ADC Charge Injection Dithering for Low-Frequency Oversampling
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Solution Overview
Problem
Conventional embedded analog-to-digital converters (ADCs) face challenges in achieving high resolution due to cost constraints and non-linearity issues, where increasing resolution exponentially increases cost, and oversampling alone may not improve integral non-linearity, limiting the Effective Number of Bits (ENOB).
Innovation Solution
A low-cost charge injection mechanism is used to inject dither noise into the ADC input, reducing quantization noise and allowing for oversampling of low-frequency signals, and to characterize ADC non-linearity errors for digital correction, thereby improving ENOB.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If dither noise is added using a fast noise source and active/passive component circuit, then quantization noise is reduced, but device complexity and cost increase
Solution Approach 1:
The patent replaces expensive, complex active dithering circuits with a simple capacitive injection mechanism that uses inexpensive capacitors to generate dither noise. This approach achieves the same quantization noise reduction without requiring fast noise sources or complex active components, effectively using cheap passive elements instead of expensive active ones.
Solution Approach 2:
The patent substitutes an electrical dithering mechanism (capacitive charge injection) for a traditional electrical noise generation circuit. By using capacitor charge/discharge cycles to generate dither noise instead of relying on thermal noise from resistors or active noise sources, the system achieves dithering functionality with simpler, more integrated-friendly components.
2Measurement precision
If ADC resolution is increased, then measurement precision improves, but cost increases exponentially
Solution Approach 1:
The patent applies dither noise and performs oversampling before the final conversion process. By pre-processing the signal with dithering and multiple sampling, the system achieves effective resolution improvement without requiring the ADC hardware itself to have higher native resolution, thus avoiding exponential cost increases while still achieving the desired measurement precision.
Solution Approach 2:
The patent changes the operating parameters of the ADC system by introducing dither noise and implementing oversampling. This transforms the effective resolution through signal processing parameters rather than hardware resolution parameters, allowing resolution improvement without proportionally increasing manufacturing cost.
3Measurement precision
If oversampling is used on low frequency signals, then effective resolution improves, but quantization noise reduction is limited by ADC non-linearity
Solution Approach 1:
The patent applies dither noise to the ADC input before oversampling to counteract the effects of quantization and non-linearity. This preliminary action of adding controlled noise prevents the signal from settling into fixed quantization patterns caused by non-linearity, allowing oversampling to effectively average out errors and improve resolution despite ADC imperfections.
Data Source
AI summary
A low-cost charge injection mechanism may enable oversampling to be used on low frequency signals by injecting dither noise into the ADC input. The dither noise can reduce the quantization noise allowing even direct current (DC) signals to be oversampled correctly. A low-cost charge injection mechanism can also be used to improve the ENOB by characterizing the ADC and digitally correcting the converted signal for non-linearity errors such as INL. Reducing INL errors may also allow a higher degree of oversampling to be used to further improve the ENOB.