After many lengthy Spice simulations and some design tweaking, you're finally comfortable enough with your pc-board (PCB) design to build a prototype. Once it's built, you'll want to put the prototype on the lab bench and get it up and running. You'll typically use standalone or modular test instrumentation to take some measurements of operating characteristics to compare them to the simulation results. And this is where things can get very interesting.
Very often, those measurements and simulations don't correlate very well. Somewhere in the transition from a software-centric design environment to a hardware-centric, physical-measurement-based design environment, things can go awry. Spice models, detailed as they might be, reflect only an idealized design environment and often fail to account for realworld effects on circuit operation. This can cause a lengthy and very expensive iterative cycle of prototyping that continues until those unexpected real-world effects are accounted for.
Improving the process of circuit simulation is, to some extent, a matter of blurring the lines between design, characterization, and validation by improving the connectivity between design and measurement tools. Closing the design-tovalidation loop makes for less iteration by identifying discrepancies between your design (as simulated) and the prototype.