This article takes you to understand those factors to pay attention to when choosing an Ethernet PHY!

“As digitization becomes more deeply integrated into every aspect of our lives, so does the amount of data that is continuously exchanged between different devices and machines. Especially in the industrial sector, traditional communication technologies are starting to reach their limits and Ethernet (in this case Industrial Ethernet) is starting to become the new standard. With Ethernet, higher data rates in the gigabit class can be achieved over distances of up to 100 meters, or even several kilometers if fiber optic cables are used.

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As digitization becomes more deeply integrated into every aspect of our lives, so does the amount of data that is continuously exchanged between different devices and machines. Especially in the industrial sector, traditional communication technologies are starting to reach their limits and Ethernet (in this case Industrial Ethernet) is starting to become the new standard. With Ethernet, higher data rates in the gigabit class can be achieved over distances of up to 100 meters, or even several kilometers if fiber optic cables are used.

Ethernet is an interface specification specified in IEEE 802.3. The Ethernet Physical (PHY) layer is one of the elements of IEEE 802.3. It is a transceiver component that sends and receives data or Ethernet frames. In the OSI model, Ethernet covers part of layer 1 (physical layer) and layer 2 (data link layer).

The physical layer specifies electrical signal types, signal rates, media and connector types, and network topology. Ethernet PHYs can be mapped into this layer, as shown in Table 1.

Table 1. OSI model

The PHY constitutes the physical interface and is responsible for encoding and decoding the data transmitted between the purely digital system and the signal transmission medium. Therefore, it represents a bridge between the digital connection layer and the Electronic connection layer of the interface.

The data link layer defines the way communication takes place over the medium, and the frame structure for transmitting and receiving messages. That means, it defines how the bits from the wire are arranged to extract data from the bitstream. In Ethernet, this is called Medium Access Control (MAC), which is right next to the PHY, but in the data link layer. The MAC is usually integrated into the controller or switch.

The PHY can be a discrete component or integrated into the Ethernet controller. The required Ethernet components and discrete PHYs are shown in the simplified block diagram of Figure 1.

Figure 1. Simplified block diagram of an Ethernet connection.

If a design must use a discrete PHY, there are several criteria to keep in mind when choosing a PHY.

Several important criteria to consider when choosing an industrial PHY

In industrial applications, data transmission and networks must be highly reliable and fail-safe over a wide temperature range. Required for all components.

1 Network cycle time

Network cycle time is the time it takes the controller to collect and update data from connected devices. A PHY with low latency can reduce network cycle time, thereby improving network update time, which is critical for time-critical applications. This allows more devices to be connected to the network.

2 Anti-jamming capability/robustness

Working environments in industrial applications are often harsh. The PHY is connected directly to the cable or through small magnetic components to the cable, and these connections can introduce interference (radiated or conducted), so the PHY must be able to withstand common external conditions.

EMC standards such as CISPR 32, IEC 61000-4-2 to IEC 61000-4-6, etc. can be used as benchmarks to measure PHY specifications. A reliable PHY facilitates certification and avoids the often tedious redesign effort.

3 Loss and temperature range

Devices used in industrial applications are typically IP65/IP66 rated for dust and moisture protection, which restricts the airflow used to cool the electronics. At the same time, devices in industrial applications often need to withstand high temperature environments. Additionally, in line and ring topologies, two Ethernet connections are typically required, and therefore two PHYs, doubling the PHY losses associated with data input and output. Therefore, a PHY with low loss should be selected to minimize the self-heating of the device.

4 External PHYs from Analog Devices

Analog Devices has developed Industrial Ethernet PHYs with a strong focus on industrial requirements and has introduced several reliable PHYs including the ADIN1200 (10 Mbps/100 Mbps), ADIN1300 (10 Mbps/ 100 Mbps/1 Gbps) and ADIN1100 (10BASE -T1L) to complement and complete its Industrial Ethernet ADI Chronous™ product line.