Crosstalk is a phenomenon associated with the disturbance of signals across interconnects adjacent to each other. One interconnect may be transferring a signal as an adjacent interconnect may also be transferring a signal. If data within both signals change differently, coupling capacitance is created, delaying the transmission of data in a greater manner.
Three avoidance mechanisms were devised and created to mitigate the effects of coupling capacitance between adjacent interconnects.
- FOC: Forbidden Overlap Coding (FOC) is a crosstalk avoidance coding scheme that removes the common notion of “Up-Down-Up” and “Down-Up-Down” transitions. If the encoded word, or coded interconnect signal, has a “101” pattern at a bit position, the other code words cannot have the opposite pattern at the same bit position of “010”. This reduces crosstalk delay from (1 + 4λ)T to (1 + 3λ)T.
- FPC: Forbidden Pattern Coding (FPC) is a crosstalk avoidance coding scheme that does not allow “101” or “010” crosstalk. Transitioning to one of these code words at any position would give the highest amount of coupling capacitance since the signal is switching in the opposite direction the one adjacent to it is, causing the worst-case delay for signal data.
- FTC: Forbidden Transition Coding (FTC) is a crosstalk avoidance coding scheme that does not allow “01” and “10” to exist within coded words at the same bit position. Transitioning to one of these code words at the same position would cause a delay similar to that of the FPC.