Multiphase PWM Modulator for Class D Audio Amplifiers
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Solution Overview
Problem
Existing class D audio amplifiers face challenges in generating accurate and well-matched multiphase pulse width modulated signals due to variations in analog triangular waveforms produced by separate generators, leading to inefficiencies and performance degradation in power efficiency, flying capacitor stability, and audio performance.
Innovation Solution
A multiphase pulse width modulator comprising N+1 analog triangular waveform generators and comparators, along with a crosspoint switch controller, produces highly accurate and well-matched pulse width modulated signals by generating rising, falling, and idle segments, ensuring even distribution of mismatch errors across signals through interleaved time segments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If separate analog triangular waveform generators are used to produce multiphase PWM signals, then device complexity is reduced, but manufacturing precision and signal matching deteriorate due to component variations
Solution Approach 1:
The patent merges N+1 separately generated pulse width modulated phase signals into N accurate multiphase PWM output signals using a crosspoint switch. This combining approach allows the system to use simple separate waveform generators while achieving high precision in the final output signals through the intelligent switching and interleaving process.
Solution Approach 2:
The crosspoint switch acts as an intermediary device that receives N+1 phase signals from separate generators and transforms them into N accurate multiphase PWM signals. This mediator component enables the system to overcome the precision limitations of separate generators by redistributing and recombining their outputs in a controlled manner.
2Manufacturing precision
If N+1 phase signals are generated to improve PWM accuracy, then signal matching improves, but device complexity increases due to additional crosspoint switching components
Solution Approach 1:
The patent segments the generation of PWM signals into N+1 separate phase signals that are then processed individually by the crosspoint switch. This segmentation allows each phase to be generated independently with simple circuitry, while the crosspoint switch handles the complex task of combining them into accurate multiphase outputs, distributing the complexity across manageable segments.
Solution Approach 2:
The system changes the parameter of phase number from N to N+1 in the intermediate stage. By generating N+1 phase signals instead of directly generating N signals, the system creates redundancy that allows the crosspoint switch to select and combine signals in a way that cancels out mismatches, improving overall accuracy despite the additional component.
3Device complexity
If traditional AD or BD modulation is used, then device complexity is low, but power efficiency deteriorates due to large ripple current in output inductor
Solution Approach 1:
The patent implements multilevel PWM modulation with N mutually phase shifted signals that periodically switch across the loudspeaker load. This periodic multiphase switching pattern distributes the current ripple across multiple phases and time segments, reducing the peak ripple current in the output inductor compared to traditional single-phase AD or BD modulation, thereby improving power efficiency.
Data Source
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AI summary
The present invention relates to a multiphase pulse width modulator producing N mutually phase shifted pulse width modulated signals having a predetermined cycle time. The multiphase pulse width modulator is particularly well-suited for application in class D audio amplifiers. The multiphase pulse width modulator comprises N +1 analog triangular waveform generators configured to produce respective N+1 mutually phase shifted analog triangular waveforms. The multiphase pulse width modulator further comprises N+1 comparators each comprising a first input operatively coupled to respective ones of the N+1 mutually phase shifted analog triangular waveforms and a second input coupled to an audio signal to generate at least N+1 mutually phase shifted pulse width modulated phase signals. A crosspoint or matrix switch comprises N+1 input terminals, coupled to respective ones of the N+1 mutually phase shifted pulse width modulated phase signals, and N output terminals configured for supplying respective ones of the N mutually phase shifted pulse width modulated signals. A crosspoint switch controller of the cross-point switch is configured to selectively connect each of the N+1 input terminals to each output terminal of the N output terminals for a duration of the predetermined cycle time in a predetermined time sequence to simultaneously generate the N mutually phase shifted pulse width modulated signals such that each of the signals comprises interleaved time segments of the N+1 mutually phase shifted pulse width modulated phase signals; N being a positive integer larger than or equal to 2.