Class D Amplifier Load Measurement Through LC Filter Feedback
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for measuring load in class D amplifiers, particularly in high-frequency applications, face challenges in accurately determining load impedance due to the presence of LC demodulator filters, which make it difficult to measure load voltage and current correspondence, especially in fully differential topologies with feedback before the filter.
Innovation Solution
A measuring system that senses AC output current magnitude and phase both differentially and in common mode, allowing for effective AC load and LC network impedance measurement even in configurations where single-ended driving is not possible, by using a common-mode control circuit and performing ripple current measurements to evaluate inductance before determining load impedance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If LC demodulator filters are used in class D amplifiers, then high-frequency performance is improved, but load measurement accuracy deteriorates
Solution Approach 1:
The patent segments the measurement process into two distinct modes: common-mode measurement for high-frequency ripple current and differential-mode measurement for low-frequency load current. This segmentation allows each measurement mode to be optimized for its specific frequency range, resolving the contradiction between high-frequency performance and measurement accuracy by preventing frequency-dependent measurement errors from affecting both measurement types equally.
Solution Approach 2:
The patent introduces a common-mode control circuit as an intermediary that senses high-frequency ripple current separately from the differential load current. This intermediary measurement path allows the system to extract load information without being corrupted by the LC filter's frequency-dependent behavior, thereby maintaining measurement accuracy while preserving high-frequency performance.
2Reliability
If fully differential topology with feedback before LC filter is used, then amplifier performance is improved, but load diagnostics capability deteriorates
Solution Approach 1:
The patent inverts the conventional measurement approach by measuring common-mode signals (ripple current) instead of directly measuring differential load current through the feedback path. This inversion bypasses the obstacle created by the feedback-before-filter topology, enabling load diagnostics in fully differential configurations that were previously impossible with conventional measurement methods.
Solution Approach 2:
The patent creates a universal measurement system that can handle both fully differential topologies with feedback before the LC filter and traditional single-ended configurations. The common-mode control circuit serves multiple functions: it measures high-frequency ripple current, provides load diagnostics, and works across different amplifier topologies, making the measurement system universally applicable regardless of the specific feedback configuration.
3Ease of operation
If external shunt resistors are used for current sensing, then measurement simplicity is improved, but system complexity and invasiveness deteriorates
Solution Approach 1:
The patent enables the amplifier to measure its own load current using existing internal circuitry (the common-mode control circuit and ripple current sensing) rather than requiring external shunt resistors. This self-service measurement approach eliminates the need for additional external components, reducing system complexity and avoiding the invasiveness of external current sensing while maintaining measurement capability.
Data Source
AI summary
A method can be used to measure a load driven by a switching amplifier having a differential input, an LC output demodulator filter and a feedback network between the amplifier output and the differential input. The amplifier is AC driven in a differential and in a common mode by applying a common. The feedback network provides feedback towards the differential input from downstream the LC demodulator filter by computing the impedance of the load as a function of the differential mode output current and the common mode output current. The feedback network provides feedback towards the differential input from upstream the LC demodulator filter by measuring the impedance value of the inductor of the LC demodulator filter, and computing the impedance of the load as a function of the differential mode output current, the common mode output current and the impedance value of the inductor of the LC demodulator filter.