A Reflection on a transmission line is an echo. A portion of the signal power (V&I) transmitted down the line goes into the load, & a portion is reflected. Reflections are prevented if the load & the line have the same impedance. Reflections are observed when impedance discontinuities exist in the transmission line. The reflection discontinuities are:
1. Lack of termination
2. Improperly matched termination circuits.
3. Change in trace width
4. Vias between routing layers
5. T-tubs, branched or bifurcated traces
6. Changes in impedance of the trace
7. Varying load and logic families
8. Connector transitions
9. Large power plane discontinuities.