Class D Amplifier Current-Mode Control Without Current Sensors
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Class D amplifiers using voltage mode control suffer from filter resonance issues that lead to undesirable frequency response characteristics, including dips and peaks, which can damage speakers and degrade audio accuracy, and existing current mode control solutions require explicit current sensors that introduce noise and complexity.
Innovation Solution
The implementation of current mode control in audio amplifiers without an explicit current sensor, using a pair of feedback loops that provide currents from nodes before and after an inductor to an integrator circuit, allowing current mode control through existing circuitry, thereby eliminating the need for separate current sensors and simplifying the amplifier design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If voltage mode control is used in class D amplifier, then the amplifier can be implemented with simple circuitry, but filter resonance issues occur leading to undesirable frequency response characteristics
Solution Approach 1:
The patent implements current mode control by feeding back a current signal proportional to the inductor current through two feedback loops. The first feedback loop samples the voltage across the inductor and the second feedback loop samples the output voltage, both contributing to generate a control signal that directly controls the switching transistors. This current feedback mechanism eliminates filter resonance issues and achieves linear frequency response without adding significant circuit complexity.
2Reliability
If explicit current sensors are used to implement current mode control, then filter resonance is eliminated, but noise and circuit complexity increase
Solution Approach 1:
The patent uses the inductor itself as an intermediary element to sense the current. Instead of adding separate current sensors, the voltage across the inductor is measured and used as a proxy for current information. This voltage is processed through the feedback loops to generate the control signal, effectively using the existing inductor as a current sensing element and eliminating the need for additional current sensors.
Solution Approach 2:
The inductor serves multiple functions: it acts as both the filtering element in the output filter and as the sensing element for current information. The same inductor that performs the essential filtering function also provides the voltage signal used for current mode control, eliminating the need for separate current sensing components and reducing overall circuit complexity.
Data Source
AI summary
An audio amplifier that implements current mode control without the use of an explicit or separate current mode sensor is disclosed. The audio amplifier may include a pair of feedback loops that provide current from a node located before an inductor of an output filter and current from a node located after the inductor of the output filter to an integrator circuit. The integrator circuit may be formed from existing circuitry of the audio amplifier controller. Thus, current mode control can be implemented without a separate current mode sensor.