Ethernet
Crystal
Keep the XTAL as close as possible to the IC. Where applicable connect the XTAL housing to GND. A via fence reduces coupling to the GND plane. An oscillator can be used alternatively.
Load Capacitor
Load capacitors should be low leakage and stable across temperature range (NP0). For the capacitive load (cload) the stray capacitance of the PCB and the IC pins should be considered:
CL = (C1*C2) / (C1+C2) + Cstray
Cstray ≈ 3…6pF
ESD Protection
ESD protection devices should be put right behind the connector. Avoid layer hops to prevent propagation of the ESD.
MLCC - Multilayer Ceramic Chip Capacitor 50 V
This Capacitor increases common mode rejection by balancing the center tap of the transformer. Depending on the PHY’s architecture, the circuitry around the termination resistors can be different.
MLCC - Multilayer Ceramic Chip Capacitor 3 kV
Isolation of 1.5 kV AC is required by the standard, which makes MLCCs with only 2 kV insufficient.
MLCC - Multilayer Ceramic Chip Capacitor 2 kV
This capacitor diverts common mode noise to Chassis Ground. Because of the capacitors dc blocking property, a rated voltage of 2 kV is chosen, to avoid inadvertent potential equalization and damaging of the component.
Common Mode Filter
On differential datalines, a CMC filters common mode noise without affecting the useful signal.
Common Mode Filter
On differential datalines, a CMC filters common mode noise without affecting the useful signal.
Signal Transformer
The Ethernet standard requires electrical isolation to avoid potential equalisation of different interconnected devices via the interface. Most LAN transformers already integrate the appropriate common-mode filters.
Signal Transformer
The Ethernet standard requires electrical isolation to avoid potential equalisation of different interconnected devices via the interface. Most LAN transformers already integrate the appropriate common-mode filters.
Intergated RJ 45 Transformer
The series WE-RJ45 LAN integrates the filter as well as the necessary transformer in one component. HPLE type RJ45 Transformers contain a second CMC to decrease EMI and increase performance.
Modular Jack
Select SMT, THT or THR types for optimized processing. We support 45°, vertical and horizontal versions. Fitting to your needs we have them in different shielding options, like non shielded, shielded and fully shielded and additional you can choose from a wide range of LED options.
Integrated M12 Transformer
The series WE-LANMX integrates the filter as well as the necessary transformer in one component.
XTAL Ground
This GND plane should be connected to IC GND and cover all the traces to the XTAL.
Grounding Scheme
RF coupling of the cable shield and PCB ground to chassis will short common mode noise in both directions. For best results this coupling should be symmetrical, meaning a capacitor both on the left and right Shielding Pins of the connector. For more information please refer to our Application Note 116.
Short Introduction to Ethernet
Ethernet is a common interface for computers, routers, switches and other devices in a cabled network. Ethernet is covered by several standards. While most of them use the same connector, their data rate is different. 100BASE-T means that the interface can transfer 100 Mbit/s on the Baseband over a twisted pair cable.
Enhanced data rates for standards 1000BASE-T and 10GBASE-T are achieved by using additional twisted pairs and increasing transmission speed.
Reference Designs
RD022 GB PoE+-Ethernet-USB“ adapter for industrial use with an EMC perspective
RD016 Reference Design Gigabit Ethernet Front End
