AC And DC image
I assume you simply want a series of digital samples representing the dV/dt wave forms? Regardless of what you want to do with these samples the answer is an ADC. Depending on what you want to do with these samples, the ADC can be a discrete IC, a feature of a microcontroller or the sound card on your PC. You should prolly give a bit more detail about what you are trying to do. Ultimately the easiest answer is an oscilloscope, but I assume you have some purpose in mind that precludes this obvious answer.
Fish