Sigma-Delta Class-D Amplifier Feedback for Load Noise Shaping
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Solution Overview
Problem
Conventional Class-D power amplifiers face issues with load modulation and lower power efficiency, particularly when using sigma delta modulators, due to switching losses at the power amplifier stage.
Innovation Solution
The implementation of a feedback loop using a feedback analog to digital converter to sense the load signal and adjust the input of the digital sigma delta modulator, ensuring that each noise-shaped output pulse contains equal energy and minimizing noise, thereby increasing power efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a sigma delta modulator is used in a Class-D power amplifier, then noise shaping function is provided and switching noise is distributed over a broader frequency range, but switching losses at the power amplifier stage reduce power efficiency
Solution Approach 1:
The patent implements a feedback loop that samples the output signal from the power amplifier stage and feeds it back to the sigma delta modulator. This feedback mechanism allows the system to detect and correct for switching losses in real-time, compensating for the energy wasted during transistor switching transitions. The feedback signal is processed through a loop filter and added to the input signal, creating an error signal that drives the modulator to optimize power delivery while maintaining noise shaping benefits.
Solution Approach 2:
The patent replaces the conventional direct connection between the sigma delta modulator and the power amplifier switching stage with a feedback-controlled system. Instead of directly controlling the switching transistors based solely on the input signal, the system uses feedback from the actual output to dynamically adjust the modulator's output, substituting the simple switching control mechanism with an intelligent feedback control loop that optimizes both noise performance and power efficiency.
2Loss of energy
If pulse width modulation is used to convert digital input signals, then power loss through driver transistors is minimized, but a relatively large noise component appears at the fixed PWM switching frequency
Solution Approach 1:
The patent transitions from fixed-frequency PWM to dynamic frequency modulation through the sigma delta modulator. Instead of operating at a constant switching frequency, the system dynamically varies the switching pattern based on the input signal amplitude and the feedback signal. This dynamic operation spreads the switching noise across a broader frequency spectrum rather than concentrating it at a single fixed frequency, while still maintaining the efficiency benefits of switching operation.
Solution Approach 2:
The patent employs periodic switching action through the sigma delta modulator, which generates a series of pulses with varying widths and densities. The modulator operates at a high fixed sampling frequency but produces output pulses that are periodically distributed based on the input signal characteristics. This periodic pulse generation, combined with noise shaping, distributes the energy of switching noise across multiple frequency components rather than concentrating it at one frequency.
Data Source
AI summary
An amplifier capable of driving an analog load is provided. The amplifier can be constructed and arranged to operate as at least one circuit selected from the group consisting of a class D amplifier, voltage regulator, audio amplifier, servo amplifier, servo control, digital control, switching power supply, and switching power amplifier. The amplifier comprises a sigma delta modulator (SDM), a pulse processing circuit, an output stage, and a feedback loop. The SDM produces a plurality of noise-shaped output pulses based upon an input signal (e.g., an analog input signal) to the amplifier and an error signal. The pulse processing circuit processes at least a portion of the plurality of noise-shaped output pulses to ensure that each of the noise-shaped output pulses in the portion contains an amount of energy that is as close as possible to the amount of energy in the other pulses. The output stage is coupled to the pulse processing circuit and has first state wherein the output stage provides analog noise-shaped output energy pulses to a load and a second state where the output energy delivered is essentially zero. The feedback loop is coupled between the output stage and the SDM. The feedback loop samples the energy provided to the load during the first state by measuring the load during the second state and generates an error signal based on the difference between the sampled portion of the noise-shaped output pulses and the input signal to the amplifier.