Introduction to Ethernet


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.


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 magnetics is a component that is used to provide signal isolation and noise filtering between electronic products and Ethernet networking devices such as routers and switches. A typical Ethernet magnetic contains a common choke filter and a transformer.

The MDI interface, which is used to connect an electronic product to an Ethernet network, uses high-speed differential signals (also known as AC signals). These signals can be transferred through a transformer. The transformer contains a magnetic core that saturates when a high surge current flows through it. This saturation property of the core provides electrical isolation.

The common mode choke provides high impedance to common-mode signals, but low impedance to differential signals (such as Ethernet MDI signals). This means that the signal can be transmitted through the choke due to its low impedance, but common-mode noise is heavily attenuated by its high impedance.

A refreshers on engineering princples:

In summary, Ethernet magnetics provides signal isolation and noise filtering by using a transformer to transfer high-speed differential signals and a common mode choke to attenuate common-mode noise.


Q: What is Ethernet?

A: Ethernet is a computer networking standard that specifies how devices on a network can communicate with each other.

Q: What is RJ45?

A: RJ45 is the most common type of Ethernet connector. It is a 8-pin connector that is used to connect devices to an Ethernet network.

Q: What is a PHY chip?

A: A PHY chip is a physical layer interface chip that is used to connect an Ethernet device to an Ethernet network. PHY chips are responsible for converting data from the digital domain to the analog domain and vice versa.

Q: What is Ethernet magnetics?

A: Ethernet magnetics is a component that is used to isolate and filter the signals on an Ethernet network. Ethernet magnetics are typically composed of a transformer and a common mode choke.

Q: How is Ethernet used in wired networks?

A: Ethernet is used in wired networks to connect devices to each other. Ethernet networks are typically designed based on the speed requirements of the devices that are connected to the network.

Q: How do I select the right magnetics and PHY chip for my Ethernet design?

A: The right magnetics and PHY chip for your Ethernet design will depend on the speed requirements of your network and the type of devices that are connected to the network. You should consult with an electronic system engineer to select the right magnetics and PHY chip for your application.

Summary & Conclusion

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.