Noise Suppression Filter Guide

Case Study of AVN Car Navigation System Noise Countermeasure with common mode choke coil "PLT10HH"series

Previously, we introduced a case study of an onboard motor noise countermeasure using the PLT10HH. This time we follow up with a case study of an example using the PLT10HH in the power supply block of an AVN car navigation system.
The earlier article introducing the case study of an onboard motor noise countermeasure can be found at the following
URL:https://article.murata.com/article/onboard-motor-noise-countermeasure-with-plt10hh

An earlier article introducing the PLT10HH can be found at the following
URL:https://article.murata.com/article/common-mode-choke-coils-for-automotive

AVN car navigation system noise countermeasure

Car navigation systems have diverged into enhanced function AVN (Audio Video Navigation) integrated types and low-cost PND (Portable Navigation Device) types. However, AVN types are not limited to just AVN functions, and are increasingly incorporating diverse functions such as external communication for the purpose of gathering information, and confirmation of safety around the vehicle using multiple cameras. Recently, models have appeared that display various information superposed onto the real-time image on the navigation system screen, like in a science fiction movie. With this enhanced functionality, the speeds and functions of the internal processing elements are also increasing, with the result that much noise is generated. On the other hand, automobiles also use digital devices other than navigation systems, and there is the issue that noise generated by these devices may flow into the navigation system. AVN navigation systems receive radio waves over a wide frequency range from AM radio frequencies to GPS and communications frequencies, so the inflow of noise must also be prevented over a wide frequency range. Most AVN navigation systems use a metal cabinet, so little noise exits or enters the set directly. However, the power cable can easily become an issue as an inflow and outflow path for noise.

Fig. 1: AVN navigation system noise environment

AVN navigation systems contain both noise sources and circuits susceptible to noise, so care must be given to noise inflow and outflow via the power cable.

The navigation system power line is of course connected with the power lines of various electronic devices in the automobile, so noise from various ECU (Electronic Control Unit) and motors enters via the power line, and noise flowing out from the navigation system also affects these devices. This makes noise countermeasures for the navigation system power line quite important.

 

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Case study of car navigation system noise countermeasure with PLT10HH

As a result of enhanced navigation system functionality, the current flowing through the power line has increased as high as approximately 10 A, so parts requiring noise countermeasures must support large currents.
The PLT10HH series of SMD-type common mode choke coils support large currents of up to 10 A, making them suitable for suppressing the radiation and inflow of common mode noise, which easily becomes an issue for the power cable. This case study measured the externally radiated noise from the set, and investigated the noise countermeasure effects of using the PLH10HH1026R0 (rated current: 6 A) in the power supply connector block.
PLT10HH product information can be found at the following URL:
PLT10HH series

Fig. 2: Noise evaluation circuit

The results confirmed noise countermeasure effects over a wide frequency band as shown in Fig. 3. This case study evaluated a countermeasure for externally radiated noise from the car navigation system, but common mode choke coils are similarly effective against external noise entering via cables. This makes them an effective means of protecting navigation systems from noise.

Fig. 3: Noise countermeasure effects

Other countermeasures include the use of ring cores for cables, but in this case the number of windings cannot be increased, so sufficient effects often cannot be achieved for low-frequency noise. In addition, when the cable is wrapped around the ring two or more times, line capacitance occurs between adjacent windings, and high-frequency noise can bypass the ring core via this capacitance, with the result that the high-frequency response worsens. The PLT10HH uses a winding method that also takes into account the high-frequency response, enabling effective countering of noise over a wide range from low to high frequencies.

Fig. 4: Issue when using a ring core

As described above, the PLT10HH is an ideal common mode choke coil for various noise countermeasures in automobiles, such as for onboard motors and car navigation systems. Furthermore, in addition to automotive applications, it is also suitable as a noise countermeasure part for factory automation equipment, amusement machines, and other applications that use large currents and require noise reduction over a wide frequency range.

 

Written by: Y.M., Murata Manufacturing Co., Ltd.

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