Class D Amplifier Power Stage Scaling for Low Idle Dissipation
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Solution Overview
Problem
Class D amplifiers face a design challenge in finding a balance between maximum audio output power and minimum idle dissipation, as increasing the size of power transistors to minimize on-resistance leads to increased idle dissipation and reduced efficiency.
Innovation Solution
A dynamic power stage control system that adjusts the size of the amplification stage based on the input signal strength, using a comparator and power stage control circuit to enable only the necessary number of power stages, with a decaying signal to prevent premature disabling and phase mismatch issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the size of the power transistor is increased to minimize on-resistance, then the signal amplification capability is improved, but the idle dissipation of the power transistor stage is increased
Solution Approach 1:
The patent applies dynamics by making the power transistor size adjustable rather than fixed. The amplifier can dynamically switch between different power transistor sizes based on operating conditions, allowing optimal balance between signal amplification capability and idle dissipation at different signal levels
Solution Approach 2:
The patent changes the physical parameter of power transistor size by providing multiple power transistor stages with different sizes. The system can select appropriate transistor sizes based on input signal characteristics, thereby optimizing the trade-off between amplification power and energy loss
2Power
If the size of the power transistor is increased to minimize on-resistance, then the maximum audio output power is improved, but the efficiency of the class D amplifier is reduced
Solution Approach 1:
The amplifier dynamically adjusts which power transistor stages are active based on the required output power level. For low-power operation, only smaller transistors are used to maintain high efficiency. For high-power demands, larger transistors are activated to provide sufficient current capability, thus optimizing efficiency across the entire power range
Solution Approach 2:
The power amplifier is segmented into multiple parallel power transistor stages with different sizes. This segmentation allows the system to activate only the necessary number and size of transistors based on the current operating conditions, preventing unnecessary energy consumption while maintaining the capability for high power output when needed
Data Source
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AI summary
Disclosed is a class D amplifier (300) comprising a modulation stage (110) having a first input (112) for receiving an input signal (212) and an output for producing a modulated version (216) of the input signal; a plurality of power stages (130), each power stage being responsive to said modulation stage and comprising a first switch (132) and a second switch (134) coupled in series between a first voltage source (140) and a second voltage source (150), each power stage comprising an output node (136) between the first switch and the second switch; and a power stage control circuit (340) for measuring the input signal level and enabling a selected number of the power stages as a function of the measured input signal level. A method for controlling such a class D amplifier is also disclosed.