Dither Lookup Table Reduces Spurs in Digital-to-Time Converter
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Solution Overview
Problem
Direct digital synthesizer (DDS) circuits face challenges with spurious emissions due to both quantization and mismatch errors, with existing dithering methods only effectively reducing quantization error contributions, leaving mismatch error contributions unmitigated, making it difficult to achieve low enough spurious emissions for practical radio transceiver applications.
Innovation Solution
A new dithering approach that utilizes a lookup table to map 2k equally spaced delays to 2k values, combining with a dither source to control the statistics of the quantizer output, effectively reducing both quantization and mismatch errors by adjusting the average delay to approach ideal timing, thereby reducing spurious emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional dithering is used to eliminate quantization error contribution to spurs, then quantization error is reduced, but mismatch error contribution to spurs remains unmitigated
Solution Approach 1:
The patent segments the delay values into multiple groups and applies different dithering strategies to each group. By dividing the delay range and applying targeted dithering to specific segments, the system addresses both quantization error in some segments and mismatch error in others, resolving the contradiction between reducing quantization error while mitigating mismatch error
Solution Approach 2:
The patent changes the dithering parameters dynamically based on the delay value. By adjusting dither amplitude and frequency according to the specific delay segment being processed, the system optimizes performance for both quantization error reduction and mismatch error mitigation across different operating conditions
2Measurement precision
If dither noise is added to reduce quantization error, then spectral purity improves in some areas, but noise is spread across the spectrum
Solution Approach 1:
The patent applies dithering with locally optimized characteristics to different portions of the spectrum. By tailoring the dithering parameters to specific frequency regions or delay segments, the system improves spectral purity in critical areas while minimizing broadband noise generation in less critical regions
Solution Approach 2:
The patent employs periodic dithering sequences rather than continuous random noise. By using periodic patterns with specific frequencies and durations, the system achieves spectral purity improvements while concentrating noise energy into predictable, manageable patterns rather than spreading it uniformly across the spectrum
Data Source
AI summary
A direct digital synthesizer (DDS) (300) that uses a system for reducing spurious emissions in a digital-to-time converter (DTC) (317). The DDS (300) includes one or more dither sources (307) and a random access memory (RAM) (305). The RAM (305) utilizes a look-up table for storing delay error values by using an output of the look-up table which is combined with the dither source (307) to compensate unequal unit delay values in the DTC (317).