What does the bandwidth of an oscilloscope determine?

• A. The maximum voltage range it can measure.
• B. The display refresh rate.
• C. The highest frequency that can be faithfully reproduced.
• D. The input impedance.

Answer: (C)

Bandwidth sets how high in frequency the oscilloscope can pass the signal without significant attenuation. In other words, it defines the highest frequency at which the instrument can faithfully reproduce the waveform. The front-end circuitry, cables, and probes all have a frequency response that rolls off as frequency increases, so components above the bandwidth are damped and shifted in phase. That attenuation and phase distortion mean sharp edges and fast transitions get blurred, especially for signals with many high-frequency components.

Practically, to capture a signal accurately you want the scope’s bandwidth well above the signal’s highest frequency components; a common rule is to use a bandwidth several times higher than that frequency to preserve waveform shape. For example, a 100 MHz signal benefits from a scope with a bandwidth well above 100 MHz to avoid noticeable attenuation and distortion of the waveform.

The other specs don’t determine this capability: the maximum voltage range relates to vertical sensitivity, not frequency response; the display refresh rate affects how often the screen updates, not the scope’s ability to pass high frequencies; and input impedance describes the load the scope presents to the circuit, not how fast it can respond to changes.