What stage of an oscilloscope determines the maximum frequency response?

The vertical amplifier is crucial in determining the maximum frequency response of an oscilloscope because it is responsible for amplifying the input signal before it is displayed on the screen. The vertical amplifier's design and bandwidth directly influence how quickly it can respond to changes in the input signal's voltage.

When a signal is rapidly changing, such as a high-frequency waveform, the vertical amplifier must have a sufficient bandwidth to accurately reproduce the signal's characteristics without distortion or lag. If the amplifier's bandwidth is too narrow, it will fail to capture the peaks and troughs of the signal properly, leading to inaccurate representation on the oscilloscope.

Thus, the quality of the vertical amplifier is essential for the oscilloscope's ability to measure and display high-frequency signals accurately. In contrast, the trigger circuit is responsible for stabilizing the waveform display, the horizontal amplifier deals with timebase and sweep rate, and the signal processor handles functions like measurements and analysis, but none of these functions directly determines the frequency response as the vertical amplifier does.