Keysight E8663D, Руководство пользователя

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Keysight E8357D/67D & E8663D PSG User’s Guide 133
Basic Digital Operation
Using Waveform Clipping
Using Waveform Clipping
Waveforms with high power peaks can cause intermodulation distortion, which
generates spectral regrowth (a condition that interferes with signals in
adjacent frequency bands). The clipping function enables you to reduce high
power peaks by clipping the I and Q data to a selected percentage of its
highest peak.
The clipping feature is available only with the Dual ARB mode.
How Power Peaks Develop
To understand how clipping reduces high power peaks, it is important to know
how the peaks develop as the signal is constructed.
I/Q waveforms can be the summation of multiple channels (see
Figure 3-10 ).
Whenever most or all of the individual channel waveforms simultaneously
contain a bit in the same state (high or low), an unusually high power peak
(negative or positive) occurs in the summed waveform. This does not happen
frequently because the high and low states of the bits on these channel
waveforms are random, which causes a canceling effect.
Figure 3-10 Multiple Channel Summing
The I and Q waveforms combine in the I/Q modulator to create an RF
waveform. The magnitude of the RF envelope is determined by the equation
, where the squaring of I and Q always results in a positive value.
As shown in Figure 3-11 , simultaneous positive and negative peaks in the I and
Q waveforms do not cancel each other, but combine to create an even greater
peak.