Noise Suppression Filter Guide

Do you know about noise suppression for the new USB3.0 standard?

What is USB3.0?

In recent years, USB has become a standard interface that is almost always used on electronic devices. The latest higher standard USB3.0 is approximately ten times faster than the previous standard, and can send and receive large volumes of data in a short time.

What noise suppression components are suitable for USB3.0?

The digital circuits used in the myriad of electronic devices that surround us in our daily lives generate weak radio waves, and if these weak radio waves enter other electronic devices, this can cause operation errors or lower performance. For this reason, noise regulations are established for electronic devices that restrict the radiation noise to a certain level or less. USB cables can easily act as antennae, so noise is generally suppressed by adding noise suppression components to the base of USB connectors.
Common mode choke coils are often used as noise suppression components for USB. However, USB3.0 uses faster signals than the previous standard, so conventional common mode choke coils may affect the signal waveforms and hinder signal transfer.
Murata has therefore developed and commercialized the DLP11TB/RB series of chip common mode choke coils that have no adverse effects even on USB3.0 high-speed signals.

Introduction of noise suppression components that support USB3.0

~Common mode choke coils (*1) This is where the DLP11TB/RB series is different!~
The new product DLP11TB/RB series has been developed especially for USB3.0 noise suppression. Some of the features are introduced below.

*1 Noise suppression components used for USB/HDMI, etc.

# Highly efficient noise suppression effects

USB3.0 uses high-speed signals that generate strong noise in the GHz band, which is the high-frequency band. Therefore, the noise suppression effect peak of this product is set in the high-frequency GHz band, and the product is designed to efficiently suppress USB3.0 noise (Fig. 1).

Fig. 1 Radiation noise evaluation results

# Low signal deterioration

The USB3.0 standard specifies the circuit characteristic impedance (inherent impedance of the transfer path) as 90Ω. If the component characteristic impedance does not match the circuit characteristic impedance, high-speed signals cannot be transmitted properly. Therefore, the DLP11TB/RB series is designed with a component characteristic impedance of 90Ωto match the USB3.0 specification (Fig. 2). Of course, the signal cut-off frequency (*2) has also been increased to prevent signal deterioration (Fig. 3).

*2 The cut-off frequency is the frequency at which the signal starts to attenuate rapidly once that frequency is exceeded.

Characteristic impedance
Fig. 2 Characteristic impedance
Fig. 3 Eye pattern evaluation results

This product is available with three different common mode impedance values (*3): 80Ω, 40Ω and 15Ω (@100MHz).
*3 Common mode impedance is the physical property used as a reference for judging the common mode noise attenuation effects.

This column explained common mode choke coils as a noise suppression component. Murata also provides crystal resonators, Posistors, ESD protection devices, multilayer ceramic capacitors, and ferrite beads as USB3.0 compatible components. Please contact Murata Technical Support for information on these and other products.

 

person in charge : Murata Manufacturing Co., Ltd.  Kosuke Ishida

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