Keysight E8663D, Руководство пользователя

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140 Keysight E8357D/67D & E8663D PSG User’s Guide
Basic Digital Operation
Using Waveform Scaling
Using Waveform Scaling
Waveform scaling is used to eliminate DAC over–range errors. The PSG
provides two methods of waveform scaling. You can perform runtime scaling,
which enables you to make real–time scaling adjustments of a currently
playing waveform, or you can permanently scale a non–playing waveform file
residing in volatile memory. This section describes how DAC over–range errors
occur and how you can use waveform scaling to eliminate these errors
effectively.
The scaling feature is available only with the Dual ARB mode.
How DAC Over–Range Errors Occur
The PSG utilizes an interpolator filter in the conversion of the digital I and Q
baseband waveforms into analog waveforms. The clock rate of the interpolator
is four times that of the baseband clock. The interpolator therefore calculates
sample points between the incoming baseband samples to equal the faster
clock rate and smooth out the waveform, giving it a more curve–like
appearance (see Figure 3-17 ).
Figure 3-17 Waveform Interpolation
The interpolation filters in the DAC’s have overshoot. If a baseband waveform
has a fast–rising edge, the interpolator filter’s overshoot or frequency response
becomes a component of the interpolated baseband waveform. This response
causes a ripple or ringing effect at the peak of the rising edge. If this ripple
exceeds (or overshoots) the upper limit of the DAC’s range, the interpolator
calculates erroneous sample points and is unable to replicate the true form of
the ripple (see Figure 3-18 ). As a result, the PSG reports a DAC over–range
error.