Read this article online.

To reliably capture high-frequency signals and fast transient pulses, wide-bandwidth data-acquisition systems such as oscilloscopes and active probes require high-performance analog-front-end (AFE) signal chains.

These AFE signal chains must ensure a high signal-to-noise ratio, offer low noise and distortion, and deliver high dc precision. They also must present a high input impedance (Hi-Z) over a wide frequency range to the device under test. Texas Instruments’ BUF802, an open-loop unity-gain buffer with a JFET-input stage, can help you achieve these goals.