What Is an Ethernet PHY?
An Ethernet PHY is a special interface chip that converts a device's digital network data into a physical signal that can travel over the Ethernet cable (and vice versa). It's the "physical layer" element of the network.
The MAC and PHY Relationship
Ethernet has two layers: the MAC (manages the data frames, usually inside the processor) and the PHY (converts these frames into a cable-suitable analog signal). The PHY is the bridge between the MAC and the cable.
How Does It Work?
The PHY encodes the digital data and converts it into differential signals and sends them over twisted-pair cables. The PHY on the other side converts it back to digital; the speed negotiation (auto-negotiation) is done automatically.
| Layer | Job |
|---|---|
| MAC | Frame/address management |
| PHY | Physical signal conversion |
| MII/RMII | MAC-PHY interface |
Magnetics and Connector
Between the PHY and the RJ45 connector there's a magnetics (transformer) module for isolation and noise suppression. This protects the device from line voltage differences.
Where Is It Used?
Network cards, routers, switches, IP cameras, industrial controllers and Ethernet-capable embedded devices.
Speed and Auto-Negotiation
Ethernet PHYs support different speeds like 10/100/1000 Mbps. When two devices connect, an "auto-negotiation" process runs that automatically determines the common highest speed and duplex mode. This lets devices of different capabilities communicate compatibly.
Common Mistakes
- Skipping the magnetics: without the isolation magnetics the PHY can be damaged.
- Impedance: the differential lines must be routed to 100Ω.
- Clock/strap: the PHY's startup settings (strap pins) must be set correctly.
Frequently Asked Questions
What's the difference between MAC and PHY?+
What are MII/RMII?+
Search parts related to "What Is an Ethernet PHY?"
Find the right part by comparing price, stock and distributors.