Differential Delay Line Common Mode Filter for Noise Absorption
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Common mode choke coils used in high-speed serial transmission systems suffer from high series impedance, leading to peak voltage increases and electromagnetic interference due to reflected common mode noise, which is difficult to shield and radiate externally.
Innovation Solution
A common mode filter comprising a lumped-constant differential delay line with inductors and capacitors in a ladder network, combined with a noise attenuating passive two-terminal network using resistors and inductors, effectively reduces peak voltage and absorbs common mode noise, preventing electromagnetic interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a common mode choke coil with larger inductance is used to cut off common mode noise, then the common mode noise is effectively blocked, but the peak voltage of the common mode noise increases at the input terminal due to reflection
Solution Approach 1:
The invention converts the reflected common mode noise, which was previously harmful, into a beneficial effect by deliberately designing a transmission zero at the input terminal frequency. The reflection that occurs is controlled and timed to cancel the incident common mode noise through destructive interference, transforming the harmful reflected wave into a noise-cancellation mechanism
Solution Approach 2:
The invention changes the electrical parameters (impedance, phase) at the input terminal by introducing a specific circuit configuration with transmission zeros positioned at the common mode noise frequency. This parameter transformation creates the conditions for destructive interference, reducing the peak voltage and preventing electromagnetic radiation while maintaining noise blocking
2Object-affected harmful factors
If a common mode choke coil is used to remove common mode noise, then the common mode noise is attenuated, but electromagnetic interference occurs due to radiation from the input terminal
Solution Approach 1:
The invention converts the potentially radiating reflected noise into a beneficial cancellation mechanism. By positioning transmission zeros at the input terminal, the reflected common mode noise is controlled to interfere destructively with the incident noise, transforming what would be radiating electromagnetic interference into a noise-reduction effect
3Speed
If differential lines are used for high-speed serial transmission, then electromagnetic field coupling prevents signal radiation, but common mode noise is generated and easily radiated
Solution Approach 1:
The invention extracts the common mode noise component from the differential signal transmission system by introducing a dedicated noise cancellation mechanism at the input terminal. The transmission zero configuration specifically targets and removes the common mode noise component, allowing the differential signal to be transmitted while preventing the extraction and radiation of common mode noise
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The filter enables high-speed differential signal transmission while effectively cutting off common mode noise and reducing electromagnetic interference by absorbing and attenuating the noise, thus preventing radiation.
Implementation Method 1
a lumped-constant differential delay line which is formed by arranging inductors, being passive series elements, and capacitors, being passive parallel elements
Implementation Method 2
capacitors, being passive parallel elements, in a ladder-shaped differential four terminal network
Implementation Method 3
noise attenuating passive two terminal network connected between a connection point of the capacitors connected in series and a ground potential, including resistors for attenuating the common mode noise
Implementation Method 4
a series circuit of the inductors and the resistors, or a parallel circuit of the inductors and the resistors
Data Source
AI summary
There is provided a common mode filter capable of allowing an ultrahigh speed differential signal to transmit and hardly allowing a common mode noise to transmit, comprising: a lumped-constant differential delay line DL formed by arranging inductors Lo, being passive series elements, and capacitors Co, being passive parallel elements, in a ladder-shaped differential four terminal network composed of the passive series elements and the passive parallel elements arranged in the differential lines 1, 3. In the lumped-constant differential delay line DL, the capacitors Co, being the parallel elements, are formed of two capacitors connected in series equivalent to each other and having same values with each other such as Co/2 and Co/2, or Co and Co. Inductors L1 to L4 and resistors R1 to R4 for attenuating the common mode noise are connected between connection points T1 to T4 of the capacitors Co/2 or Co connected in series, and a ground potential, thus forming a common mode noise attenuating series resonance circuit together with the capacitors Co/2, Co.