Answer 6—A digital oscilloscope captures voltage waveforms into digital memory by performing an A/D conversion on the signals, usually with 8 to 10 bits of resolution. Sampling rates run from tens of megahertz to tens of gigahertz, and a typical unit will have anywhere from one to four channels. The memory does not tend to be particularly deep except in special applications.

A logic analyzer typically has many more channels (hundreds, in some cases) and much deeper memory than a digital oscilloscope, and all channels are sampled simultaneously. The deep memory allows a large amount of pretrigger information to be viewed, showing what led up to the trigger event. However, each channel is digitized by a 1-bit converter (a comparator) that simply decides whether the signal is “low” or “high,” whatever those terms mean in the particular logic family being used. A logic analyzer is useful for debugging complex digital systems and monitoring the values on processor busses, but it tells you nothing about the actual waveform of the signal.

Contributor: David Tweed