Passive Components Blog
No Result
View All Result
  • Home
  • NewsFilter
    • All
    • Aerospace & Defence
    • Antenna
    • Applications
    • Automotive
    • Capacitors
    • Circuit Protection Devices
    • electro-mechanical news
    • Filters
    • Fuses
    • Inductors
    • Industrial
    • Integrated Passives
    • inter-connect news
    • Market & Supply Chain
    • Market Insights
    • Medical
    • Modelling and Simulation
    • New Materials & Supply
    • New Technologies
    • Non-linear Passives
    • Oscillators
    • Passive Sensors News
    • Resistors
    • RF & Microwave
    • Telecommunication
    • Weekly Digest

    Smolteks CNF MIM Capacitor Break 1 µF/mm²

    Samsung Electro-Mechanics Releases 0201 X7T 1uF 6.3V MLCC for ADAS Applications

    Murata Announces 0402 Automotive Chip Ferrite Beads for V2X

    2025 Thick and Thin Film Resistor Networks Environment Overview

    Role of High-Q Ceramic Filters to Overcome GNSS Jamming

    Optimization of IoT for GEO NB-NTN Hybrid Connectivity

    TDK Releases Automotive Power-Over-Coax Inductor for Filters

    Advanced Conversion Announces Mass Production of 200C Film Capacitors

    VinaTech Supercapacitors: Enhancing Smart Meter Reliability and Efficiency

    Trending Tags

    • Ripple Current
    • RF
    • Leakage Current
    • Tantalum vs Ceramic
    • Snubber
    • Low ESR
    • Feedthrough
    • Derating
    • Dielectric Constant
    • New Products
    • Market Reports
  • VideoFilter
    • All
    • Antenna videos
    • Capacitor videos
    • Circuit Protection Video
    • Filter videos
    • Fuse videos
    • Inductor videos
    • Inter-Connect Video
    • Non-linear passives videos
    • Oscillator videos
    • Passive sensors videos
    • Resistor videos

    Understanding Switched Capacitor Converters

    Coupled Inductors Circuit Model and Examples of its Applications

    Inductor Resonances and its Impact to EMI

    Highly Reliable Flex Rigid PCBs, Würth Elektronik Webinar

    Causes of Oscillations in Flyback Converters

    How to design a 60W Flyback Transformer

    Modeling and Simulation of Leakage Inductance

    Power Inductor Considerations for AI High Power Computing – Vishay Video

    Coupled Inductors in Multiphase Boost Converters

    Trending Tags

    • Capacitors explained
    • Inductors explained
    • Resistors explained
    • Filters explained
    • Application Video Guidelines
    • EMC
    • New Products
    • Ripple Current
    • Simulation
    • Tantalum vs Ceramic
  • Knowledge Blog
  • Suppliers
    • Who is Who
  • Events
  • Home
  • NewsFilter
    • All
    • Aerospace & Defence
    • Antenna
    • Applications
    • Automotive
    • Capacitors
    • Circuit Protection Devices
    • electro-mechanical news
    • Filters
    • Fuses
    • Inductors
    • Industrial
    • Integrated Passives
    • inter-connect news
    • Market & Supply Chain
    • Market Insights
    • Medical
    • Modelling and Simulation
    • New Materials & Supply
    • New Technologies
    • Non-linear Passives
    • Oscillators
    • Passive Sensors News
    • Resistors
    • RF & Microwave
    • Telecommunication
    • Weekly Digest

    Smolteks CNF MIM Capacitor Break 1 µF/mm²

    Samsung Electro-Mechanics Releases 0201 X7T 1uF 6.3V MLCC for ADAS Applications

    Murata Announces 0402 Automotive Chip Ferrite Beads for V2X

    2025 Thick and Thin Film Resistor Networks Environment Overview

    Role of High-Q Ceramic Filters to Overcome GNSS Jamming

    Optimization of IoT for GEO NB-NTN Hybrid Connectivity

    TDK Releases Automotive Power-Over-Coax Inductor for Filters

    Advanced Conversion Announces Mass Production of 200C Film Capacitors

    VinaTech Supercapacitors: Enhancing Smart Meter Reliability and Efficiency

    Trending Tags

    • Ripple Current
    • RF
    • Leakage Current
    • Tantalum vs Ceramic
    • Snubber
    • Low ESR
    • Feedthrough
    • Derating
    • Dielectric Constant
    • New Products
    • Market Reports
  • VideoFilter
    • All
    • Antenna videos
    • Capacitor videos
    • Circuit Protection Video
    • Filter videos
    • Fuse videos
    • Inductor videos
    • Inter-Connect Video
    • Non-linear passives videos
    • Oscillator videos
    • Passive sensors videos
    • Resistor videos

    Understanding Switched Capacitor Converters

    Coupled Inductors Circuit Model and Examples of its Applications

    Inductor Resonances and its Impact to EMI

    Highly Reliable Flex Rigid PCBs, Würth Elektronik Webinar

    Causes of Oscillations in Flyback Converters

    How to design a 60W Flyback Transformer

    Modeling and Simulation of Leakage Inductance

    Power Inductor Considerations for AI High Power Computing – Vishay Video

    Coupled Inductors in Multiphase Boost Converters

    Trending Tags

    • Capacitors explained
    • Inductors explained
    • Resistors explained
    • Filters explained
    • Application Video Guidelines
    • EMC
    • New Products
    • Ripple Current
    • Simulation
    • Tantalum vs Ceramic
  • Knowledge Blog
  • Suppliers
    • Who is Who
  • Events
No Result
View All Result
Passive Components Blog
No Result
View All Result

Be Careful with Input-Output Feedback in Filters

1.7.2019
Reading Time: 4 mins read
A A

Source: InCompliance article

by Arturo Mediano.

RelatedPosts

Smolteks CNF MIM Capacitor Break 1 µF/mm²

Samsung Electro-Mechanics Releases 0201 X7T 1uF 6.3V MLCC for ADAS Applications

Murata Announces 0402 Automotive Chip Ferrite Beads for V2X

When designing EMI filters, how and where the filter is installed is critical to obtain the desired insertion losses. Usually, the effect of a wrong location or installation is not considered in the design of the filter and surprises appear.

A few weeks ago I was working on a product of a company failing in conducted emissions. The product was powered from 240V 50Hz (Europe) mains network consuming 10A and a custom filter was included in the design to try to pass the regulations for conducted emissions in the 9kHz-30MHz range.

The schematic of the filter used in this product is included in Figure 1. The filter was composed of two 100nF X2 capacitors, one 470uH common mode choke, and two 4.7nF capacitors.

Figure 1: Schematic of the filter under study.

But, the results obtained in the EMC test house by the company were really bad (>20dB) compared with the expected results from theory and simulation in the range from 1MHz to 10MHz.

When a filter is not working as expected I usually check some typical points:

  • What terminal impedances were used in the design? Many designers use 50ohms because this is a good value for testing the filter with common RF instruments. But, if your product does not present 50ohms impedance, surely the behavior of the filter will be different [1].
  • Are the inductors used in the filter being saturated? This is more typical in differential mode filters but sometimes leakage or external magnetic fields can saturate common mode chokes.
  • Were the parasitics of components (especially self-resonant frequencies) included in the design process? Usually, the frequencies higher than 1MHz are compromised especially if big inductors and capacitors are needed.
  • Where is the filter installed? A good location for the filter is far from noisy areas. As, for example, floating power electronic heat sinks. This is critical if the filter is non-shielded.

In my analysis, I was able to identify that none of the previous effects were the origin of the problem so I went to check how the filter was wired and I found that the input and the output of the filter were really close to each other. This is a dangerous situation, especially for the high frequency range.

I have partially reproduced the effect so you can understand the idea (exact identification and pictures of the system remain confidential).

Consider, for example, that you have a filter shielded as the one in Figure 2. Note that, in theory, we will be expecting a low pass differential filtering response.

Figure 2: Filter used in our example in “ideal” layout.


Now, consider Figure 3 where the filter is installed with input and output cables close to each other.

Figure 3: Filter used in our example with a short distance between input and output wires.


Now, the position of cables creates some kind of coupling between the input and the output of the filter. This coupling can be capacitive (electric field) and inductive (magnetic field) so the theoretical low pass filter response is “short-circuited” and the signals can go from the input to the output easily (especially in the high frequency range). In Figures 2 and 3, I am not considering the parasitic effects of components.

To check the installation of the filter in our product, I used my Bode 100 network analyzer with the product OFF. The results are included in Figure 4.

Figure 4: Measured response of the filter with good-bad routing of input-output wires.


Note the response at low frequencies (<600kHz) is not affected by the parasitic IO feedback. But, it is degraded up to 30dB in the 1-10MHz frequency range when IO feedback is present similar to Figure 3.

It is interesting to note from our measurements the peak in the response at 361kHz (cursor 1, green). This is a very dangerous situation if the peak goes over 0dB and not related with the IO feedback (topic for a future article).

Note, too, how the low pass response in the filter is dominated by parasitic in components at frequencies higher than 2.5MHz (cursor 2, orange).

My final advice: when doing the layout for a filter in both wired or PCB formats, BE CAREFUL with the I/O feedback. Try to route the lines correctly to minimize the parasitic feedback that degrades the filter response in high frequencies.

References

  1. A. Mediano, “S Parameters and EMI Filter Response,” pp. 15-17, In Compliance Magazine, August 2018.

Related

Recent Posts

Smolteks CNF MIM Capacitor Break 1 µF/mm²

19.6.2025
16

Samsung Electro-Mechanics Releases 0201 X7T 1uF 6.3V MLCC for ADAS Applications

19.6.2025
6

Murata Announces 0402 Automotive Chip Ferrite Beads for V2X

19.6.2025
14

Role of High-Q Ceramic Filters to Overcome GNSS Jamming

19.6.2025
13

Optimization of IoT for GEO NB-NTN Hybrid Connectivity

19.6.2025
4

TDK Releases Automotive Power-Over-Coax Inductor for Filters

18.6.2025
6

Advanced Conversion Announces Mass Production of 200C Film Capacitors

18.6.2025
15

VinaTech Supercapacitors: Enhancing Smart Meter Reliability and Efficiency

17.6.2025
13

Bourns Introduces New Automotive Grade BMS Signal Transformer

17.6.2025
7

Bourns Introduces 1206 Multilayer Common Mode Filters

16.6.2025
8

Upcoming Events

Jun 24
16:00 - 17:00 CEST

Limitations of PSFB converters and improvements by a variable inductor ft. Sam Ben-Yaakov

Jun 24
17:00 - 18:00 CEST

Ultra-Compact and Efficient Switched-Capacitor Power Converters

Jul 23
13:00 - 14:00 CEST

PCB design for a Smartwatch

View Calendar

Popular Posts

  • Buck Converter Design and Calculation

    0 shares
    Share 0 Tweet 0
  • Boost Converter Design and Calculation

    0 shares
    Share 0 Tweet 0
  • Flyback Converter Design and Calculation

    0 shares
    Share 0 Tweet 0
  • What is a Dielectric Constant and DF of Plastic Materials?

    4 shares
    Share 4 Tweet 0
  • LLC Resonant Converter Design and Calculation

    0 shares
    Share 0 Tweet 0
  • Ripple Current and its Effects on the Performance of Capacitors

    3 shares
    Share 3 Tweet 0
  • How to Design an Inductor

    0 shares
    Share 0 Tweet 0
  • Dual Active Bridge (DAB) Topology Explained

    0 shares
    Share 0 Tweet 0
  • SEPIC Converter Design and Calculation

    0 shares
    Share 0 Tweet 0
  • Flying Capacitors Explained

    0 shares
    Share 0 Tweet 0

Newsletter Subscription

 

Passive Components Blog

© EPCI - Leading Passive Components Educational and Information Site

  • Home
  • Privacy Policy
  • EPCI Membership & Advertisement
  • About

No Result
View All Result
  • Home
  • Knowledge Blog
  • Premium Suppliers

© EPCI - Leading Passive Components Educational and Information Site

This website uses cookies. By continuing to use this website you are giving consent to cookies being used. Visit our Privacy and Cookie Policy.
Go to mobile version