Ethernet Transformers – High Quality Due to Automated Production

09/04/2023 Know-How

As the interface between the device and the Ethernet cable, Ethernet transformers perform a key role. Thanks to a new design, they are now available in large quantities and high quality for the fast-growing market of Ethernet networks.

Based on the advances in production technology and the introduction of efficient coding processes, modern-day Ethernet networks can achieve transmission rates of up to 40 Gbit/s and 100 Gbit/s for copper and fiber-optic networks respectively. The widespread use of Ethernet enables the most cost-effective digital networks. So, it comes as no surprise that the number of Ethernet networks is increasing all the time. Consequently, the vast majority of end devices for industrial, communication, transportation, and consumer markets is interconnected via Ethernet networking.

A critical component used in Ethernet networks is the transformer. As the interface between the device and the Ethernet cable, it performs a key role: It provides safety-relevant galvanic isolation between digital circuitry, which forms the data link layer for Ethernet systems, and PHY (physical layer) (Fig. 1), which converts digital signals to analog ones. At the same time, the Ethernet transformer is responsible for impedance matching and data transmission. The transmit and receive signals should be attenuated as little as possible.

The transformer consists of four windings, of which two windings are used on the primary side for the digital interface, and the other two windings are on the secondary side connected to twisted pair wires via the RJ45 connector.

The H1190NL transformer from Pulse, which provides 1,500 Vrms or 2,250 V DC electrical isolation as specified by IEEE 802.XX, derived from IEC standard 62368-1, eliminates potential high-voltage exposure caused, for example, by electrical shorts in building wiring. This is accomplished by a magnetic coupling that allows transfer of electrical signals from the primary to the secondary side while providing the required safety function.

Higher quantities and improved quality thanks to automated production

Until quite recently, the amount of manual labor involved in the production of ferrite toroidal core transformers was still relatively high, since the magnet wires had to be connected to the contacts and pins by hand – a time- and cost-intensive process. Further, the risk of impedance mismatch is very high in manual production processes, which can cause a decrease in both the maximum usable bandwidth and the data transmission rate. To meet the increasing demand for transformers while improving component quality, Pulse invested in automated transformer winding equipment for the production of the T-chip series (TC1000/2500/5000/10000) (Fig. 2). The transformers are now wound fully automatically onto a bobbin-shaped core with plated contacts for wire terminations. Another advantage of fully automated production: A visual inspection to ensure correct winding is no longer required.

In addition to lower costs resulting from shorter production times and improved production yield, the T-chip series transformers offer many other advantages. The technology integrates the mechanical package around the ferrite core, thereby eliminating the need for a plastic housing. The transformers are thus lighter and smaller compared to traditional toroidal core models.

Generally speaking, T-chip transformers support the same data rates as toroidal core designs. Moreover, they meet standards IEE802.3xx for data transmission rates of 100 Mbit/s to 10 Gbit/s and provide up to 600 mA of PoE (power over Ethernet) to power remote end devices.

Quality features of T-chip transformers

In addition to crosstalk, common mode rejection, and return loss, a decisive quality feature of transformers is insertion loss. It describes the loss of transmission power from the power source to the load and represents the transmitted signal power that is lost between input and output. The insertion loss is closely related to the possible range or cable length.

The diagrams in Fig. 3 illustrate the insertion loss of 1 Gbit/s transformers, once with a toroidal and once with a T-chip design. The measurement curves show that LAN transformers with a T-chip design have a reduced scatter of electrical parameters and better values.


T-chip technology enables the production of high-quality Ethernet transformers for a myriad of networking applications. Beside the quality of the components, an EMC or HF-compatible environment and an appropriate PCB layout are crucial factors to guarantee top-quality Ethernet networks.


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Ethernet Transformers - High Quality Due to Automated Production

The transformer isolates digital circuitry from PHY (physical layer)

Transformers wound semi-automatically (a) and fully automatically (b)

Comparison of insertion loss for toroidal and T-chip transformers