Hearing Aid Delta-Sigma Input Converter With Switched-Capacitor Transformers
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Solution Overview
Problem
Delta-sigma A/D converters in hearing aids face challenges in minimizing noise contribution from the amplifier stage while maintaining low current consumption, which is crucial for prolonged battery life, as reducing current consumption increases noise sensitivity.
Innovation Solution
Implementing voltage transformers to scale down the noise contribution from the amplifier stage by transforming the input and feedback signals, allowing for reduced amplification and lower noise levels without increasing current demand, using an equivalent of ideal transformers in a practical delta-sigma A/D converter design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the bias current for the amplifier in the A/D converter is reduced to lower power consumption, then current consumption decreases and battery life extends, but shot noise increases due to the stochastic phenomena caused by reduced current flow
Solution Approach 1:
The amplifier stage is divided into multiple parallel amplifier elements (first amplifier element and second amplifier element) that operate simultaneously. This segmentation allows the total bias current to be distributed across multiple elements, reducing the current through each individual element and thereby reducing shot noise from each element, while maintaining the required total amplification gain.
2Measurement precision
If the amplification gain is increased to improve signal level, then the signal-to-noise ratio improves, but the current consumption increases due to higher bias current requirements
Solution Approach 1:
The amplification function is segmented across multiple parallel amplifier elements, each providing partial gain. The combined effect of multiple elements with moderate individual gains achieves the required total amplification without requiring any single element to operate at high current levels, thus maintaining good signal-to-noise ratio while keeping current consumption low.
Solution Approach 2:
Multiple amplifier elements are merged in parallel configuration, where their individual amplification contributions combine to achieve the required total gain. This merging allows the system to achieve high overall amplification through cooperative action of multiple low-current elements rather than relying on a single high-current element.
Data Source
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AI summary
In order to minimize noise and current consumption in a hearing aid, an input converter comprising a first voltage transformer and an analog-to-digital converter of the delta- sigma type for a hearing aid is devised. The analog-to-digital converter of the input converter has an input stage, an output stage, and a feedback loop, and the input stage comprises an amplifier (QA) and an integrator (RLF). The first voltage transformer (IT) has a transformation ratio such that it provides an output voltage larger than the input voltage and is placed in the input converter upstream of the input stage. A second voltage transformer (OT) having a transformation ratio such that it provides an output voltage larger than the input voltage, is optionally placed in the feedback loop of the converter. The voltage transformers (IT, OT) are switched-capacitor voltage transformers, each transformer (IT, OT) having at least two capacitors (Ca, Cb, Cc, Cd). The invention further provides a method of converting an analog signal.