Sense Amplifier Feedback Circuit for Low-Noise Physiological Signals
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Solution Overview
Problem
Existing sense amplifiers struggle to maintain accurate sensing of very small biological signals (less than about 1 mV) in the presence of large common mode signals (greater than about 10 mV) and significant noise, especially in implantable medical devices, while consuming minimal power (less than about 5 μW).
Innovation Solution
A sense amplifier with common mode feedback circuitry and synchronized sensing times is implemented, featuring three amplification stages providing up to 40,000 total amplification with a bandwidth of 500 Hz and noise of about 1 μArms between 0.1 Hz and 15 Hz, along with high-pass filter stages and programmable gain amplifiers to mitigate the effects of task signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing sense amplifiers are used to sense small biological signals, then sensing capability is provided, but accurate sensing of very small signals (less than 1 mV) in the presence of large common mode signals (greater than 10 mV) and noise deteriorates
Solution Approach 1:
The patent implements common mode feedback circuitry that continuously monitors the common mode voltage at the inputs of the differential amplifier and adjusts the common mode level at the outputs to counteract large common mode signals. This feedback mechanism enables the amplifier to maintain accurate differential signal sensing even when subjected to large common mode voltages greater than 10 mV, directly resolving the contradiction between sensing accuracy and common mode interference.
2Measurement precision
If amplification is increased to enhance small signal detection, then sensitivity improves, but noise amplification and susceptibility to common mode signals worsens
Solution Approach 1:
The patent divides the amplification function into three distinct stages: a first amplification stage with gain of 10-100, a second amplification stage with gain of 10-100, and a third amplification stage with gain of 10-100, providing total amplification of 1,000-1,000,000. Each stage is designed with specific bandwidth filtering (0.1 Hz to 15 Hz) and noise performance characteristics. This segmentation allows the system to achieve high overall sensitivity while controlling noise amplification at each individual stage, and the distributed architecture enables independent optimization of each stage for different aspects of signal conditioning.
3Use of energy by moving object
If power consumption is reduced for implantable device operation, then energy efficiency improves, but signal sensing capability and noise rejection deteriorates
Solution Approach 1:
The patent implements synchronized sensing times that are coordinated with task signal delivery, blanking out or reducing amplification during periods when task signals are being delivered. The sense amplifier operates in synchronized intervals, actively sensing during designated time windows and entering low-power states during task signal delivery. This periodic operation enables the implantable device to maintain adequate signal sensing capability during critical measurement periods while significantly reducing average power consumption overall.
4Measurement precision
If bandwidth is increased to capture more signal frequencies, then signal capture capability improves, but noise reception and susceptibility to interference worsens
Solution Approach 1:
The patent implements a fixed bandwidth of 0.1 Hz to 15 Hz for the sense amplifier stages, which is specifically optimized for capturing physiological signals such as cardiac and nerve activity. This bandwidth parameter is carefully selected to pass the frequency range where biological signals of interest occur while blocking higher frequency noise and interference. The consistent bandwidth across all three amplification stages ensures that signal capture capability is maintained for relevant physiological frequencies while noise reception is minimized by excluding frequencies outside the physiological signal range.
Data Source
AI summary
A device includes a sensor signal input node and a high-pass filter stage. The high-pass filter stage includes an operational amplifier and a feedback integrator. The operational amplifier includes an input node coupled to the sensor signal input node. The feedback integrator is coupled between an output node of the operational amplifier and the input node of the operational amplifier to set a high-pass pole frequency of the high-pass filter stage.