PLL with programmable jitter for loopback serdes testing and the like

摘要

In one embodiment of the invention, a phase-locked loop (PLL) can be programmably controlled to add jitter to its PLL output clock. Such a PLL can be used to programmably inject jitter into the outgoing serial data signal generated by a serializer/de-serializer (serdes) that can be operated in an internal loopback mode, in which the outgoing serial data signal is internally looped back from the transmitter side of the serdes to the serdes receiver side. Jitter logic associated with the PLL can be operated in a register-based mode that does not rely on any externally generated jitter clock. Such register-based processing enables effective (1) internal loopback testing of unpackaged devices at the wafer stage as well as package devices at the package stage and (2) external loopback testing at the system level.