Digital Modulation with Noise-Shaped DAC Frequency Independence
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Solution Overview
Problem
Existing digital modulation techniques require multiple asynchronous clocks and are limited by clock frequency, making it difficult to achieve independent modulation of information-bearing signals as analog signals, especially in high-performance CMOS integrated circuits.
Innovation Solution
A frequency modulator generates a modulated digital signal with an arbitrary modulation frequency, independent of the clock frequency, using a noise-shaping modulator to attenuate quantization noise through a spectral null in the noise transfer function, allowing for reduced resolution digital signals to be converted into analog signals without relying on multiple asynchronous clocks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a DAC performs signal conversions at a very high sampling rate to remove spectral replicas, then the signal-to-noise ratio is improved, but the device complexity and power consumption increase
Solution Approach 1:
The patent divides the high-speed digital signal processing into two stages: first, a noise-shaping modulator performs resolution reduction at a lower sampling rate, and second, the DAC converts the reduced-resolution signal at high speed. This segmentation allows the system to achieve high signal-to-noise ratio without requiring the entire conversion chain to operate at the highest sampling rate, thereby reducing device complexity.
Solution Approach 2:
The patent changes the resolution parameter of the digital signal before DAC conversion. By reducing the resolution of the digital signal to be converted, the patent decreases the complexity and power consumption of the DAC while maintaining the overall signal quality through noise shaping that pushes quantization noise to higher frequencies.
2Adaptability or versatility
If multiple asynchronous clocks are used to achieve multiple modulation frequencies, then the adaptability is improved, but the device complexity increases
Solution Approach 1:
The patent implements a universal modulator that can generate multiple modulation frequencies using a single clock source. The numerically controlled oscillator and noise-shaping modulator are designed to be frequency-agile, allowing the system to switch between different modulation frequencies without requiring separate asynchronous clock sources, thus reducing device complexity while maintaining adaptability.
Solution Approach 2:
The patent employs dynamic frequency adjustment through a numerically controlled oscillator that can be programmed to operate at different frequencies. This dynamic capability allows a single clock source to generate multiple modulation frequencies by changing the oscillator's operating parameters, eliminating the need for multiple fixed-frequency clock sources and reducing overall system complexity.
3Manufacturing precision
If the DAC operates at high sampling rate, then the linearity is improved, but the power consumption increases
Solution Approach 1:
The patent changes the resolution parameter of the digital signal before DAC conversion. By reducing the resolution of the digital signal to be converted, the patent decreases the power consumption of the DAC while maintaining the overall signal quality through noise shaping that pushes quantization noise to higher frequencies.
Data Source
AI summary
An arbitrary modulation frequency of a modulating signal is selected. The modulating signal is applied to an information-bearing signal, where such modulation is carried out through digital signal processing operations. The digitally modulated signal is resolution-reduced and the quantization noise introduced by such is shaped to locate a spectral null in the noise transfer function of the resolution reducing modulator at the modulation frequency. Thus, the modulation frequency can be selected independently of the clock frequency at which the resolution-reduced samples are converted to an analog signal.