EEG Input Converter With Switched-Capacitor Voltage Boost for Low Noise
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Solution Overview
Problem
Delta-sigma A/D converters in EEG monitoring systems face challenges in minimizing noise contribution from the amplifier stage while maintaining low current consumption, which is crucial for continuous, battery-powered operation without frequent battery replacement.
Innovation Solution
The implementation of a voltage transformer upstream of the input stage with a transformation ratio greater than 1, effectively doubling the input voltage and reducing the relative noise contribution, allowing for a single-stage amplifier with reduced bias current demands and improved signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-stage amplifier is used to reduce device complexity, then the amplifier's noise sensitivity increases and current consumption rises, but this would degrade signal quality and reduce battery life
Solution Approach 1:
The patent divides the amplification function into two separate stages: a first amplifier stage that provides initial amplification of the EEG signal, and a second amplifier stage that provides additional amplification. This segmentation allows each stage to operate with moderate gain requirements, reducing noise sensitivity in each individual stage while maintaining overall high gain for the complete signal path.
Solution Approach 2:
The patent introduces an intermediary element between the two amplifier stages - a capacitor that couples the output of the first amplifier to the input of the second amplifier. This intermediary capacitor blocks DC components and low-frequency noise while passing the AC EEG signal, effectively filtering noise between stages and improving the overall signal-to-noise ratio without requiring complex filtering circuits.
2Measurement precision
If amplifier bias current is increased to reduce noise, then signal quality improves, but current consumption increases and battery life decreases
Solution Approach 1:
By dividing the total amplification into two stages, each amplifier can operate at lower bias current levels while achieving the required overall gain. The first amplifier operates with moderate current to provide initial signal boosting, and the second amplifier provides additional gain with similar moderate current requirements, resulting in lower total power consumption compared to a single high-gain amplifier stage requiring high bias current.
Solution Approach 2:
The patent replaces the traditional approach of using a single high-power amplifier with a multi-stage amplification system that uses capacitive coupling instead of direct electrical connection. This substitution allows for better noise filtering and more efficient power distribution across stages, reducing the overall current consumption while maintaining signal quality.
3Measurement precision
If a voltage transformer with transformation ratio greater than 1 is introduced upstream of the input stage, then input voltage is doubled and noise contribution is reduced, but device complexity increases
Solution Approach 1:
The patent introduces a voltage transformer as an intermediary component between the EEG electrode and the first amplifier stage. This transformer with a transformation ratio greater than 1 steps up the input voltage, which reduces the relative noise contribution of subsequent amplifier stages by effectively lowering their noise floor relative to the amplified signal level.
Solution Approach 2:
The voltage transformer changes the voltage parameter of the input signal before it enters the amplification chain. By transforming the voltage level upstream, the system achieves better noise performance without requiring the amplifiers to operate at extremely low noise levels, thereby simplifying the overall design constraints.
Data Source
AI summary
In order to minimize noise and current consumption in an EEG monitoring system (40) which can be continuously carried by a person to be monitored, an input converter (44) for an EEG monitoring system 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). A voltage transformer (IT) is placed in the input converter upstream of input stage. The transformation ratio of the voltage transformer (IT) has a transformation ratio such that it provides an output voltage larger than the input voltage, thereby multiplying the signal voltage for the input stage by a fixed factor. The voltage transformer (IT) is a switched-capacitor voltage transformer having at least two capacitors (Cx, Cy, Cz). The invention further provides a method of converting an analog signal, and an EEG monitoring system comprising the input converter (44).