Which of the following is characteristic of a direct digital synthesizer (DDS)?
Extremely narrow tuning range
Relatively high-power output
Pure sine wave output
Variable output frequency with the stability of a crystal oscillator✓الإجابة الصحيحة
الشرح
A DDS builds its output numerically from a fixed reference clock, so the frequency is freely programmable while its accuracy and drift are those of the crystal reference. Because the waveform is synthesized in discrete steps the output carries spurious products, so it is not a pure sine wave.