Class D Amplifier Mode Switching to Prevent Beat Noise
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Solution Overview
Problem
Class D amplifiers face challenges in simultaneously achieving the advantages of both self-excited and separately-excited operations, as self-excited amplifiers reduce distortion and improve efficiency but suffer from beat noise at low outputs, while separately-excited amplifiers have high switching loss and low efficiency at high outputs.
Innovation Solution
A class D amplifier design that includes an output stage, feedback circuit, integration amplifier, comparator, carrier signal generator, reference signal generator, and standard signal switch, allowing operation as a separately-excited amplifier at low outputs to prevent beat noise and switching as a self-excited amplifier at high outputs to reduce switching loss and enhance efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a self-excited class D amplifier is used, then audio performance is enhanced and efficiency is improved, but beat noise occurs at low output levels
Solution Approach 1:
The amplifier dynamically switches between self-excited and separately-excited operation modes based on the output signal level. At low output levels, it operates in separately-excited mode to eliminate beat noise. At high output levels, it switches to self-excited mode to maximize efficiency and audio performance. This dynamic mode switching resolves the contradiction by adapting the operating characteristics to the current operating conditions.
2Object-affected harmful factors
If a separately-excited class D amplifier is used, then beat noise is eliminated, but switching loss increases and efficiency decreases at high output levels
Solution Approach 1:
The amplifier transitions from static separately-excited operation to dynamic mode switching. When the output signal exceeds a threshold level, the system automatically switches to self-excited mode, which reduces switching loss and improves efficiency. This dynamic adaptation eliminates the need to operate in the inefficient separately-excited mode at high output levels, resolving the energy loss contradiction.
3Loss of energy
If self-excited operation is used at high output, then efficiency is improved, but distortion rate increases due to reduced feedback amount
Solution Approach 1:
The system dynamically adjusts the feedback amount based on the output signal level. In self-excited mode at high output levels, the feedback amount is naturally reduced, which improves efficiency. The dynamic switching allows the system to accept this increased distortion as a necessary trade-off only when the benefits of high efficiency are most needed, rather than maintaining a fixed operating mode.
Data Source
AI summary
A class D amplifier includes an output stage that performs a switching operation, a feedback circuit that generates a feedback signal based on the output signal output from the output stage, an integration amplifier that outputs an integrated value signal in response to an input signal and the feedback signal, a comparator that compares the integrated value signal with a standard signal, a driver that controls the output stage based on a signal output from the comparator, a carrier signal generator that generates a carrier signal, a reference signal generator that outputs a reference signal indicating a driving amount for a load at the output stage, and a standard signal switch that switches the standard signal to the carrier signal or a standard potential based on whether a level of the reference signal is smaller than a threshold value.