Sigma-Delta ADC Feedback-Node Multiplexing for Accurate Cell Sensing
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Solution Overview
Problem
Existing battery management systems face challenges with high common mode voltages in rechargeable battery stacks, requiring external anti-aliasing RC filters that increase circuit complexity and cost, and multiplexers placed before ADCs degrade conversion accuracy.
Innovation Solution
A multiplexed continuous time delta-sigma converter with multiplexers positioned between feedback nodes and amplifier inputs, using high-voltage transistors and cascode configurations to sustain high voltages, and incorporating chopping switches to reduce offset and noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If multiplexers are placed before ADC inputs to handle multiple battery cell measurements, then device complexity is reduced, but measurement precision degrades due to accuracy loss in conversion equation
Solution Approach 1:
The patent introduces feedback nodes as intermediary points between the multiplexer and ADC input. The multiplexer switches connect to feedback nodes rather than directly to ADC inputs, allowing the conversion equation to reference these stable feedback nodes instead of the switching points. This intermediary structure isolates the multiplexer switching from the precision-critical ADC conversion path, maintaining accuracy while enabling multiplexing functionality.
2Reliability
If external anti-aliasing RC filters are added to handle high common mode voltages, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent extracts the anti-aliasing filtering function from external discrete components and integrates it into the ADC's internal feedback network. By incorporating the filtering capability within the feedback path and using the feedback nodes as filtering points, the design eliminates the need for external RC filters while maintaining EMC robustness and handling high common mode voltages effectively.
3Area of stationary object
If multiplexer switches are placed directly at ADC inputs to reduce die size, then area is reduced, but measurement precision worsens due to rectification phenomena and inaccuracies
Solution Approach 1:
The feedback nodes serve as intermediary connection points that decouple the multiplexer switches from the ADC input terminals. The multiplexer switches connect to feedback nodes, which then connect to the ADC inputs through fixed resistors. This intermediary structure prevents direct switching at the ADC inputs, eliminating rectification phenomena and inaccuracies while maintaining compact die size through integrated feedback network design.
Data Source
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.