Continuous-Time Sigma-Delta ADC for High Common-Mode Voltage
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Solution Overview
Problem
Existing sigma-delta analogue to digital converters (ADCs) face challenges in handling high common-mode voltages typically found in battery management systems (BMS) for electric vehicles, leading to increased board-level integration complexity and cost due to the need for external anti-aliasing RC filters in discrete-time approaches, and unsuitability of common-mode regulation circuits for very high voltage inputs.
Innovation Solution
A continuous-time sigma-delta ADC design that performs high voltage to low voltage level shifting directly within the first-amplifier-stage, using cascoded transistors and integration capacitors to sustain high voltages while operating in the low voltage domain, eliminating the need for external filters and reducing complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If discrete-time sigma-delta ADC approach is used, then conversion accuracy is improved, but external anti-aliasing RC filters are required increasing board-level integration complexity and cost
Solution Approach 1:
The patent combines the anti-aliasing filter function with the sigma-delta ADC by implementing a continuous-time architecture where the modulator itself performs the filtering function. The continuous-time nature of the modulator inherently provides anti-aliasing without requiring separate external RC filters, thus merging two functions into one integrated solution.
Solution Approach 2:
The patent employs a continuous-time sigma-delta modulator that operates continuously rather than in discrete sampling intervals. This continuous operation allows the system to process high common-mode voltages directly without requiring discrete-time sampling and external filtering, maintaining continuous useful action throughout the conversion process.
2Reliability
If common-mode regulation circuits are used for high voltage inputs, then voltage regulation is improved, but the circuits become unsuitable for very high voltage inputs
Solution Approach 1:
The patent changes the operating parameters of the sigma-delta modulator to accommodate very high common-mode voltages. By designing the modulator to operate directly with high common-mode voltage inputs and adjusting the integrator and quantizer parameters accordingly, the system achieves both voltage regulation and adaptability to very high voltage inputs without requiring separate regulation circuits.
3Measurement precision
If external anti-aliasing RC filters are added, then signal accuracy is improved, but integration cost increases
Solution Approach 1:
The patent merges the anti-aliasing filtering function into the continuous-time sigma-delta modulator architecture itself. The modulator's continuous operation and internal feedback mechanism inherently provide the necessary anti-aliasing filtering, eliminating the need for separate external RC filter components and reducing overall integration cost while maintaining signal accuracy.
Data Source
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AI summary
A sigma-delta ADC comprising: a first-input-terminal configured to receive a first-high-voltage-analogue-input-signal; a second-input-terminal configured to receive a second-high-voltage-analogue-input-signal; an output-terminal configured to provide an output-digital-signal, wherein the output-digital-signal is representative of the difference between the first-high-voltage-analogue-input-signal and the second-high-voltage-analogue-input-signal. The sigma-delta ADC also includes a feedback-current-block, which comprises: a first-feedback-transistor having a conduction channel; a second-feedback-transistor having a conduction channel; a first-feedback-switch; a second-feedback-switch; a first-feedback-current-source; and a second-feedback-current-source.