Ethernet is simply the wiring and low level communication standards in local area network. Under these specifications, computers can be connected use standardized cable, jack, and communication hardware at ease.


Ethernet: it a computer communication standards interconnecting computers within a local area network commonly found in home and offices. Standardized as IEEE 802.3

Local Area Network (LAN): It's a simple computer network that connects local computers together with network coverage limited to home, school, offices, etc. Intranet is a good example of using a full LAN for a large business office.

Media Access Controller (MAC): It's part of the data link layer of the communication OSI model that controls the data flow and data multiplexing for the physical layer transmission.

Physical Layer (PHY): It's the lowest layer of communication OSI model that generate and sends electrical signal down to the wire based on the data control from MAC.

MII (Media independent Interface): It's a digital interface that connects between a MAC block and a PHY hardware.

RGMMI (Reduced Gigabyte Media independent Interface): It's a reduction of pin count version of GMMI (half of that of GMII interface) interface between a MACK block and a PHY hardware.

Media depend Interface (MDI): It's a interface that describes Ethernet link over twisted pair for PC, servers, and routers.


    • Speed
      • 100BaseT (100Mbit/s)
      • 1000BaseT (1 Gbit/s)
    • Medium
      • Wired twisted pair cable
        • 2 pairs required for 100BaseT
        • 4 pairs required for 1000Base T
      • Cable Type
        • 100/1000 Base T uses CAT5e grade cable.
    • Connector
      • RJ45 is the wired Ethernet connector (8P8C modular connector)

Example Design

Objective: Designing a Ethernet jack and its connection to the main processor

A typical system on chip has integrated Ethernet peripheral, which includes a media access controller block or and a physical layer hardware to interface with the wired transmission MDI interface from RJ45 Ethernet jack.

100 Base T Ethernet Design

100BaseT design

RJ45 signal directly connect to application processor.

1000Base T design (i.e gigbit internet)

1000 Base T Ethernet Design

A dedicated Ethernet PHY transceiver chip between RJ45 jack and application processor via RGMII interface.

Ethernet Magnetic is needed to provide signal isolation and noise filtering between electronic product and Ethernet networking devices such as router and switch..

    • A typical Magnetic contains common choke filter and a transformer.
        • MDI interface are high speed differential signals (aka. AC signals) that can be transferred through a transformer.
        • Transformer contains an magnetic core which saturates itself when there an incoming high surge current; this saturation property of the core provides electrical isolation.
        • Common mode choke provides high impedance to common mode signal but low impedance to differential signals (i.e ethernet MDI signals), hence signal is can be transmitted through due to low impedance but common mode noise is heavily attenuated by high impedance.


Summary & Conclusion

  • Ethernet is a computer networking standard
  • RJ45 is the Ethernet connector
  • PHY chip is often needed for higher data rate 1000 Base T Ethernet between RJ45 and application processor.
  • Ethernet magnetics contains a isolation piece (a transformer) and filter (Common mode choke)

Wired Ethernet design enables stable connectivity and is designed based on speed requirements. As an electronic system engineer, selecting right magnetics and PHY chip with right MII interface enables correct Ethernet design.