Band-Limited PWM Signal Generation for High Dynamic Range
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Solution Overview
Problem
Pulse-width modulated systems face challenges in generating high dynamic range signals due to jitter, inaccuracies in edge transitions, noise folding, and aliasing, which degrade the dynamic range and introduce out-of-band noise, especially when upconverted to RF frequencies.
Innovation Solution
A method and system that calculate a finite number of basis functions representing a pulse-width modulated signal, specifically using the first k Fourier harmonics to create a band-limited signal, reducing aliasing and noise floor, and implementing this in a digital domain to avoid process dependencies and nonlinearities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a PWM signal is generated using conventional switching methods, then power efficiency is improved, but aliasing and noise folding occur that degrade dynamic range
Solution Approach 1:
The patent applies noise shaping before the PWM modulation stage to pre-process the signal and push quantization noise out of the band of interest. This preliminary action prevents noise folding and aliasing from degrading the dynamic range, while the subsequent PWM switching maintains power efficiency.
Solution Approach 2:
The patent introduces an intermediary noise-shaping filter between the input signal and PWM modulator. This intermediary component shapes the noise spectrum before modulation, preventing out-of-band noise from folding back into the signal band and degrading dynamic range.
2Object-affected harmful factors
If high-order filtering is used to attenuate aliasing and out-of-band noise, then adjacent band interference is reduced, but device complexity increases
Solution Approach 1:
The patent performs noise shaping in advance to pre-suppress out-of-band noise and aliasing components before they are generated by PWM modulation. This preliminary suppression reduces the burden on subsequent filters, allowing simpler filtering to achieve the same level of adjacent band interference rejection.
Solution Approach 2:
The patent converts the harmful quantization noise generated by digital-to-analog conversion into a beneficial shaped noise spectrum that is pushed out of the band of interest. This noise shaping technique transforms what would be harmful aliasing and noise folding into controlled out-of-band energy that is easier to filter.
3Measurement precision
If PWM frequency is increased to reduce quantization noise, then dynamic range is improved, but power consumption increases
Solution Approach 1:
The patent applies noise shaping before PWM modulation to pre-suppress quantization noise, achieving high dynamic range without requiring excessively high PWM frequencies. This preliminary noise suppression allows the system to operate at lower switching frequencies, reducing power consumption while maintaining dynamic range performance.
Data Source
Figure 1a~1b
Figure 1c~1d
Figure 1e~2a
AI summary
In an embodiment, a method of generating a pulse-width modulated signal from an input signal includes calculating a finite number of basis functions of a first pulse-width modulated signal based on the input signal, and forming an electronic output based on the calculated finite number of basis functions.