A
PHY, an abbreviation for
physical layer, is an
electronic circuit, usually implemented as an
integrated circuit, required to implement physical layer functions of the
OSI model in a
network interface controller. A PHY connects a
link layer device (often called MAC as an acronym for
medium access control) to a physical medium such as an
optical fiber or
copper cable. A PHY device typically includes both
physical coding sublayer (PCS) and
physical medium dependent (PMD) layer functionality.
-PHY may also be used as a suffix to form a short name referencing a specific physical layer protocol, for example
M-PHY. Modular transceivers for
fiber-optic communication (like the
SFP family) complement a PHY chip and form the
PMD sublayer.
Ethernet physical transceiver KS8721CL – 3.3 V single power supply 10/100BASE-TX/FX MII physical layer transceiver The
Ethernet PHY is a component that operates at the physical layer of the
OSI network model. It implements the physical layer portion of the Ethernet. Its purpose is to provide analog signal physical access to the link. It is usually interfaced with a
media-independent interface (MII) to a MAC chip in a
microcontroller or another system that takes care of the higher-layer functions. More specifically, the Ethernet PHY is a chip that implements the hardware send and receive function of Ethernet
frames; it interfaces between the analog domain of
Ethernet's line modulation and the digital domain of link-layer
packet signaling. The PHY usually does not handle MAC addressing, as that is the
link layer's job. Similarly,
wake-on-LAN and
boot ROM functionality is implemented in the
network interface card (NIC), which may have PHY, MAC, and other functionality integrated into one chip or as separate chips. Common Ethernet interfaces include fiber or two to four copper pairs for data communication. However, there now exists a new interface, called Single Pair Ethernet (SPE), which is able to utilize a single pair of copper wires while still communicating at the intended speeds.
Texas Instruments DP83TD510E is an example of a PHY which uses SPE. Examples include the
Microsemi SimpliPHY and SynchroPHY VSC82xx/84xx/85xx/86xx family,
Marvell Alaska 88E1310/88E1310S/88E1318/88E1318S Gigabit Ethernet transceivers, Texas Instruments DP838xx family and offerings from Intel and ICS.
Other applications •
Wireless LAN or
Wi-Fi: The PHY portion consists of the RF, mixed-signal and analog portions, which are often called transceivers, and the digital baseband portion that uses
digital signal processor (DSP) and communication algorithm processing, including
channel codes. It is common that these PHY portions are integrated with the
medium access control (MAC) layer in
system-on-a-chip (SOC) implementations. Similar wireless applications include
3G/
4G/
LTE/
5G,
WiMAX and
UWB. •
Universal Serial Bus (USB): A PHY chip is integrated into most USB controllers in hosts or
embedded systems and provides the bridge between the digital and modulated parts of the interface. • IrDA: The
Infrared Data Association's (IrDA) specification includes an IrPHY specification for the physical layer of the data transport. •
Serial ATA (SATA): Serial ATA controllers use a PHY. •
PCI Express (PCIe): PCI Express controllers use a PHY. == Technologies ==