Capacitive Isolator Circuit for Common-Mode Noise Suppression
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing signal isolator devices are vulnerable to common mode current flow across isolation barriers, which can lead to signal corruption due to electro-magnetic transients, especially in noisy environments.
Innovation Solution
A common mode suppression circuit using a differential capacitive communications channel with a current mirror circuit is employed to detect common mode voltage movement and inject a corresponding signal to cancel detrimental displacement currents, ensuring that the current level is maintained across a resistor network, thereby suppressing common mode movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a differential capacitive communication channel is used to achieve galvanic isolation, then data transmission between isolated systems is enabled, but common mode voltage transients cause signal corruption
Solution Approach 1:
A common mode suppression circuit is introduced as an intermediary component between the capacitive communication channel and the receiver. This circuit includes a suppression capacitor connected in parallel with the communication capacitor, which acts as a mediator to shunt common mode transients to ground, preventing them from corrupting the differential signal and maintaining signal integrity across the isolation barrier.
Solution Approach 2:
The common mode suppression circuit converts the harmful common mode voltage transients into a beneficial filtering action. By providing an alternative low-impedance path to ground through the suppression capacitor, the circuit transforms the harmful transient energy into a controlled discharge path, effectively eliminating signal corruption while maintaining normal differential communication operation.
2Reliability
If common mode suppression circuitry is added to reject common mode transients, then signal integrity is improved, but device complexity increases
Solution Approach 1:
The common mode suppression function is segmented into a separate, dedicated circuit module that operates independently from the main differential communication path. This segmentation allows the suppression circuit to be designed and optimized as a standalone function, reducing the complexity burden on the core communication system while achieving improved common mode rejection through specialized circuitry.
Solution Approach 2:
The common mode suppression circuit is designed to perform multiple functions: it suppresses common mode transients, maintains differential signal integrity, and provides a controlled impedance path for transient energy dissipation. This multi-functionality reduces the need for additional separate circuits, thereby limiting the increase in overall device complexity while achieving robust common mode rejection.
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
This solution effectively reduces common mode movement by up to 20 times compared to conventional configurations, allowing communication channels to operate reliably in the presence of large common mode voltage transients, thus maintaining signal integrity.
Implementation Method 1
measuring the amount of capacitor displacement current caused by the common mode voltage movement
Implementation Method 2
The detected signal is injected into one or more signal carrying capacitors to cancel the normally detrimental displacement current simultaneously occurring in these capacitors. In some embodiments, detection and/or injection is achieved with a current mirror circuit.
Data Source
AI summary
Methods and apparatus for capacitively isolated first communication channels with common mode noise suppression. In embodiments, a driver on the first circuit transmits a data signal on the first communication channel to a receiver on the second circuit. A common mode suppression circuit on the second circuit is coupled to the receiver, output of the suppression circuit is coupled to a node between the first capacitor and the resistor network and an input is coupled to a ground of the first circuit via a second capacitor. The common mode suppression circuit is configured to detect a common mode movement signal due to a noise pulse to the second circuit on the input and generate a corresponding signal on the output to maintain a current level across the resistor network for suppressing common mode noise from the pulse.