What waveform does a crystal-controlled oscillator typically produce?

A crystal-controlled oscillator is designed to produce a highly stable frequency output, which is primarily in the form of a sine wave. The reason for this is that crystal oscillators rely on the mechanical resonance of a vibrating crystal to generate an accurate frequency. This resonance tends to produce a pure sine wave because it reflects the natural oscillatory behavior of the crystal itself.

In applications, while it's common to see the output of a crystal oscillator represented in different forms such as square waves (in digital circuits) due to the function they serve in the system, the fundamental waveform generated directly by the crystal is indeed a sine wave. The inherent characteristics of a sine wave—smooth periodic oscillation and fundamental frequency—are crucial for fulfilling the requirements of high precision in timing and frequency control in electronic circuits.

Understanding this fundamental property of a crystal oscillator is essential for various applications in electronics, where precision timing is critical.