Differential Dither ADC Quantization for Spur Reduction
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Solution Overview
Problem
High performance analog-to-digital converters (ADCs) face challenges with differential non-linearity (DNL) errors, which lead to spurs that degrade the spurious free dynamic range (SFDR), and conventional dithering methods either do not fully eliminate errors or increase the noise floor.
Innovation Solution
The system employs a pair of parallel quantizers with a dither generator providing an analog differential dither signal, applied differentially to each quantizer to perturb the quantization process, effectively reducing spurs without increasing the noise floor by using a low-cost dither source like a thermal noise diode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional dithering is applied to reduce spurs, then SFDR is improved, but the noise floor increases
Solution Approach 1:
The system divides the single quantization process into two parallel quantizers, each handling a portion of the signal with differential dither applied. This segmentation allows the spurs to be reduced through differential processing while the noise contributions from each quantizer can be managed separately, ultimately canceling out correlated noise components in the differential output.
Solution Approach 2:
The patent applies asymmetric dithering by using differential dither signals with specific statistical properties (one-sided or asymmetric probability density functions) rather than symmetric noise. This asymmetric approach allows the dither to effectively linearize the quantizer transfer function while controlling the noise floor characteristics, as the asymmetric dither concentrates energy in specific ways that reduce spurs without uniformly increasing noise across all frequencies.
2Manufacturing precision
If dither signal is added to linearize quantization, then linearity is improved, but additional noise is introduced
Solution Approach 1:
The system uses two parallel quantizers that are essentially copies of each other, with differential dither applied to both. By copying the quantization structure and applying correlated dither signals, the system achieves linearization through the differential processing of the copied outputs, while the noise introduced by dithering is canceled out in the differential combination due to the correlation between the two dither signals.
Solution Approach 2:
The patent changes the statistical parameters of the dither signal by using asymmetric probability density functions (such as exponential or uniform distributions) rather than symmetric Gaussian noise. This parameter change in the dither signal characteristics allows for effective linearization while controlling the noise floor, as the asymmetric parameters concentrate the dither energy in specific ways that reduce spurious components without uniformly increasing noise power across the spectrum.
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 reduces the size and number of spurs in the ADC output while maintaining a low noise floor, improving the linearity and resolution of the conversion process without the need for expensive or non-random dither sources.
Implementation Method 1
using a low-cost dither source like a thermal noise diode
Data Source
AI summary
An analog-to-digital conversion system includes two quantizers having a least significant bit arranged in a parallel pair. An input circuit coupled to the quantizers provides an analog input signal to the quantizers. A dither generator coupled to the quantizers provides an analog differential dither signal for perturbing quantization of the analog input signal. A combiner coupled to the quantizers adds respective outputs of the quantizers to obtain a linearized digital representation of the analog input signal.