Bulk-Driven Input Transistor for Low-Noise Biopotential Acquisition
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Solution Overview
Problem
Existing input circuitries for acquiring biopotential signals face challenges in achieving compact size and low power consumption while maintaining a good signal-to-noise ratio, as they often require large input capacitors for AC coupling and contribute noise through digital-to-analog converters (DACs).
Innovation Solution
The input circuitry uses an input transistor with a digital component providing a digital signal on its bulk terminal, allowing the transistor to function as a digital-to-analog converter, eliminating the need for a separate DAC and reducing noise, and enabling a compact design with low power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If AC coupling with large input capacitors is used to filter DC electrode offset, then low frequency signals can be retained, but the circuit dimensions become very large
Solution Approach 1:
The invention changes the operating parameters by using feedback to dynamically adjust and cancel the DC electrode offset, replacing the need for large fixed capacitors with active parameter control, thereby reducing circuit dimensions while maintaining low frequency signal retention
Solution Approach 2:
The invention applies feedback by providing a signal back to the input transistor to actively cancel the DC electrode offset, enabling compact circuit design without sacrificing the ability to retain low frequency biopotential signals
2Measurement precision
If feedback through a DAC is used to cancel electrode offset, then offset compensation is achieved, but area and power consumption increase significantly
Solution Approach 1:
The invention merges the feedback mechanism with the input transistor itself, using the transistor's bulk terminal to directly implement offset cancellation without requiring a separate DAC component, thereby achieving electrode offset compensation in a compact area
Solution Approach 2:
The input transistor is made multi-functional by using its bulk terminal both for normal operation and for receiving the feedback signal to cancel electrode offset, eliminating the need for dedicated DAC hardware and reducing overall circuit area
3Measurement precision
If a separate DAC is used for offset cancellation, then electrode offset can be compensated, but noise is injected into the system affecting signal quality
Solution Approach 1:
The invention extracts the digital-to-analog conversion function from a separate noisy DAC component and integrates it directly into the input transistor's bulk terminal, eliminating the noise source while preserving the offset cancellation capability
4Extent of automation
If a separate DAC is used for analog-to-digital conversion, then signal conversion is achieved, but power consumption increases
Solution Approach 1:
The invention combines the analog-to-digital conversion function with the input transistor by utilizing the bulk terminal for digital signal reception, merging multiple functions into a single component and thereby reducing overall power consumption
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for a compact, low-power input circuitry with improved signal-to-noise ratio, as the digital signal is not summed with the analog input, maintaining input impedance and avoiding additional noise contributions.
Implementation Method 1
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
Data Source
Figure 1a~1b
Figure 1c~2
Figure 3
AI summary
An input circuitry (100; 200) for receiving an analog input signal comprises: an input transistor (102; 302a-e; 402a-f; 512a-f; 514a-f; 542a-e) configured to receive the analog input signal on a gate terminal (108; 308a-e) of the input transistor (102; 302a-e; 402a-f; 512a-f; 514a-f; 542a-e); wherein the input transistor (102; 302a-e; 402a-f; 512a-f; 514a-f; 542a-e) is connected to a digital component providing a digital signal, and wherein the input transistor (102; 302a-e; 402a-f; 512a-f; 514a-f; 542a-e) is configured to receive the digital signal on a bulk terminal (110; 310a-e) of the input transistor (102; 302a-e; 402a-f; 512a-f; 514a-f; 542a-e); wherein the input transistor (102; 302a-e; 402a-f; 512a-f; 514a-f; 542a-e) is configured to provide an output current based on the analog input signal and the digital signal, such that the input transistor (102; 302a-e; 402a-f; 512a-f; 514a-f; 542a-e) provides digital-to-analog conversion of the digital signal received on the bulk terminal (110; 310a-e).