Interface Circuit Common Mode Noise Suppression
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Solution Overview
Problem
Conventional interface circuits generate noise due to instantaneous discharge of the common mode capacitor when switches are turned on, affecting signal integrity in high-speed differential signal modes.
Innovation Solution
An interface circuit with a common mode potential adjustment circuit, utilizing diodes or field-effect transistors, is introduced to adjust the common mode potential based on channel voltages, providing discharge paths to suppress noise during switch activation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If switches SW1 and SW2 are turned on to connect terminal resistors to common mode capacitor, then common mode potential is established, but noise is generated due to instantaneous discharge
Solution Approach 1:
The patent applies preliminary action by pre-charging the common mode capacitor through dedicated charging paths (first charging path including first charging switch and second charging path including second charging switch) before the main switches SW1 and SW2 are turned on. This ensures the capacitor is already at the required potential level, eliminating the need for instantaneous discharge when switches close, thereby preventing noise generation while maintaining reliable signal integrity
Solution Approach 2:
The patent segments the capacitor control function into separate charging paths and switching stages. Instead of a single switching action, the system uses multiple independent charging paths with their own switches to gradually establish the common mode potential, separating the charging function from the signal transmission function to avoid noise coupling into the signal channels
Data Source
AI summary
An interface circuit includes a receiver, a first terminal resistor, a second terminal resistor, a common mode capacitor, a first switch, a second switch, and a common mode potential adjustment circuit. The receiver includes a first channel for receiving a first channel voltage, and a second channel for receiving a second channel voltage. The common mode capacitor provides a common mode potential. The first switch electrically connects the first terminal resistor to the common mode capacitor, and the second switch electrically connects the second terminal resistor to the common mode capacitor. The common mode potential adjustment circuit is coupled to the first switch, the second switch and the common mode capacitor, and adjusts the common mode potential according to the first channel voltage and the second channel voltage.