Class-D Amplifier Test Circuit Using PWM Loop as ΣΔ ADC
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Solution Overview
Problem
High costs and limited space on test handlers for industrial testing of Class-D amplifiers due to the need for external hardware like low-pass filters and ADCs, and noisy environments complicating sensitive measurements during testing.
Innovation Solution
An integrated circuit with a Class-D amplifier that can switch between operational and test modes, reconfiguring the PWM control loop as a ΣΔ ADC by adding a sampler, eliminating the need for external ADCs and mitigating noise effects by integrating a digital representation of the input signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If external hardware (low-pass filter and ADC) is used for audio measurements during testing, then measurement capability is improved, but testing cost and space requirements increase
Solution Approach 1:
The patent combines the ADC functionality with the existing PWM control loop components (comparator, integrators, feedback network) to create an integrated ΣΔ ADC. This merging eliminates the need for separate external ADC hardware during testing, reducing both cost and space while maintaining audio measurement capability up to 5kHz
Solution Approach 2:
The PWM control loop components are designed to serve dual purposes: their primary function for Class-D amplifier operation and a secondary function as ΣΔ ADC components for audio measurements during testing. This multi-functionality allows the same hardware to perform both amplification control and audio quality testing without requiring separate dedicated test equipment
2Measurement precision
If external ADC is used for audio measurements, then measurement accuracy is improved, but noise from the test environment affects sensitive measurements
Solution Approach 1:
The patent uses the existing PWM control loop components (integrators and feedback network) as intermediaries to process and condition the measurement signal. These components act as built-in noise filtering and signal conditioning elements that protect the measurement process from environmental noise interference while maintaining measurement accuracy
Solution Approach 2:
The system performs its own audio measurements using its existing operational components without requiring separate external measurement hardware. The PWM control loop components serve themselves by simultaneously performing their amplification control function and acting as the measurement system, thereby immune to external test environment noise
Data Source
Figure 1~2
Figure 3~4
AI summary
An integrated circuit comprising a Class-D amplifier for amplifying an input signal at an input terminal is disclosed. The Class-D amplifier is switchable between an operational mode, in which a comparator (4) is directly coupled to an output stage (5), and a test mode, in which the comparator (4) is coupled to the output stage (5) via a sampler (15) and the output stage (5) is coupled to the input terminal via a feedback network, whereby a digital representation of the input signal is available at an output of the sampler (15).