Class D Output Circuit With PWM/PDM Switching Frequency Control
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Solution Overview
Problem
Class D amplifiers using pulse width modulation (PWM) or pulse density modulation (PDM) suffer from distortion and noise due to deviations in carrier waveforms and variations in switching frequency, leading to suboptimal performance in output circuits.
Innovation Solution
Implementing a PWM output circuit with a square wave signal instead of sawtooth or triangular waves, and a PDM output circuit with variable reference voltages to stabilize switching frequency, along with a dual-mode output circuit that supports both PWM and PDM, using integrators, comparators, and reference generators to improve performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a sawtooth or triangular carrier wave is used in PWM modulation, then the modulation can be performed, but any deviation from an ideal waveform causes distortion in the output signal
Solution Approach 1:
The patent replaces the complex ideal sawtooth/triangular wave generator with a simple square wave generator. The square wave is a simpler, more robust waveform that can be generated easily with standard digital circuits, sacrificing the theoretical optimality of sawtooth waves for practical simplicity and reliability.
Solution Approach 2:
The patent changes the fundamental parameter of the carrier wave from sawtooth/triangular to square wave. This parameter change fundamentally alters the modulation approach but eliminates the need for complex waveform generation circuits while maintaining acceptable performance through feedback control.
2Adaptability or versatility
If PDM modulation is used with variable switching frequency, then the modulator can adapt to input signal variations, but circuit component variations cause wide switching frequency variation
Solution Approach 1:
The patent introduces feedback control mechanisms in both PWM and PDM modes. The feedback loop monitors the actual switching frequency and adjusts the modulation parameters to compensate for component variations, thereby stabilizing the switching frequency while maintaining adaptability to input signal changes.
Solution Approach 2:
The patent implements dynamic reference voltages in PDM mode that can adjust in real-time to compensate for component variations. This dynamic adjustment allows the system to maintain stable switching frequency despite variations in circuit components, while still adapting to different input signal conditions.
3Loss of energy
If class D amplifier is used for high power efficiency, then power consumption is reduced, but distortion and noise performance deteriorates due to switching mode operation
Solution Approach 1:
The patent introduces an integrator as an intermediary element between the modulator and the class D amplifier. The integrator smooths the PWM or PDM signal before it reaches the amplifier, reducing high-frequency switching artifacts and distortion while maintaining the power efficiency benefits of class D operation.
Solution Approach 2:
The patent replaces traditional linear amplifier mechanisms with a switching-based class D amplifier controlled by integrated PWM/PDM signals. This substitution achieves higher power efficiency while the feedback control and integration mechanisms compensate for the inherent distortion and noise of switching operation.
Data Source
AI summary
Output circuits using pulse width modulation (PWM) and/or pulse density modulation (PDM) are described. In one aspect, a PWM output circuit includes a PWM modulator that operates based on a square wave signal instead of a sawtooth or triangular wave signal. In another aspect, a PDM output circuit includes a PDM modulator that uses variable reference voltages to reduce variations in switching frequency. In yet another aspect, a dual-mode output circuit supports both PWM and PDM and includes a pulse modulator and a class D amplifier. The pulse modulator performs PWM on an input signal if a PWM mode is selected and performs PDM on the input signal if a PDM mode is selected. The class D amplifier receives a driver signal from the pulse modulator and generates an output signal.