Buffering a Victim Net

A buffer increases the victim's signal strength and breaks the net into shorter segments, making the victim more tolerant of the coupled signal from the aggressor.

KEY Buffering boosts victim strength and shortens the net, improving crosstalk tolerance.

The SSO File

• SSO (Simultaneously Switching Outputs) refers to a number of IO buffers switching at the same time in the same direction. This generates noise on the power and ground lines because of the large di/dt and the parasitic inductance of the bonding wires on the IO power/ground cells.
• SSN is the noise produced by those simultaneously switching buffers; it shifts the voltage of the power/ground nodes, the well-known ground-bounce effect. It is measured at a quiet output held at a stable 0 or 1 while all other outputs switch together - the disturbance at that quiet node is called Quiet Output Switching (QOS), and the QOS of Vil is taken as the maximum tolerable noise.
• DI is the maximum number of copies of a given IO cell that can switch high-to-low together, with one ground cell, without pushing a quiet 0 output above Vil; the QOS of Vil is used as the criterion because a 1 has more noise margin than a 0. DF (Drive Factor) measures how much a given output buffer contributes to SSN on the power/ground rail; it is proportional to di/dt, and DF = 1/DI.

KEY SSO data quantifies ground-bounce noise from many IO buffers switching together, using QOS, DI and DF metrics.

Crosstalk

Crosstalk is interference where the switching of a signal on one net disturbs a neighbouring net through cross-coupling capacitance. It can push a path into a setup or hold violation.