Agilent Technologies E8267C PSG, E8247C PSG CW manual How Clipping Reduces Peak-to-Average Power

Dual Arbitrary Waveform Generator

Using 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 PSG vector signal generator provides two different methods of clipping: circular and rectangular.

During circular clipping, clipping is applied to the combined I and Q waveform (I + jQ). Notice in Figure 5-15that 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 5-16 on page 117 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 5-17 on page 118 uses two complementary cumulative distribution plots to show the reduction in peak-to-average power that occurs after applying circular clipping to a 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 5-15 Circular Clipping

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