Switched-Mode Amplifier Pre-Modulation for Low Harmonic Distortion
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Solution Overview
Problem
Conventional switched-mode amplifiers face limitations in achieving improved harmonic distortion performance and high attenuation of residual unwanted ripple signals without compromising stability margins or requiring complex high-order filters.
Innovation Solution
The implementation of a switched-mode amplifier architecture that includes a loop filter, a pre-modulation block for uniform pulse-width modulation, and double sampling by the pre-modulation block in conjunction with the PWM block, which attenuates residual clock signals using transmission zero notches, eliminating the need for an output filter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If high-order filters are employed to provide additional attenuation of the carrier signal, then attenuation of residual carrier signals is improved, but device complexity increases and stability margins are reduced
Solution Approach 1:
The patent changes the parameters of the loop filter by employing a higher order sigma-delta modulator (e.g., 3rd order or higher) which inherently provides greater attenuation of residual carrier signals at the PWM frequency without requiring separate high-order output filters. This modifies the filtering characteristics through parameter adjustment of the modulator order.
Solution Approach 2:
The patent merges the loop filter and output filter functions into a single integrated loop filter structure. The loop filter simultaneously performs error signal filtering and carrier signal attenuation, eliminating the need for separate high-order output filters and reducing overall device complexity.
2Manufacturing precision
If high in-band open loop gain is achieved, then distortion and noise performance are improved, but attenuation of PWM carrier frequency is reduced
Solution Approach 1:
The patent changes the order of the sigma-delta modulator to achieve a configuration where high in-band open loop gain and high carrier frequency attenuation can coexist. By increasing the modulator order, the system gains both improved distortion performance through higher open loop gain and enhanced carrier attenuation through the inherent noise shaping of the higher order modulator.
Solution Approach 2:
The patent employs global negative feedback around the entire amplifier including the power stage, which minimizes switching artifacts and improves distortion performance. The feedback mechanism works in conjunction with the higher order modulator to simultaneously achieve high open loop gain and effective carrier frequency attenuation.
3Loss of energy
If conventional switched mode amplifier topology is used, then efficiency is achieved through switched-mode output devices, but distortion performance is limited by finite attenuation of residual carrier signals
Solution Approach 1:
The patent maintains the efficient switched-mode operation of output devices while improving distortion performance by changing the modulator order parameter. The higher order sigma-delta modulator provides better attenuation of residual carrier signals, thereby reducing intermodulation distortion while preserving the high efficiency benefits of switched-mode power delivery.
Data Source
AI summary
Systems and methods for switched-mode amplifiers having improved harmonic distortion are disclosed. High order in-band filtering is enabled without undue trade-off of distortion due to intermodulation/aliasing. A pre-modulation block is introduced, deployed between a loop filter block and a pulse-width modulation block, performing uniform pulse-width modulation. The pre-modulation block attenuates/removes amplitude dependent high frequency ripples before pulse-width modulation. The pre-modulation block in conjunction with the pulse-width modulation block performs double sampling of the input signals.