Class D Amplifier Ripple Correction Using Digital Supply Feedback
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Solution Overview
Problem
Class D amplifiers suffer from 0 dB power supply rejection, causing power supply ripple to directly affect the output, which is audible and increases total harmonic distortion, particularly in battery-powered applications with stringent power and size constraints.
Innovation Solution
A digital correction loop that samples the supply voltage with ripple, using an ADC, averaging filter, and digital divider to calculate a correction factor, which is fed back into the amplifier chain to adjust gain and improve power supply rejection and reduce harmonic distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional Class D amplifiers are used, then high efficiency and compact size are achieved, but power supply ripple is directly transferred to the output with 0 dB power supply rejection
Solution Approach 1:
The patent implements a feedback mechanism where the power supply voltage is monitored and used to dynamically adjust the gain of the amplifier stages. The correction factor calculated from the power supply voltage samples is applied to the audio signal path, creating a closed-loop system that compensates for power supply variations and reduces ripple transfer to the output.
Solution Approach 2:
The patent performs preliminary correction by sampling the power supply voltage and calculating the correction factor before the audio signal is fully processed. The gain adjustment is prepared in advance based on power supply conditions, allowing the system to preemptively compensate for ripple effects before they significantly impact the output quality.
2Object-affected harmful factors
If analog feedback loop is implemented to improve power supply rejection, then PSR is enhanced, but power consumption increases and chip area is occupied
Solution Approach 1:
The patent replaces the conventional analog feedback loop with a digital correction approach. Instead of using analog circuits to monitor and correct power supply variations, the system uses digital signal processing techniques including ADC conversion, digital filtering, and computational algorithms to achieve the same PSR improvement with lower power consumption and reduced hardware complexity.
Solution Approach 2:
The patent changes the operating parameters of the amplifier by dynamically adjusting gain values based on power supply voltage measurements. By modifying the gain parameter in response to power supply conditions, the system achieves improved power supply rejection without requiring additional analog feedback infrastructure, thereby reducing power consumption and chip area requirements.
3Object-affected harmful factors
If gain is adjusted to compensate for power supply ripple, then power supply rejection is improved, but noise for small signals may increase
Solution Approach 1:
The patent applies partial correction by using an averaging filter that processes multiple power supply voltage samples before calculating the correction factor. This approach applies only the necessary amount of gain adjustment to compensate for ripple while filtering out excessive variations, thereby maintaining power supply rejection improvement without over-correcting and introducing noise to small signals.
Data Source
AI summary
An amplifier includes an amplifier chain and a digital correction loop coupled to the amplifier chain. The digital correction loop includes an analog-to-digital (ADC) converter, an averaging filter, and a digital divider. The digital correction loop is configured to generate a correction factor based on ripple or noise in a supply voltage. The amplifier chain is configured to apply the correction factor to an input signal.