Pseudo Dynamic Element Matching for Low-Glitch DAC Linearity
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Solution Overview
Problem
Existing digital-to-analog converters (DACs) face issues with integral nonlinearity (INL) and glitches due to dynamic element matching (DEM) methods, particularly when implementing pseudo DEM, which can fail when subsequent inputs have identical values and result in output signal glitches.
Innovation Solution
A pseudo dynamic element matching (PDEM) method that generates a priority sequence for selecting 1-bit DACs and uses a matching flag generator to determine when to change the priority sequence, ensuring at least one common cell is selected between operations and reducing glitches by reassigning priorities and generating flags for each operating period.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a randomized generator is used for dynamic element matching (DEM), then the integral nonlinearity (INL) of the DAC is reduced, but output signal glitches occur due to lack of common 1-bit DACs between subsequent outputs
Solution Approach 1:
The patent applies dynamics by making the element matching sequence adaptive rather than fixed. The pseudo-DEM method dynamically adjusts the selection of 1-bit DACs based on previous output states, ensuring continuous overlap between consecutive outputs. This dynamic adaptation eliminates glitches while maintaining INL reduction benefits.
Solution Approach 2:
The patent uses preliminary action by pre-establishing a specific sequence pattern for 1-bit DAC selection that guarantees overlap between consecutive outputs. Rather than randomizing each selection independently, the method pre-plans the sequence to ensure that at least one common 1-bit DAC exists between any two subsequent outputs, preventing glitches before they can occur.
2Object-generated harmful factors
If a pseudo DEM method is used to avoid glitches, then output signal stability is improved, but the method fails when two subsequent inputs have identical values
Solution Approach 1:
The patent resolves the identical input failure by implementing a dynamic state-tracking mechanism. When identical inputs are detected, the system dynamically adjusts the element selection based on the previous state, ensuring that the sequence continues smoothly without failure. This makes the pseudo-DEM method adaptive to all input conditions including repeated values.
Solution Approach 2:
The patent applies feedback by continuously monitoring the input sequence and adjusting the element selection accordingly. When identical inputs are detected, the feedback mechanism triggers a state update that ensures proper sequence continuation. This feedback loop prevents method failure by adapting the selection strategy based on the detected input pattern.
3Manufacturing precision
If dynamic element matching (DEM) is implemented to reduce INL, then conversion accuracy is improved, but device complexity increases due to randomized generator and decoder requirements
Solution Approach 1:
The patent replaces the complex randomized generator and decoder with a simpler pseudo-random sequence generator that uses a lookup table or pre-defined pattern. This substitution uses cheaper, simpler computational resources while achieving the same INL reduction effect, thereby reducing device complexity while maintaining conversion accuracy.
Solution Approach 2:
The patent uses copying by implementing pseudo-DEM through pre-defined sequences that replicate the statistical properties of true random sequences. Instead of generating actual random numbers requiring complex hardware, the system copies the beneficial statistical characteristics using simpler deterministic sequences, reducing device complexity while maintaining performance.
Data Source
AI summary
A method to reduce the integral non-linearity (INL) of a digital-to-analog converter (DAC) and a DAC implementing said method are disclosed. The method in this invention is a pseudo dynamic element matching (PDEM) method. Compared with a prior art, the method of this invention provides a better performance in glitch. Compared with another prior art, the method of this invention also guarantees that DEM will not fail even if the input digital code remains constant.