Clock Dithering in Audio D/A Converters for EMI Reduction
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Solution Overview
Problem
Audio D/A converters face challenges in reducing electromagnetic interference due to clock harmonics, which can worsen signal quality and increase circuit complexity when using traditional dithering processes, especially when the clock signal is sourced through a Phase Locked Loop (PLL).
Innovation Solution
A clock dithering process and apparatus that employs a dither generator with a periodic ultrasonic modulating wave, integrated with a DSP and PLLs to generate a dithered output signal, ensuring the dither frequency is equal to or a multiple of the oversampling frequency, thereby reducing electromagnetic interference without degrading audio signal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If traditional dithering process is used to reduce electromagnetic interference, then electromagnetic interference is reduced, but circuit complexity increases and linearity performance deteriorates
Solution Approach 1:
The patent changes the frequency parameter of the clock signal by applying dithering modulation, spreading the clock harmonics energy across a wider frequency spectrum. This reduces the amplitude of individual peaks while maintaining the overall signal integrity, thereby reducing electromagnetic interference without requiring additional circuit components.
Solution Approach 2:
The patent employs periodic dithering modulation applied to the clock signal, creating a time-varying frequency spectrum that spreads electromagnetic energy over time. This periodic modulation reduces peak emissions while maintaining continuous operation, achieving EMI reduction through temporal distribution of energy.
2Object-affected harmful factors
If dithering process is used to reduce electromagnetic interference, then electromagnetic interference is reduced, but dynamic range deteriorates
Solution Approach 1:
The patent carefully controls the modulation depth and frequency of the dithering signal to achieve EMI reduction while staying within the linear operating range of the D/A converter. By optimizing these parameters, the system reduces electromagnetic interference without pushing the converter into non-linear regions that would degrade dynamic range.
3Object-affected harmful factors
If clock signal is modulated with ultrasonic frequency, then electromagnetic interference is reduced, but signal quality may deteriorate due to jitter
Solution Approach 1:
The patent uses periodic ultrasonic frequency modulation of the clock signal to spread electromagnetic energy across a broader spectrum. The periodic nature of this modulation creates a predictable pattern that reduces peak emissions while the high frequency of the ultrasonic carrier ensures the modulation is inaudible and does not directly affect audio signal quality.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively reduces electromagnetic interference while maintaining high system performance and simplicity, ensuring the audio output is not distorted, thus meeting stringent radio-frequency interference standards.
Implementation Method 1
A clock dithering process and apparatus that employs a dither generator with a periodic ultrasonic modulating wave, integrated with a DSP and PLLs to generate a dithered output signal
Data Source
AI summary
A process and apparatus for generating an output signal whose frequency varies according to a modulation scheme, the process including the steps of providing a dither generator for receiving a first input signal representative of a clock frequency and for generating, according to the modulation scheme, a dithered output signal representative of the first signal at a dithered frequency; providing a DSP for receiving the following input signals: the signal at the dithered frequency and a second signal representative of a clock frequency, the DSP adapted to generate a processed output signal representative of the maximum frequency of the second signal; wherein the modulation scheme has a periodic ultrasonic modulating wave.