Agilent Technologies E8267D PSG manual Using Waveform Scaling, How DAC Over-Range Errors Occur

Basic Digital Operation

Using Waveform Scaling

11.Press Waveform Statistics > CCDF Plot and observe the waveform’s curve. Notice the reduction in peak- to- average power, relative to the previous plot, after applying clipping.

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.

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