Dual-Path Digital PWM Amplifier for Flat Frequency Response
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Solution Overview
Problem
Conventional digital amplifiers for audio signals fail to flatten the frequency characteristic of output voltage, leading to variations in gain between low-frequency and high-frequency bands, and are prone to distortion due to unsynchronized power supply voltages and A/D converter saturation.
Innovation Solution
A digital amplifier configuration that includes a digital PWM generator, multiple amplifier circuits, low-pass filters, attenuators, and a voltage supply unit to maintain a constant voltage ratio between amplifier circuits, extracting and adjusting error signals to flatten the frequency characteristic and suppress distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single amplifier circuit is used to amplify the digital PWM signal, then the device complexity is reduced, but the frequency characteristic of the output voltage cannot be flattened
Solution Approach 1:
The amplifier circuit is divided into two separate amplifier circuits (first amplifier circuit and second amplifier circuit) with different voltage configurations. The first amplifier circuit operates with a second voltage (larger absolute value) and the second amplifier circuit operates with a third voltage (smaller absolute value). This segmentation allows each circuit to handle different frequency ranges effectively, enabling flat frequency characteristics across the entire audio band while maintaining manageable device complexity through modular design.
2Manufacturing precision
If error feedback is implemented to reduce distortion, then the manufacturing precision improves, but the device complexity increases
Solution Approach 1:
An error feedback mechanism is implemented where the output signal is fed back through the second amplifier circuit and second low-pass filter to generate an error signal. This error signal is then subtracted from the input signal to correct distortion. The feedback path uses the second amplifier circuit with smaller voltage to reduce the impact of power supply voltage variations on the feedback signal, thereby improving distortion reduction performance while keeping the feedback circuit complexity manageable.
Solution Approach 2:
The second amplifier circuit and second low-pass filter serve as an intermediary in the feedback path. This intermediary configuration allows the error signal to be extracted with reduced sensitivity to power supply voltage fluctuations, acting as a buffer between the output and the error detection mechanism. This intermediary approach improves manufacturing precision by stabilizing the feedback signal while adding only moderate complexity to the overall circuit.
3Adaptability or versatility
If unsynchronized power supply voltages are used in amplifier circuits, then the adaptability improves, but distortion increases
Solution Approach 1:
Different voltage synchronization requirements are applied to different parts of the circuit. The first amplifier circuit uses a second voltage that is synchronized with the A/D converter clock, ensuring high precision for the main signal path. The second amplifier circuit uses a third voltage with smaller absolute value that may have different synchronization characteristics, suitable for the feedback and error detection path. This local quality approach allows each circuit section to operate with optimal voltage characteristics for its specific function, maintaining adaptability while reducing overall distortion.
Data Source
AI summary
A digital amplifier includes a digital PWM generator, a first amplifier circuit, a first low-pass filter, a second amplifier circuit, a second low-pass filter, an attenuator, an error extractor, an adder, and a voltage supply unit. The first amplifier circuit amplifies a digital PWM signal at a second voltage. The first low-pass filter extracts a low-frequency band voltage signal from the amplified digital PWM signal, and outputs the extracted voltage signal to a load. The second amplifier circuit amplifies the generated digital PWM signal at a third voltage. The error extractor extracts an error signal. The adder adds a digital error signal whose feedback gain is adjusted to a digital audio signal. The voltage supply unit generates the third voltage that has a voltage value of a predetermined ratio to a voltage value of the second voltage, and supplies the third voltage to the second amplifier circuit.