Which statement best describes a relaxation oscillator?

• A. It relies on a resonance in an LC tank to generate a sine wave
• B. It generates a waveform by charging and discharging a capacitor through a comparator or Schmitt trigger
• C. It uses a phase-locked loop to regulate frequency
• D. It produces a jitter-free sawtooth from a crystal oscillator

Answer: (D)

A relaxation oscillator relies on a capacitor being charged and discharged through a nonlinear switching element, typically a comparator or Schmitt trigger. The Schmitt trigger provides two distinct thresholds, so as the capacitor voltage rises it triggers the switch at the upper threshold, flipping the output and causing the capacitor to discharge until it hits the lower threshold, then the process repeats. This charging and discharging cycle sets the period, determined by the RC values and the trigger thresholds, and it produces a non-sinusoidal waveform (usually a square wave at the output with a ramping voltage on the capacitor). This is different from oscillators that rely on LC resonance to produce sine waves, PLL-based frequency regulation, or crystal-based ramp systems.