Receive Amplifier Circuit for Common-Mode Transient Immunity
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Solution Overview
Problem
Common mode transient signals interfere with circuit operation, overwhelming the dynamic range for differential input signals, especially in signal isolator applications where common mode transients can be an order of magnitude greater than differential signals.
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 the differential signal path.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a purely passive filtering approach is used to handle common mode signals, then the common mode and differential paths share the same impedance, but the maximum differential dynamic range cannot be allocated to the signal of interest in the presence of large common mode signals
Solution Approach 1:
The patent divides the common mode and differential signal paths into separate impedance networks. The common mode path has its own dedicated impedance elements (common mode resistors and capacitors), while the differential path has separate impedance elements (differential resistors and capacitors). This segmentation allows independent optimization of each path, enabling the differential path to maintain maximum dynamic range while the common mode path handles transient suppression.
Solution Approach 2:
The patent extracts the common mode signal handling function from the shared impedance network and creates a separate common mode processing path. By taking out the common mode current sensing and suppression circuitry as a distinct functional block, the differential signal path is freed from having to share impedance resources, allowing full allocation of differential dynamic range to the signal of interest.
2Object-affected harmful factors
If the common mode signal amplitude is much larger than the differential signal, then the dynamic range is overwhelmed by common mode signals, but the differential signal cannot be properly processed
Solution Approach 1:
The patent introduces a common mode sensing amplifier as an intermediary element that detects the common mode voltage and generates a compensating signal. This intermediary circuit processes the large common mode signal separately and uses feedback to cancel its effect on the differential input, thereby protecting the differential signal detection from being overwhelmed while maintaining measurement precision.
Solution Approach 2:
The patent implements feedback circuits in both the common mode and differential paths. The common mode feedback loop senses the common mode voltage and adjusts the common mode impedance to suppress transients. The differential feedback loop maintains the integrity of the differential signal. These feedback mechanisms allow the system to handle large common mode signals without compromising differential signal detection accuracy.
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.