DAC Frequency Synthesis with Sampling-Frequency Dithering
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Solution Overview
Problem
Modern digital-to-analog converters (DACs) in frequency synthesis systems generate analog signals with inherent alias products, which can lead to power density issues in multiple Nyquist zones, requiring inefficient filtering to achieve desired performance.
Innovation Solution
A frequency synthesis system that uses a memory to store digital control word pairs, with each pair defining a predetermined output frequency, and employs two DAC systems to generate analog sampling signals at different frequencies, allowing for efficient mitigation of power density by dithering between sampling frequencies and enabling analog output signals in higher Nyquist zones with lower sampling frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a fixed sampling frequency is used in DAC systems, then the system operation is simple, but power density of alias signals increases in multiple Nyquist zones requiring inefficient filtering
Solution Approach 1:
The patent applies dynamics by transitioning from a fixed sampling frequency to a variable sampling frequency that changes over time. The system dynamically adjusts the sampling frequency of the first DAC system between a first sampling frequency and a second sampling frequency, which directly addresses the harmful alias signals by varying the Nyquist zone boundaries, thereby reducing power density in specific zones without complicating the overall system operation through complex real-time control algorithms
Solution Approach 2:
The patent implements periodic action by cycling between different sampling frequencies in a structured manner. The system alternates between operating at a first sampling frequency and a second sampling frequency, creating periodic variations in the sampling rate that systematically distribute and reduce the power density of alias signals across different Nyquist zones over time, while maintaining predictable and manageable system behavior
2Reliability
If filtering is applied to achieve desired performance, then alias signal performance improves, but filtering complexity and operational complexity increase
Solution Approach 1:
The patent applies preliminary action by proactively reducing the power density of alias signals through variable sampling frequency modulation before the signals reach the filtering stage. By pre-processing the sampling frequency to minimize alias signal power in specific Nyquist zones, the system reduces the burden on subsequent filtering operations, thereby achieving desired alias signal performance with simpler and less complex filtering requirements
3Manufacturing precision
If higher sampling frequencies are used, then analog signal generation accuracy improves, but operational complexity and power consumption increase
Solution Approach 1:
The patent implements parameter changes by varying the sampling frequency parameter between a first sampling frequency and a second sampling frequency based on operational requirements. This allows the system to use higher sampling frequencies only when necessary for improved analog signal generation accuracy, while operating at lower sampling frequencies during other times to maintain operational efficiency and reduce power consumption, thereby optimizing the trade-off between accuracy and productivity
Data Source
AI summary
A frequency synthesis system includes a memory to store first and second digital control word pairs that each include a first and second control word. A first DAC system generates an analog sampling signal having a first sampling frequency based on a fixed clock signal and the first control word of the first pair during a first time duration having a second sampling frequency based on the first control word of the second pair during a second time duration. A second DAC system generates an analog output signal based on the second control word of the first pair and the first sampling frequency at the first time duration and based on the second control word of the second pair and the second sampling frequency at the second time duration. The analog output signal has a same predetermined output frequency at both the first and second time durations.