Class D Amplifier Current Sensing With Replica Loops
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Solution Overview
Problem
Current solutions for sensing the output current of switching amplifiers, such as Class D amplifiers, face challenges including the need to avoid external components for efficiency, address voltage levels above the supply or below ground, provide a common voltage for sense circuits, filter ripple, and achieve high accuracy and precision, particularly in applications like micromirror systems.
Innovation Solution
The solution involves a high-precision current sensing method using replica loop circuits and a sensing circuit with a current-to-voltage converter, buffered output, and auto-zero offset technique to directly sense currents in the output bridges of switching amplifiers, eliminating the need for external components and effectively canceling ripple to accurately measure the mean load current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If external sense resistance is used for current sensing, then current measurement is achieved, but efficiency loss occurs and additional external components are required
Solution Approach 1:
The sensing circuit is fully integrated within the amplifier circuit, merging the current sensing function with the existing amplifier structure. This eliminates the need for external sense resistance and avoids the associated efficiency losses while maintaining measurement capability through replica loop circuits that sense currents internally.
Solution Approach 2:
Replica loop circuits are introduced as intermediary elements that replicate the output currents of the amplifier. These replica currents are then sensed by the sensing circuit, allowing indirect measurement of the load current without inserting external components that would cause power loss.
2Productivity
If ripple is present on bridge current, then switching operation is achieved, but measurement accuracy of mean load current deteriorates
Solution Approach 1:
The sensing circuit performs preliminary sampling of the replica currents at specific timing points within the switching cycle. By sampling at predetermined moments and holding these values, the circuit captures the mean current value before ripple effects corrupt the measurement, enabling accurate representation of the average load current.
Solution Approach 2:
The sensing circuit uses feedback mechanisms to compare and process the replica currents, extracting the mean value while rejecting ripple components. The feedback loop enables the circuit to distinguish between the useful mean current signal and the harmful ripple variations.
Data Source
AI summary
A switching amplifier, such as a Class D amplifier, includes a current sensing circuit. The current sensing circuit is formed by replica loop circuits that are selectively coupled to corresponding output inverter stages of the switching amplifier. The replica loop circuits operated to produce respective replica currents of the output currents generated by the output inverter stages. A sensing circuitry is coupled to receive the replica currents from the replica loop circuits and operates to produce an output sensing signal as a function of the respective replica currents.