Differential Transmission Circuit Common Mode Choke Noise Suppression
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Solution Overview
Problem
Conventional differential transmission circuits suffer from power source noise propagation and electromagnetic interference due to direct connections between power source/ground lines and differential signal lines via resistive elements, leading to radiation of electromagnetic noise.
Innovation Solution
Incorporating a common mode choke coil with magnetically coupled coil units connected between the power source/ground lines and resistor groups, which increases impedance to in-phase noise components, thereby suppressing power source noise propagation and reducing electromagnetic noise radiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the power source line/ground line is connected directly to the differential signal lines via resistive elements in the level shift circuit, then the direct-current voltage levels can be adjusted to the required standards, but power source noise propagates to the differential signal lines causing electromagnetic interference
Solution Approach 1:
The patent introduces a common mode choke coil as an intermediary component between the power source line and the differential signal lines. The choke coil's inductance provides high impedance to high-frequency noise currents while allowing direct-current voltage to pass through, thereby blocking noise propagation without affecting the voltage level shifting function of the resistive elements
Solution Approach 2:
The patent utilizes the frequency-dependent impedance characteristic of the common mode choke coil. At direct-current frequencies, the choke coil presents low impedance allowing voltage adjustment, while at high-frequency noise ranges, it presents high impedance blocking noise propagation. This parameter change with frequency resolves the contradiction between enabling noise-free power delivery and maintaining voltage level adjustment capability
2Adaptability or versatility
If resistive elements are used for level shifting in the differential transmission circuit, then signal level compatibility between different standards is achieved, but power source noise flows equally into both sides of the differential signal line with the same phase
Solution Approach 1:
The common mode choke coil acts as a mediator that selectively blocks in-phase noise currents while allowing the differential signal and direct-current voltage to pass. The choke coil's position in the common path of both signal lines enables it to suppress common-mode noise without affecting the differential signal transmission or the level shifting function
Solution Approach 2:
The patent converts the harmful in-phase noise that flows through the resistive elements into a beneficial filtering opportunity. By placing the common mode choke coil in the power source path, the same current path that carries the noise also carries the filtering action of the choke coil, transforming the noise propagation path into a noise suppression path
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 solution effectively reduces power source noise propagation to resistor groups and minimizes electromagnetic noise radiation, enhancing the stability and performance of high-speed digital transmission systems.
Implementation Method 1
a first common mode choke coil including a first coil unit adapted to connect one of the power source and ground lines with one end of the first resistor group and a second coil unit adapted to connect the one of the lines with one end of the second resistor group and magnetically coupled to the first coil unit
Data Source
AI summary
A first resistor group and second resistor group are respectively made up of at least three resistive elements connected in series and are adapted to shift respectively direct-current voltage levels of a first signal and second signal to voltage levels obtained by dividing a direct-current voltage between a power source line and ground line. A common mode choke coil is installed between the power source line and the first and second resistor groups. The common mode choke coil includes a first coil unit adapted to connect the power source line with one end of the first resistor group, and a second coil unit adapted to connect the power source line with one end of the second resistor group and magnetically coupled to the first coil unit. This suppresses propagation of power source noises of the same phase to the resistor groups.