Negative-Capacitance Readout Interface for Low-Noise Capacitive Sensors
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Capacitive sensors, such as microphones, are limited by the noise performance of the analog front end (AFE) and suffer from parasitic capacitances, leading to deterioration in signal-to-noise ratio (SNR).
Innovation Solution
Implementing a negative impedance converter (NIC) topology in a bootstrap configuration with a negative capacitance converter (NCC) to reduce or cancel noise associated with the main buffer amplifier, thereby improving SNR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional bootstrap techniques are used to mitigate parasitic capacitances, then signal attenuation is reduced and SNR is improved, but added noise from the buffer amplifier in the AFE further deteriorates SNR
Solution Approach 1:
The patent applies noise cancellation techniques where the buffer amplifier noise is measured during a calibration phase and then subtracted from the sensor signal during operation. This converts the harmful noise into a correctable artifact, improving the overall SNR by removing the previously detrimental buffer amplifier contribution
Solution Approach 2:
The patent performs noise characterization and calibration before actual sensing operations. The buffer amplifier noise profile is captured in advance during a calibration phase, allowing this noise to be compensated for during subsequent measurements, thereby improving SNR before the actual sensing occurs
2Measurement precision
If noise cancellation techniques are applied to reduce buffer amplifier noise, then SNR is improved, but device complexity increases due to additional calibration and compensation circuits
Solution Approach 1:
The patent combines the noise cancellation functionality with the existing bootstrap capacitor circuitry. The calibration and compensation operations are integrated into the standard readout sequence, allowing noise reduction without requiring completely separate additional hardware paths or complex external components
3Object-generated harmful factors
If negative capacitance is used to reduce AFE noise, then noise performance is improved, but stability of the readout interface may be compromised
Solution Approach 1:
The patent applies negative capacitance in a controlled, partial manner through the bootstrap configuration rather than fully compensating all parasitic effects. This partial application of negative capacitance reduces AFE noise while maintaining sufficient phase margin and stability in the feedback loop, avoiding oscillation issues that would result from complete or excessive compensation
Data Source
AI summary
Disclosed embodiments provide a self-contained topology that enables a significant noise reduction of capacitive sensor readout interfaces. For example, various embodiments can provide low noise capacitive sensor readout interfaces or analog front ends having a main buffer amplifier in a bootstrap configuration, wherein a bootstrap loop configuration comprises a negative capacitance coupled to an input of the main buffer amplifier with a negative impedance converter.