Programmable DEM Encoder for Smoother DAC Cell Transitions
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Solution Overview
Problem
Existing Dynamic Element Matching (DEM) techniques face limitations in achieving high-linearity due to blindness to mismatches and other sources of degradation in Digital-Controlled Oscillators (DCO) used in Digital Phase Locked Loops, resulting in data-dependent frequency errors caused by sharp transitions in DEM cell usage patterns.
Innovation Solution
A programmable DEM encoder with a binary switching tree and programmable switching blocks that allow for independent control of splitting operations and dithering, enabling a smoother transition profile by configuring switching blocks into different modes based on control signals, thereby reducing data-dependent errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing DEM techniques are used to address mismatch between DAC cells, then mismatch errors are scrambled into pseudorandom noise, but sharp transitions in the number of DEM cell transitions cause data-dependent frequency errors
Solution Approach 1:
The patent applies dynamics by making the DEM encoder programmable and adaptive. The system dynamically adjusts the number of cell transitions based on the input digital control word to maintain a consistent transition profile across different operating conditions. This prevents sharp transitions that cause data-dependent frequency errors while maintaining the mismatch scrambling benefit.
Solution Approach 2:
The patent changes the parameter of transition profile shape from sharp (triangular) to smooth (parabolic or cosine-squared). By modifying the mathematical profile of cell transitions and using dithering techniques, the system transforms the harmful sharp transitions into beneficial smooth transitions that reduce spectral leakage and data-dependent errors.
2Adaptability or versatility
If a fixed DEM encoder configuration is used, then the circuit is simple, but it cannot adapt to different mismatch patterns and operating conditions
Solution Approach 1:
The patent segments the DEM encoder into multiple independently programmable switching blocks. Each block can be individually configured to address specific mismatch patterns in different parts of the DAC circuit. This modular approach enables adaptability without requiring a complete redesign of the entire encoder, balancing complexity and versatility.
Solution Approach 2:
The patent creates a universal DEM encoder that can function in multiple modes (e.g., first-order shaping, second-order shaping, dithering modes) through programmable control. The same hardware structure adapts to different mismatch patterns and operating conditions by changing its operational mode, providing multi-functionality without proportional increases in complexity.
3Reliability
If the number of DEM cell transitions is not controlled, then the encoder operation is simple, but sharp transition profiles cause spectral leakage and degradation
Solution Approach 1:
The patent applies periodic action through dithering techniques that introduce controlled periodic variations in the cell transition patterns. This periodic dithering signal helps linearize the transition profile and reduces spectral leakage by spreading energy across multiple frequency components, improving spectral purity without requiring complex real-time control.
Solution Approach 2:
The patent implements feedback mechanisms where the DEM encoder monitors its own transition patterns and adjusts its operation to maintain optimal performance. By using feedback from the actual cell states and transition counts, the system can dynamically compensate for sharp transitions and maintain smooth profiles, reducing the need for overly complex open-loop control.
Data Source
AI summary
A dynamic element matching (DEM) encoder is provided that converts an N-bit digital codeword into a pattern of 1-bit values. The DEM encoder includes a binary switching tree that includes plurality of switching blocks interconnected between an encoder input and a plurality of encoder outputs. The plurality of switching blocks are configured to receive a plurality of first control signals such that each switching block receives a respective first control signal and is independently programmable based on the respective first control signal into a first mode or a second mode. Each switching block includes a splitting circuit programmed into the first mode or the second mode to split a digital input into two digital outputs using either both a first splitting operation and a second splitting operation that is different from the first splitting operation or the first splitting operation over the plurality of sampling intervals.