Differential Transmission Circuit Common Mode Suppression
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Solution Overview
Problem
Current techniques for suppressing unintentional electromagnetic radiation in differential transmission circuits, such as using metal cases and electromagnetic wave absorption materials, increase costs and face limitations in frequency band and circuit size, while existing common mode choke coils and differential amplification ICs have upper frequency limits and size constraints.
Innovation Solution
A differential transmission circuit design featuring a grounded conductive layer, transmission line conductors, a conductive film, and band rejection filter regions with specific geometries and dimensions to attenuate common mode signals at specific frequencies, reducing unintentional electromagnetic radiation without increasing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If metal case with small gap and electromagnetic wave absorption material are used to suppress electromagnetic radiation, then electromagnetic radiation is suppressed, but manufacturing cost increases
Solution Approach 1:
The invention extracts and targets specifically the common mode signal component that causes electromagnetic radiation, rather than suppressing all electromagnetic waves. By inserting a common mode choke coil that selectively increases impedance only for common mode signals, the solution eliminates the harmful radiation source without requiring comprehensive shielding structures like metal cases and absorption materials, thereby reducing manufacturing cost.
Solution Approach 2:
The common mode choke coil acts as an intermediary element inserted into the differential transmission line. It selectively interacts with common mode signal components by increasing their impedance, while allowing differential mode signals to pass through unaffected. This targeted intervention suppresses electromagnetic radiation from common mode noise without requiring expensive broad-spectrum electromagnetic shielding.
2Object-affected harmful factors
If common mode choke coil is inserted to suppress common mode signal, then electromagnetic radiation is reduced, but frequency band is limited
Solution Approach 1:
The invention designs the common mode choke coil with specific inductance values and impedance characteristics tailored to the operating frequency range of high-speed digital transmission (hundreds of Mbit/s to several Gbit/s). By optimizing the choke coil parameters (inductance, impedance, parasitic capacitance) for the target frequency band, the solution effectively suppresses common mode signals at these frequencies while maintaining signal integrity, providing adaptability to different high-speed transmission applications.
3Object-affected harmful factors
If differential amplification IC is used to suppress switching noise, then electromagnetic radiation is reduced, but circuit size increases
Solution Approach 1:
The invention extracts and addresses the common mode signal component separately from the differential signal transmission path. By inserting a common mode choke coil that specifically targets and suppresses common mode noise, the solution eliminates the need for complex differential amplification IC circuits, thereby reducing overall circuit size while effectively suppressing switching noise that causes electromagnetic radiation.
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 proposed solution effectively suppresses unintentional electromagnetic radiation across high frequencies while maintaining cost efficiency and reducing circuit size and power consumption, ensuring signal integrity and compatibility with high-speed digital transmission.
Implementation Method 1
a band rejection filter region in which the pair of transmission line conductors planarly overlaps the conductive film, when viewed from an upper side of the grounded conductive layer, and extends parallel to each other so as to have a second width narrower than the first width and a common mode of the differential transmission signal is attenuated at one of frequencies which are natural number multiples of a frequency corresponding to the predetermined bit rate
Data Source
AI summary
A differential transmission circuit includes a grounded conductive layer, a pair of transmission line conductors, a conductive film and a via hole which connects the grounded conductive layer to the conductive film. The differential transmission circuit further includes a straight-line region which is present in the differential transmission circuit through which a differential transmission signal output by a driving circuit is transmitted and in which the pair of transmission line conductors extends parallel so as to have a first width, and a band rejection filter region in which the pair of transmission line conductors planarly overlaps the conductive film and extends parallel so as to have a second width narrower than the first width and a common mode of the differential transmission signal is attenuated at one of the frequencies which are natural number multiples of a frequency corresponding to the predetermined bit rate.