Trace Reflections
Reflections: Signal reflections on the trace are caused by a
number of conditions. Avoid discontinuities on PWB traces; changes in the
impedance of the trace will cause reflections. Termination of traces will
reduce or eliminate reflections from the 'far-end' IC; see Trace
Termination Schemes for the primary reason. Additions causes
include:
Sharp bends; the cross-sectional area of the trace
increases at the bend lowering Zo.
Vias; A vertical run between
board layers is an uncontrolled impedance.
Layer changes; Moving
from an outside layer {stripline} to an inside layer {microstrip}. Avoid
stubs on the signal lines, stubs are really traces that require a
termination resistor.
Additional Digital Logic Pitfalls.
