Capacitive Sensor Signal Processing With Segmented Sigma-Delta Feedback
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Solution Overview
Problem
Capacitive sensors, such as MEMS microphones, face challenges in processing signals with high dynamic ranges due to the risk of signal distortion or clipping when exceeding the supply rails of signal processing circuits, as conventional methods often attenuate or clip the signal, which is not suitable for strict noise requirements and small sensor capacitances.
Innovation Solution
The implementation of a signal processing concept using sigma-delta modulation with segmented feedback, where higher significance bits are fed back to adjust the signal level within the operating range of the amplifier circuit, ensuring the signal remains within the desired range without additional compensation measures, thereby preventing signal distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the signal is compressed directly at the input pin of the first amplifier into the supply range, then the signal fits within the limited supply voltage and avoids clipping in active circuitry, but the signal information gets distorted by the compression
Solution Approach 1:
The patent segments the feedback signal into two separate feedback paths: one carrying higher significance bits and another carrying lower significance bits. This segmentation allows differential processing where higher significance bits are fed back to the input of the first amplifier for level shifting, while lower significance bits are fed back to the input of the first amplifier after the capacitor coupling. This resolves the contradiction by enabling precise signal level control without distortion.
Solution Approach 2:
The patent implements a segmented feedback mechanism where digital output values from downstream circuitry are fed back to the input stage. The feedback signal is split into higher significance bits (fed back to amplifier input) and lower significance bits (fed back after capacitor coupling). This feedback loop continuously adjusts the input signal level to maintain it within the amplifier's operating range, preventing distortion while preserving signal information.
2Reliability
If conventional approaches attenuate or clip the signal directly at the input pin when it exceeds the input range, then the signal level is reduced to fit the amplifier range, but valuable signal information is lost
Solution Approach 1:
The patent uses a feedback loop that takes digital output values from downstream circuitry and feeds them back to the input stage. The feedback signal is segmented into higher and lower significance bits, with higher significance bits fed back to the amplifier input to adjust the signal level. This continuous adjustment ensures the input signal remains within the amplifier's operating range without clipping or attenuation that would lose signal information.
Solution Approach 2:
The patent dynamically changes the signal level parameter by feeding back higher significance bits to adjust the input signal amplitude. Instead of fixed attenuation or clipping, the system adaptively modifies the signal level based on the actual output values, ensuring the signal stays within the amplifier range while preserving all signal information through reversible level shifting.
Data Source
AI summary
A signal processing arrangement has a signal input for connecting a capacitive sensor. An amplifier circuit is coupled between the signal input and a feedback point. A loop filter is coupled downstream to the feedback point. A quantizer is connected downstream to the loop filter and provides a multi-bit output word. The multi-bit output word consists of one or more higher significance bits and one or more lower significance bits. A first feedback path is coupled between a quantizer and the feedback point for providing a first feedback signal to the feedback point being representative of the one or more lower significance bits. A second feedback path is coupled to the quantizer for providing a second feedback signal to the signal input being representative of the one or more higher significance bits.