Sigma-Delta Sensor Feedback Loop for Low-Power Linearity
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Solution Overview
Problem
High-performance sensor systems with single-bit feedback require high power consumption due to large over-sampling ratios and phase-shift compensation, limiting their efficiency in battery-operated applications.
Innovation Solution
A multi-bit sigma-delta modulator with a single-bit quantizer and a digital accumulator that converts the output to a multi-bit feedback signal for a primary loop, combined with a secondary single-bit feedback loop for stability, reducing power consumption and noise shaping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If single-bit feedback is used in sensor systems, then linearity and simplicity are improved, but power consumption increases due to large over-sampling ratios
Solution Approach 1:
The feedback path is segmented into two separate loops: a single-bit feedback loop for maintaining linearity and a multi-bit feedback loop for reducing power consumption. The single-bit loop preserves the linearity advantage by feeding back only sign information, while the multi-bit loop reduces the over-sampling ratio requirement by providing more precise feedback signals, thereby lowering the power consumption associated with high-rate single-bit operation.
Solution Approach 2:
The invention transitions from a single-dimensional feedback approach (single-bit) to a two-dimensional feedback structure with distinct functional loops. The primary single-bit loop handles linearity-critical operations, while the secondary multi-bit loop handles power-efficient operations, effectively adding a dimensional aspect to the feedback architecture that allows simultaneous optimization of both linearity and power consumption.
2Measurement precision
If large over-sampling ratio is used to reduce quantization noise, then noise performance is improved, but power consumption increases due to charging and discharging of force capacitors
Solution Approach 1:
The noise reduction function is segmented between two feedback loops with different bit resolutions. The single-bit loop maintains the noise-shaping benefit while operating at a lower effective over-sampling ratio, and the multi-bit loop compensates for the reduced sampling rate by providing higher precision feedback, thereby achieving low quantization noise without the power penalty of high-rate single-bit operation.
Solution Approach 2:
The invention changes the parameter of feedback signal resolution from uniform single-bit to a combined single-bit and multi-bit structure. This parameter change allows the system to achieve equivalent or better noise performance by utilizing the multi-bit loop's higher resolution to compensate for the reduced over-sampling ratio, thereby reducing the power consumption associated with high-rate capacitor charging and discharging.
3Stability of the object's composition
If phase compensating lead-lag filter is added to guarantee stability, then system stability is improved, but power consumption increases
Solution Approach 1:
The invention extracts the phase compensation function from a separate power-consuming lead-lag filter and integrates it into the multi-bit feedback loop's digital processing path. By performing phase compensation through digital algorithms in the multi-bit loop rather than through analog filter circuits, the system achieves the required stability without the additional power consumption of dedicated analog compensation circuitry.
Solution Approach 2:
The invention substitutes analog phase compensation circuitry (lead-lag filter) with digital phase compensation implemented in the multi-bit feedback loop. This replacement of mechanical/analog systems with digital processing eliminates the power consumption associated with analog filter components while maintaining the stability-enhancing phase compensation function through software or digital signal processing algorithms.
4Use of energy by moving object
If multi-bit feedback is used instead of single-bit, then power consumption is reduced, but linearity deteriorates due to feedback signal mismatch
Solution Approach 1:
The feedback function is segmented into two specialized loops: the single-bit loop dedicated to maintaining linearity by providing precise sign information, and the multi-bit loop dedicated to reducing power consumption through lower over-sampling ratios. This segmentation allows each loop to optimize for its specific function without compromising the other, achieving both linearity and power efficiency simultaneously.
Solution Approach 2:
The single-bit feedback signal acts as an intermediary that mediates between the multi-bit feedback signal and the sensing element. The single-bit loop provides the critical linearity-determining sign information that corrects any mismatch or non-linearity introduced by the multi-bit loop, effectively using the single-bit signal as a mediator that preserves linearity while allowing the multi-bit loop to operate at lower power consumption.
Data Source
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AI summary
A modulator (100) is provided in operative engagement with a sensor element (102) having a plurality of electrodes. The modulator (100) has a single-bit quantizer (110) electrically connected to a digital accumulator (107). The accumulator (107) accumulates output information received from the single-bit quantizer (110). The accumulator (107) converts the accumulated output information received from the single-bit quantizer (110) to a multi-bit feedback signal (108) and sends the multi-bit feedback signal (109) in a primary feedback loop (108) back to the sensor element (102). The quantizer (110) sends a single-bit feedback signal (111) in a secondary feedback loop (112) back to a point before the quantizer (110).