Sigma-Delta ADC Feedback Multiplexing for Accurate Battery Cell Sensing
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Solution Overview
Problem
Battery Management Systems (BMS) in electrical vehicles face challenges with high common mode voltage across battery cells, requiring external anti-aliasing RC filters that increase circuit complexity and cost, and existing continuous-time sigma-delta ADCs with multiplexing suffer from accuracy issues due to multiplexer-switch resistance and voltage transients.
Innovation Solution
A continuous-time sigma-delta ADC with multiplexers placed between feedback nodes and the amplifier stage, avoiding direct impact on the conversion equation and using chopping switches to reduce offset and 1/f noise, and incorporating a negative reference voltage for improved accuracy and robustness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If multiplexers are placed at the input of the ADC to handle multiple battery cells, then the device complexity is reduced, but the measurement precision deteriorates due to multiplexer-switch resistance and voltage transients
Solution Approach 1:
The patent introduces feedback nodes as intermediary points between the multiplexer switches and the amplifier stage. These feedback nodes allow the multiplexer switches to control the feedback path rather than the input path, eliminating the direct impact of switch resistance on the conversion equation while maintaining the ability to multiplex multiple battery cell inputs
Solution Approach 2:
Instead of placing multiplexer switches at the input to select which battery cell connects to the amplifier, the patent inverts the approach by placing the switches at the feedback path. The switches now select which feedback node connects to the amplifier inputs, effectively multiplying the input signals without introducing resistance errors into the conversion equation
2Measurement precision
If external anti-aliasing RC filters are added to handle high common mode voltage, then the measurement precision is improved, but the device complexity and cost increase
Solution Approach 1:
The patent makes the ADC circuit self-sufficient by integrating the high common mode voltage handling capability directly into the sigma-delta modulation architecture. The continuous-time modulator and feedback mechanism automatically compensate for common mode voltage variations without requiring external anti-aliasing filters, thereby maintaining measurement accuracy while reducing circuit complexity
3Device complexity
If multiplexer switches are used to reduce the number of ADCs, then the device complexity is reduced, but the electromagnetic compatibility robustness deteriorates due to voltage transients
Solution Approach 1:
The feedback nodes serve as intermediary buffer zones that isolate the amplifier stage from direct connection to multiplexer switches. This intermediary structure dampens voltage transients and electromagnetic interference before they reach the critical amplification and conversion stages, thereby improving EMC robustness while maintaining the benefits of multiplexing
Solution Approach 2:
The continuous feedback mechanism in the sigma-delta ADC actively compensates for voltage transients and electromagnetic interference introduced by the multiplexer switches. The feedback loop detects and corrects these disturbances in real-time, maintaining signal integrity and improving overall EMC robustness without requiring additional external filtering components
Data Source
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AI summary
A sigma-delta ADC comprising: a first-input-resistor connected in series between a first-input-terminal and a first-feedback-node; a second-input-resistor connected in series between a second-input-terminal and a second-feedback-node; a third-input-resistor connected in series between a third-input-terminal and a third-feedback-node; a first-multiplexer-switch connected in series between the first-feedback-node and a first-amplifier-second-input-terminal; a second-multiplexer-switch connected in series between the second-feedback-node and a first-amplifier-first-input-terminal; a third-multiplexer-switch connected in series between the third-feedback-node and the first-amplifier-second-input-terminal; a first-feedback-current-source having a first terminal and second terminal, wherein the second terminal is connected to a reference-terminal; a second-feedback-current-source having a first terminal and second terminal, wherein the second terminal is connected to the reference-terminal; a first-feedback-selection-switch connected in series between the first-feedback-node and the first terminal of the first-feedback-current-source; a second-feedback-selection-switch connected in series between the second-feedback-node and the first terminal of the second-feedback-current-source; and a third-feedback-selection-switch connected in series between the third-feedback-node and the first terminal of the first-feedback-current-source.