General exam question G7C05

WhyA direct digital synthesizer produces a variable output frequency with the stability of a crystal oscillator. A direct digital synthesizer generates its output by digitally stepping through a stored waveform table referenced to a single stable clock, so it can be tuned smoothly across a wide range of output frequencies while still inheriting that clock's crystal-level frequency stability, answer D. A DDS actually offers a wide tuning range, not an extremely narrow one, its raw output is relatively low power (needing amplification for most uses), and its output isn't a perfectly pure sine wave, it carries some quantization-related spurs, so A, B, and C are wrong.