A high speed Sample-Hold can extend the bandwidth of the analog inputs to 20 MHz. 

Below is the first prototype. It has 1st order passive or 2^nd order active reconstruction filters and AC / DC coupling.

          This Document explains how it works.
          This Schematic shows how it is built.

Here is the final version which operates from a 9 V battery.  A 10X input attenuator was added as
well as the 2^nd order filters and AC/DC coupling.