
Chapter 3 107
Basic Digital Operation
Understanding Waveform Clipping
How Clipping Reduces Peak-to-Average Power
You can reduce peak-to-average power, and consequently spectral regrowth, by clipping the
waveform to a selected percentage of its peak power. The ESG signal generator provides two
different methods of clipping: circular and rectangular.
During circular clipping, clipping is applied to the combined I and Q RF waveform (|I + jQ|).
Notice in Figure 3-19 that the clipping level is constant for all phases of the vector
representation and appears as a circle. During rectangular clipping, clipping is applied to the
I and Q waveforms separately (|I|, |Q|). Notice in Figure 3-20 on page 108 that the clipping
level is different for I and Q; therefore, it appears as a rectangle in the vector representation.
With either method, the objective is to clip the waveform to a level that effectively reduces
spectral regrowth, but does not compromise the integrity of the signal. Figure 3-21 on
page 109 uses two complementary cumulative distribution plots to show the reduction in
peak-to-average power that occurs after applying circular clipping to an RF waveform.
The lower you set the clipping value, the lower the peak power that is passed (or the more the
signal is clipped). Often, the peaks can be clipped successfully without substantially
interfering with the rest of the waveform. Data that might be lost in the clipping process is
salvaged because of the error correction inherent in the coded systems. If you clip too much of
the waveform, however, lost data is irrecoverable. You may have to try several clipping
settings to find a percentage that works well.
Figure 3-19 Circular Clipping
Kommentare zu diesen Handbüchern