VCO-Based ADC Feedback Prediction for High Linearity
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Solution Overview
Problem
Existing analog to digital converters (ADCs) face challenges in achieving high dynamic range and linearity while tolerating motion artifacts and electrode offsets, particularly in wearable sensors and IoT devices.
Innovation Solution
A high-resolution VCO-based ADC circuit with a predictor and DAC in the feedback path, which uses correlation between successive samples to predict input values and minimize distortion, thereby reducing the voltage swing seen by the VCO.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional VCO-based ADCs are used, then frequency domain operation and intrinsic noise shaping are achieved, but non-linear V-F conversion and low input impedance occur
Solution Approach 1:
The predictor performs preliminary estimation of the input signal by evaluating correlation between successive samples and generating a predicted input sample before the actual quantization occurs. This preliminary action reduces the dynamic range of the VCO input signal, allowing the VCO to operate in a more linear region and thereby improving linearity while maintaining noise shaping capabilities
2Manufacturing precision
If voltage swing reduction is achieved through prediction, then linearity improves, but additional circuit complexity is introduced
Solution Approach 1:
The predictor acts as an intermediary component between the input signal and the VCO quantizer. It processes the digital output and generates a predicted input sample that is fed back through the DAC to subtract from the original input. This intermediary structure reduces the voltage swing at the VCO input, improving linearity without requiring fundamental changes to the VCO-based architecture
Solution Approach 2:
The invention implements a feedback mechanism where the predicted input sample is converted to analog through the DAC and subtracted from the original input signal. This feedback loop continuously adjusts the VCO input to minimize distortion, improving linearity while using a structured approach that balances complexity and performance
3Measurement precision
If high dynamic range is achieved to capture small biopotentials, then sensitivity improves, but susceptibility to motion artifacts and electrode offsets increases
Solution Approach 1:
The predictor performs preliminary estimation of the input signal by evaluating correlation between successive samples. This preliminary action effectively predicts and removes the majority of the signal content, including motion artifacts and electrode offsets, before the VCO quantization process. As a result, the VCO processes only the residual signal containing the small biopotentials of interest, enabling high dynamic range operation with improved tolerance to artifacts
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 achieves a state-of-the-art total harmonic distortion (THD) of −105 dB, with significant reduction in voltage swing and improved linearity, enabling high-performance sensor readout applications.
Implementation Method 1
voltage-controlled oscillator (VCO)-based quantizer that receives a voltage input signal to be quantized and provides a digital output
Data Source
AI summary
An analog to digital conversion (ADC) circuit includes a voltage-controlled oscillator (VCO)-based quantizer that receives a voltage input signal to be quantized and provides a digital output. A predictor samples the digital output, evaluates correlation between successive samples, and predicts a predicted input sample from the correlation to minimize voltage-to-frequency transfer of the VCO. A feedback loop L1 with a digital to analog converter (DAC) receives the predicted input sample, converts it and subtracts it from the voltage input signal. A feedback loop L2 adds the predicted sample to the digital output.