Chipset End of Life Notices and the Redesign Clock
A silicon end-of-life notice demands an immediate audit of last-time-buy volumes against redesign lead times to prevent production gaps during recertification.
Microstrip via Fence
Meaning
Physical isolation structure consisting of a row of grounded vertical interconnects placed alongside a high frequency transmission line. Using a microstrip via fence reduces the electromagnetic coupling between adjacent traces on a printed circuit board. This structure acts as a conductive wall that terminates the fringing fields before they can reach other sensitive parts of the circuit.
Crosstalk Suppression
Near field energy from a signal trace induces currents in neighboring lines through capacitive and inductive coupling. Grounded vias placed at regular intervals provide a low impedance path to the ground plane for these unwanted fields.
Signal Integrity
Containment of the field lines ensures that the characteristic impedance of the transmission line remains stable. The spacing between the vias must be less than one tenth of the wavelength to prevent the energy from leaking through the gaps. A well designed fence maintains the quality of the high speed data pulse by reducing reflections and timing jitter.
Geometric Constraint
Adding a row of vias requires extra space on the board layout and increases the complexity of the manufacturing process. The distance from the trace to the fence must be balanced to avoid shifting the impedance of the signal line. Proper placement prevents the fence from becoming a resonant structure that would otherwise radiate energy at specific frequencies.