Transceivers

Transceivers are special purpose integrated circuits that enable a microprocessor system to communicate via an interface standard over a wide variety of different protocols. Such protocols include serial networking interfaces like Ethernet, CAN bus and token ring. It can also incorporate peripheral interfaces like RS232, USB and firewire. Modern high-speed serial interfaces like SATA, PCIe, HDMI, Thunderbolt and SDI have special analog and clock circuitry to accommodate for the extremely high bit rates and long cable lengths. Transceivers can also be built into microprocessors and FPGAs to interface to other devices on board or over system backplanes.
Ethernet transceivers are also referred to as Ethernet PHYs. This relates to the physical layer of the open systems interconnection (OSI) seven-layer model. The PHY (physical) layer incorporates the control, timing, modulation, signal conditioning and interface conversions that enable interconnection of nodes on Ethernet cable. This includes cable and fiber, but variations exist to do similar networking over the wireless medium.
Transceivers perform physical signaling conversions from the standard logic or LVDS interfaces to higher voltage swings (for example RS232), low voltage differential transfer (USB) or other forms like differential current mode logic (CML). Physical mediums can introduce amplitude and phase distortions due to high-frequency roll-off, losses and other filtering effects. These can be accommodated for by the pre-distortion of signals in the transmitter and equalization in the receiver.
High-speed serial transceivers will incorporate phase locked loops (PLLs), voltage controlled oscillators (VCOs) and word synchronization algorithms that recover and reconstruct a data clock (reclocking). Special bit encoding can be used to ensure sufficient edge transitions for clock recovery, while limiting or eliminating any pattern dependent DC offsets that may eventuate by the data transfer (for example, Manchester Encoding).
Modern bus standards utilize serial channels in parallel to data transfer referred to as lanes or channels. High-speed logic muxes and demuxes take parallel words and chop them up into serialized data streams (serializers and deserializers). Transceivers are usually represented as a collection of subsystems. The physical medium attachment (PMA) module handles the analog interface. The physical coding sub-layer (PCS) is the encoding, data scrambling, alignment, serializing and deserializing subsystem. A clock management unit (CMU) contains a clock and data recovery block, PLL and VCO. Jitter is resolved through using FIFOs as jitter buffers and additional circuitry is incorporated for managing lanes in multi-transceiver interface connections.