TI Tip: 2 Ways to Save Power with Low-Power Ethernet

“Why does Ethernet consume so much power?” is a question many people wonder about.

The rated active power of a 10/100Mbps Ethernet physical layer (PHY) transceiver ranges from 110mW to over 300mW, while a 10/100/1000Mbps Gigabit Ethernet PHY consumes 450mW to over 1,000mW of power. Often, the Ethernet PHY is one of the single most power-consuming components on a board and is a critical factor in evaluating the thermal budget of a closed system. There are various low-power modes that can be applied to Ethernet to reduce overall system power.


Then, is it possible to keep the system temperature low and reduce power costs? Let's take a look at two representative power saving techniques.

Energy Efficient Ethernet (EEE)

Energy-efficient Ethernet (EEE), defined in IEEE 802.3az, is a PHY and MAC (media access control) standard that eliminates standby signaling when channel usage is low. As shown in Figure 1, EEE implements a low-power mode in which the transmitter is disabled during 'quiet' times when there is no data to transmit, except for short refresh intervals. In this way, power is saved by eliminating the unnecessary continuous transmission of standby symbols through active links during quiet periods. The refresh interval ensures that the existence and timing of links within the PHY and between them remain valid.


Figure 1. EEE state flow

If there is data to transmit, the MAC signal to the PHY terminates the EEE state, making the EEE mode transparent to the upper layers. The PHY exits low-power mode and transmits a standby state code group to call the far-end device out of low-power mode. More details about EEE can be found in the application note “DP83822 Energy Efficient Ethernet IEEE 802.3az”.

Wake on Land (WoL)

Wake-on-LAN (WoL) saves power by keeping the Ethernet PHY active but selectively lowering the power of the system's backend elements (processors, microcontrollers, ASICs, or other components). These backend elements become active when the Ethernet PHY receives a specific 'magic' packet.

WoL is a technique that can reduce overall system power while keeping Ethernet transceivers active when the system has a properly defined signal commanding operation. Various methods for implementing WoL can be found in the application note “DP83822 Wake-On-LAN”. Figure 2 shows a magic pattern structure in which the Ethernet PHY monitors incoming packets before sending a drive signal.


Figure 2. WoL Magic Packet Example

So far, we have looked at two methods to save power using the Ethernet PHY. Consider which method you plan to implement in your system. You can share your thoughts with engineers at the TI E2E™ Community Ethernet Forum.