As digitalization becomes more deeply integrated into every aspect of our lives, the amount of data constantly exchanged between different devices and machines is also increasing. Especially in the industrial sector, traditional communication technologies are beginning to reach their limits, and Ethernet (in this case, Industrial Ethernet) is emerging as the new standard. With Ethernet, gigabit-level data rates can be achieved over distances of up to 100 meters, and even several kilometers using fiber optic cables.
Ethernet is an interface specification defined in IEEE 802.3. The Ethernet Physical (PHY) layer is one element of IEEE 802.3. It is a transceiver component used to send and receive data or Ethernet frames. In the OSI model, Ethernet covers a portion of Layer 1 (Physical Layer) and Layer 2 (Data Link Layer).
The physical layer specifies the electrical signal type, signal rate, media and connector type, and network topology. Ethernet PHYs can be mapped to this layer, as shown in Table 1.
Table 1 OSI Model
The PHY (Physical Interface) constitutes the physical interface, responsible for encoding and decoding data transmitted between the purely digital system and the signal transmission medium. Therefore, it represents the bridge between the digital connection layer and the electronic connection layer of the interface.
The data link layer defines how communication occurs over the medium, and the frame structure for transmitting and receiving messages. This means it defines how the bits from the line are arranged to extract data from the bit stream. In Ethernet, this is called Media Access Control (MAC), which is adjacent to the PHY, but it's located at the data link layer. MAC is typically integrated into a controller or switch.
The PHY can be a discrete component or integrated into the Ethernet controller. A simplified block diagram in Figure 1 shows the required Ethernet components and a discrete PHY.
If the design must use a discrete PHY, then several criteria should be kept in mind when selecting a PHY.
1. Several important criteria to consider when selecting an industrial PHY
In industrial applications, data transmission and networks must maintain high reliability and be fail-safe over a wide temperature range. All components must meet this requirement.
(1) Network cycle time
Network cycle time is the time required for the controller to collect and update data from connected devices. A low-latency PHY can shorten network cycle time, thereby improving network update time, which is crucial for time-critical applications. This allows more devices to be connected to the network.
(2) Anti-interference capability/robustness
The working environment in industrial applications is often harsh. The PHY is directly connected to or connected to the cable via small magnetic components, and these connections can introduce interference (radiation or conduction), so the PHY must be able to withstand common external conditions.
Figure 1. Simplified block diagram of Ethernet connection
EMC standards such as CISPR 32, IEC 61000-4-2 to IEC 61000-4-6 can serve as benchmarks for PHY specifications. A reliable PHY helps in obtaining certification and avoids the often cumbersome redesign work.
(3) Loss and temperature range
Devices used in industrial applications typically employ IP65/IP66 dust and moisture protection, which limits airflow for cooling the electronics. Simultaneously, devices in industrial applications often need to withstand high-temperature environments. Furthermore, linear and ring topologies often require two Ethernet connections, necessitating two PHYs, which doubles the PHY losses associated with data input and output. Therefore, low-loss PHYs should be selected to minimize device self-heating.
ADI places great emphasis on various industrial requirements when developing industrial Ethernet PHYs and has launched a number of reliable PHYs, including ADIN1200 (10 Mbps/100 Mbps), ADIN1300 (10 Mbps/100 Mbps/1 Gbps) and ADIN1100 (10BASE-T1L), to complement and enhance its ADI Chronous™ industrial Ethernet product family.
