Bridge-Tied Class D Audio Amplifier for Full-Voltage Output
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Solution Overview
Problem
Class D audio amplifiers are limited in output signal amplitude to half of the supply voltage, restricting their power output and ability to suppress electromagnetic interference (EMI) and achieve superior transient response for higher power applications.
Innovation Solution
The implementation of a 'bridge-tied-load' (BTL) audio amplifier configuration with a single or dual comparator setup, incorporating additional feedback loops to ensure continuous switching cycles and opposite output polarities between stages, allowing output signals to reach full supply voltage and improving transient response and EMI suppression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a single-ended Class D amplifier configuration is used, then the amplifier achieves power efficiency and simplified control, but the output signal amplitude is limited to half of the supply voltage
Solution Approach 1:
The amplifier is divided into two independent output stages (positive and negative) that operate in a push-pull manner. Each stage has its own switching network and output terminal, allowing the load to be connected between the two outputs. This segmentation enables the output voltage to swing from nearly 0V to nearly Vcc, doubling the output amplitude compared to single-ended configurations.
Solution Approach 2:
The invention transitions from a single-ended output topology to a differential output topology by adding a second output stage. This dimensional change in the circuit architecture allows both outputs to contribute to the voltage across the load, effectively doubling the available output voltage swing and power delivery capability.
2Device complexity
If the output signal amplitude is limited to half of the supply voltage, then the amplifier maintains simplicity, but the ability to suppress EMI and achieve superior transient response is compromised
Solution Approach 1:
The patent implements feedback networks that connect the output terminals back to the input stages. This feedback mechanism allows the amplifier to maintain better control over the output signal, improving transient response and reducing electromagnetic interference by actively correcting deviations and suppressing noise.
3Power
If a bridge-tied-load configuration is implemented, then the output signal can reach full supply voltage, but the circuit complexity increases
Solution Approach 1:
The invention merges two single-ended amplifier stages into a unified bridge-tied-load configuration where both stages share common power supply rails and control logic. This merging approach achieves full supply voltage output capability while consolidating control functions and reducing the number of independent components compared to two separate amplifiers.
Data Source
AI summary
A Class D audio amplifier with output signals capable of being as high as the amplifier's supply voltage. The audio amplifier contains a comparator, a positive output stage, and a negative output stage. The output signal from the positive output stage and the output signal from the negative output stage have opposite polarities and are connected to the comparator's negative and positive input terminals respectively. The Class D audio amplifier has superior transient response, and in turn, provides good sound quality and low THD. The resulting variable switching frequencies also help to alleviate EMI problems.