Signal Isolator Circuit for Common-Mode Transient Suppression
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Common mode transient signals interfere with circuit operation, overwhelming the dynamic range for differential input signals and posing challenges in signal isolator applications with multi-ground domains.
Innovation Solution
A closed-loop common mode transient suppression circuit with a class AB high bandwidth buffer that sinks and sources fast transient currents, separating common mode and differential impedances to allocate maximum dynamic range to differential signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a purely passive filtering approach is used to suppress common mode signals, then the common mode signals can be attenuated, but the common mode and differential paths share the same impedance which limits the available dynamic range for differential signals
Solution Approach 1:
The patent segments the common mode and differential signal paths by introducing separate impedance paths. A dedicated common mode feedback path with impedance Zcm is created alongside the differential signal path with impedance Zdiff. This segmentation allows independent optimization of each path's dynamic range and prevents the common mode signal from consuming the dynamic range allocated for differential signals.
Solution Approach 2:
The patent introduces a feedback mechanism as an intermediary element. The common mode feedback circuit senses the common mode voltage and generates a compensating signal that is injected back into the input path. This intermediary feedback path actively counteracts common mode signals without interfering with the differential signal path, thereby preserving the full dynamic range for differential signals while suppressing common mode interference.
2Reliability
If the common mode signal amplitude is much larger than the differential signal, then common mode transient immunity is challenged, but allocating dynamic range to process the common mode signal reduces the dynamic range available for the differential signal
Solution Approach 1:
The patent implements segmentation by creating separate feedback paths for common mode and differential modes. The common mode feedback path uses impedance Zcm while the differential path uses impedance Zdiff. This allows the system to handle large common mode signals through the dedicated feedback path without affecting the dynamic range allocation for differential signals, thereby improving CMTI while preserving signal processing capability.
Solution Approach 2:
The patent changes the impedance parameters by introducing separate impedance values for common mode (Zcm) and differential (Zdiff) paths. By adjusting these impedance parameters independently, the system can optimize the common mode rejection ratio without compromising the dynamic range for differential signals. The feedback mechanism dynamically adjusts the common mode voltage level, effectively handling large common mode transients while maintaining adequate dynamic range for differential signal processing.
3Reliability
If a closed-loop feedback circuit is used to suppress common mode transients, then common mode transient immunity is improved, but the circuit complexity increases
Solution Approach 1:
The patent uses a feedback circuit as an intermediary mechanism to suppress common mode transients. The feedback path senses the common mode voltage and generates a compensating signal that counteracts the transient without requiring complete redesign of the main signal path. This intermediary approach improves CMTI while adding only the necessary feedback components rather than fundamentally complicating the entire circuit topology.
Solution Approach 2:
The patent improves CMTI by changing key circuit parameters through the feedback mechanism. By adjusting the feedback impedance (Zcm) and gain parameters, the system achieves enhanced common mode transient immunity. The feedback circuit modifies the effective input impedance and common mode rejection characteristics without requiring complex active compensation circuits or multiple operational amplifiers, thus improving reliability with controlled complexity increase.
Data Source
AI summary
Methods and apparatus for a signal isolator that mitigates the effects of CMTI strikes. In embodiments, a first die comprises a transmit module and the first die has a first voltage domain; and a second die comprises a receive module including a receive amplifier configured to receive from the transmit module a transmit signal that includes a differential signal and a common mode current. The second die may have a second voltage domain with the first and second die being separated by an isolation barrier. In embodiment, the receive amplifier includes a differential amplifier to receive the differential input signal from the transmit module; and a common mode module configured to sense the common mode current and sink or source the common mode current and minimize changes to an input impedance of the receive amplifier.