Bulk-Driven Input Circuitry for Low-Power Biopotential Sensing
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Solution Overview
Problem
Existing input circuitries for acquiring biopotential signals face challenges in achieving a compact design with low power consumption while maintaining a good signal-to-noise ratio, particularly due to the need for large input capacitors to filter out DC electrode offset and the power and area consumption of digital-to-analog converters (DACs).
Innovation Solution
The input circuitry employs an input transistor with a digital component providing a digital signal to the bulk terminal, enabling the input transistor to function as a digital-to-analog converter (DAC) without the need for a separate DAC component. This approach reduces noise contribution and preserves input impedance, allowing for a compact and power-efficient design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If large input capacitors are used to filter out DC electrode offset, then the quality of acquiring small amplitude biopotential signals is improved, but the dimensions of circuitry become very large
Solution Approach 1:
The patent extracts the DC electrode offset from the analog signal path by providing it as a digital signal to the bulk terminal, separating the offset cancellation function from the analog input stage and eliminating the need for large input capacitors
Solution Approach 2:
The patent replaces the mechanical/analog approach of using large input capacitors for DC offset filtering with a digital approach, where the bulk DAC provides digital feedback to the bulk terminal to cancel DC offset, thereby reducing circuit dimensions
2Reliability
If feedback is provided through a separate DAC to cancel electrode offset, then the quality of signal acquisition is improved, but area and power consumption increase
Solution Approach 1:
The patent merges the input transistor with the digital-to-analog conversion function by utilizing the bulk terminal of the input transistor as the DAC output, eliminating the need for a separate DAC component and reducing power consumption
Solution Approach 2:
The input transistor serves multiple functions: it acts as the input device for the analog signal, provides digital-to-analog conversion through its bulk terminal, and enables DC offset cancellation, thereby eliminating the need for separate dedicated components
3Reliability
If feedback is provided through a separate DAC to cancel electrode offset, then the quality of signal acquisition is improved, but device complexity and area increase
Solution Approach 1:
The patent combines the input transistor and DAC functionality into a single integrated structure, where the bulk terminal of the input transistor directly receives the digital feedback signal, simplifying the overall circuit architecture
Solution Approach 2:
The input transistor is designed to perform multiple functions including signal amplification, digital-to-analog conversion via the bulk terminal, and DC offset cancellation, reducing the number of separate components needed
Data Source
AI summary
An input circuitry for receiving an analog input signal comprises: an input transistor configured to receive the analog input signal on a gate terminal of the input transistor wherein the input transistor is connected to a digital component providing a digital signal, and wherein the input transistor is configured to receive the digital signal on a bulk terminal of the input transistor; wherein the input transistor is configured to provide an output current based on the analog input signal and the digital signal, such that the input transistor provides digital-to-analog conversion of the digital signal received on the bulk terminal.