When measuring a circuit or device with our network analyzers, engineers generally inject a signal and believe that the measured results reflect that of a small?signal AC measurement. Many of us have been taught to keep the signals “very small”. This raises the questions, “how small is very small” and “is this an issue with my network analyzer”?
SPICE based circuit simulators use partial derivatives to perform small?signal analysis, and therefore, are not sensitive to the signal level; regardless of the AC magnitude the results are linearized and scaled. So how big can an injected signal be before it significantly impacts a measurement? Let’s investigate the answer via a simple test.