Making ripple measurements has traditionally been using an oscilloscope. For a number of technical reasons, an oscilloscope, in general, is not necessarily the best choice for measuring ripple. These include relatively poor sensitivity, poor signal-to-noise performance (SNR), low resolution (generally 8 bits), and insufficient bandwidth. Bandwidth is generally reduced for low amplitude AC coupled signals.
There are several common issues. The first issue occurs when we try to measure ripple with a 1X AC coupled scope probe. A typical 1X scope probe only provides a bandwidth of 8-10MHz, while an uncompensated probe can show peaking at higher frequencies. Second, many scopes reduce the available bandwidth when used at the most sensitive settings or when AC coupled is enabled. Scopes often have a higher noise floor when set to high input impedance mode. Fig. 1 shows the typical frequency response of a 1X/10X scope probe in both the 1X and 10X positions.