softkey.
22
Select the FFT math function. Select the softkey Span and set to 100 MHz; then
set Center to 50 MHz.
You should now see a display similar to Figure 12 . The scope is now displaying
both a time domain waveform (Voltage versus Time) as well as a frequency domain
waveform (Power in units of dB versus Frequency). An FFT math function breaks
signals down into their individual sine wave frequency components. All electrical
signals, including digital signals, are composed of multiple sine waves of different
frequencies. An ideal clock signal that has a 50% duty cycle should consist of a
fundamental sine wave frequency component (signal’s repetitive frequency), plus
its odd harmonics (3rd, 5th, 7th, etc.). Note that non-ideal square waves will also
include lower-level even harmonics. Let’s now verify the frequencies of the
fundamental and odd harmonics.
Figure 12 Performing an FFT math function on a repetitive digital clock.