Reflection Distortion
Electrical wave reflections propagate backward along PCB conductors whenever high speed signals encounter impedance discontinuities along their routing paths. Signal integrity characterization isolates transmission line reflections during time-domain reflectometry and high speed functional testing. This electrical phenomenon excludes low frequency voltage drops caused by direct current trace resistance.
Impedance Boundary
High speed digital signals propagate along trace networks as electromagnetic waves governed by characteristic line impedance. When an advancing signal edge reaches a boundary like a via transition, connector pin or mismatched termination resistor, transmission line reflections generate reverse-traveling voltage waves. These reflected waves superimpose onto incoming signal waveforms, producing ringing, voltage overshoot and undershoot at receiving component pads.
Extreme overshoot breaks down receiver input protection diodes, while undershoot induces false logic switching events. Signal integrity engineers place series or parallel termination resistors near trace ends to match driver or load impedance to the trace characteristic value. Time-domain reflectometers analyze reflection timing and amplitude to locate specific physical layout discontinuities along the signal route.
Wave Interruption
Mismatched impedance boundaries distort high speed logic waveforms and cause false switching. Controlled impedance layout and proper termination cancel reverse wave reflections. TDR measurements verify trace impedance consistency along full transmission paths.
