PHY
Beginner
The part of a chip that turns digital data into the actual electrical signals sent over a wire, and back.
Novice
The physical-layer block of an interface such as PCIe, USB, Ethernet or DDR memory: the analog circuits that drive and receive the electrical signals on the wires, recover their timing and calibrate the link. It comes as finished layout for one manufacturing process.
Expert
Hard IP with its own power supplies, electrostatic-discharge protection and package-pin requirements. It sits at the die edge, so the number and type of PHYs constrain the chip’s shape, the package and the floorplan from the spec stage onward.