An investigation on oscilloscope input mismatch

The input mismatch of oscilloscope is investigated through measurement of the complex input reflection coefficient. Five models of real time digital storage oscilloscopes from four different manufacturers and having different bandwidths have been selected in order to identify the possible relevant peculiari-ties. Oscilloscope input reflection coefficient linearity, and dependence of mismatch on volt per division setting have been assessed. The measured complex reflection coefficient is here used to predict the electrostatic discharge waveform distortion due to oscilloscope mismatch. An analytical formula is also derived providing an upper limit of the measurement error of the impulse waveform caused by mismatch, useful for measurement uncertainty calculation.