Chopper-Stabilized Sensor Readout Circuitry for High-Impedance Electrodes
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Solution Overview
Problem
Existing sensor readout circuitry with delta-sigma modulators face challenges in achieving high input impedance while minimizing flicker noise, particularly when dealing with high-impedance sensors like small electrodes, which degrades signal amplitude and introduces noise.
Innovation Solution
A sensor readout circuitry using a delta-sigma modulator with a transconductance amplifier incorporating a flipped voltage follower and chopper stabilization, where a chopping loop is formed with input transistors and current sources to filter out flicker noise, and bootstrapping circuitry is used to boost input impedance without additional power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a transconductance amplifier is added to achieve high input impedance, then input impedance is improved, but flicker noise increases
Solution Approach 1:
The harmful flicker noise generated by the transconductance amplifier is extracted and removed through the chopping loop mechanism. The periodic switching of the choppers modulates the noise to a higher frequency band where it can be filtered out, effectively separating the useful signal from the harmful noise component.
Solution Approach 2:
The chopping loop acts as an intermediary mechanism between the transconductance amplifier and the output. It introduces periodic switching elements (choppers) that mediate the signal path, allowing the amplifier to provide high input impedance while the chopping action transfers the signal to a frequency range where flicker noise can be eliminated.
2Area of stationary object
If circuitry size is reduced for wearable/implantable applications, then device compactness is improved, but signal acquisition capability deteriorates
Solution Approach 1:
The delta-sigma modulator is designed to perform multiple functions within a single integrated circuit block. It simultaneously provides analog-to-digital conversion, signal filtering, and high-input impedance buffering through its transconductance amplifier stage, eliminating the need for separate discrete circuits and reducing overall device size while maintaining signal acquisition capability.
Solution Approach 2:
The patent merges the transconductance amplifier, chopping loop, and delta-sigma modulation functionality into a single integrated readout circuitry. This consolidation combines multiple signal processing functions that would traditionally require separate components, achieving compact circuitry suitable for wearable and implantable applications without sacrificing measurement precision.
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
The solution provides high input impedance and improved noise performance, enabling small-sized sensor readout circuitry suitable for high-impedance sensors like small electrodes, reducing inconvenience and invasiveness, especially in biopotential signal sensing applications.
Implementation Method 1
the transconductance amplifier comprises a first chopper between an input terminal for receiving the analog sensor input signal and an input transistor of the pair of input transistors for upmodulating the analog sensor input signal
Implementation Method 2
a feedback signal from a digital-to-analog converter (DAC) of the delta-sigma modulator is received across the source degeneration resistor such that subtraction between the analog sensor input signal and the feedback signal is performed in the transconductance amplifier
Data Source
AI summary
A sensor readout circuitry comprises: a delta-sigma modulator; an input stage for receiving an analog sensor input signal, wherein a transconductance amplifier and a current mirror incorporate a flipped voltage follower, wherein a feedback signal from a digital-to-analog converter of the delta-sigma modulator is received such that subtraction between the analog sensor input signal and the feedback signal is performed in the transconductance amplifier and mirrored by the current mirror to an output of the input stage; wherein the transconductance amplifier comprises a first, second and third chopper, whereby a chopping loop between the first, second and third choppers is formed including an input transistor and current sources and whereby the analog sensor input signal is in baseband at a node in which the feedback signal is received.