Digital Speaker Code Conversion for Lower MOSFET Switching Loss
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Solution Overview
Problem
Digital speaker systems based on multi-bit Σ-Δ modulation face high switching rates, leading to nonlinear distortion, power dissipation, and heating issues, while conventional Class-D systems fail to address unified digital coding and frequency response deviations across multiple channels.
Innovation Solution
A method and device that convert high-bit PCM signals through interpolation filtering and Σ-Δ modulation, followed by dynamic mismatch shaping and pulse width modulation, reducing switching rates and retaining harmonic suppression and deviation correction capabilities, using a code converter to align data frames and control MOSFET switching for efficient power amplification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multi-bit Σ-Δ modulation is used to reduce nonlinear distortion and improve linearity, then harmonic suppression capability is improved, but switching rate increases causing power dissipation and heating
Solution Approach 1:
The patent segments the high switching rate signal into multiple lower rate parallel channels. The multi-bit Σ-Δ modulator output is divided into several independent digital channels, each processed separately through code converters and lower switching rate power amplifiers. This segmentation maintains the benefits of multi-bit modulation while distributing the power dissipation across multiple lower-power amplifier stages.
Solution Approach 2:
The patent changes the switching rate parameter from a single high rate to multiple lower rates across parallel channels. By converting the high-rate single-channel output into lower-rate multi-channel outputs, the system achieves the same audio bandwidth coverage but with reduced switching losses in each individual power amplifier stage.
2Reliability
If high switching rate is used to maintain stability in 1-bit Σ-Δ modulation, then linearity is improved, but MOSFET generates more nonlinear distortion and heating
Solution Approach 1:
The patent segments the single high-rate channel into multiple lower-rate parallel channels. Each channel operates at a reduced switching rate that is more suitable for MOSFET performance, thereby reducing the nonlinear distortion and heating generated by each individual power amplifier while maintaining overall system stability through the combined parallel output.
Solution Approach 2:
The patent introduces dynamic element matching (DEM) to dynamically adjust and randomize the switching patterns across parallel channels. This dynamic approach distributes distortion products across the frequency spectrum rather than concentrating them, reducing audible nonlinear distortion while maintaining system stability.
3Measurement precision
If multi-bit Σ-Δ modulation is used to overcome 1-bit defects, then dynamic range is improved, but sensitivity to speaker unit inconsistency increases causing coding errors
Solution Approach 1:
The patent implements dynamic element matching (DEM) that dynamically adjusts the allocation of digital channels to speaker units based on real-time or pre-measured characteristics. This dynamic remapping compensates for inconsistencies between speaker units, ensuring that each unit receives appropriately matched channel assignments that minimize coding errors while preserving the extended dynamic range benefits of multi-bit modulation.
Solution Approach 2:
The patent incorporates feedback mechanisms through DEM that monitor and compensate for speaker unit variations. By using measured speaker characteristics to dynamically adjust channel assignments and apply mismatch shaping filters, the system feedback-corrects for manufacturing inconsistencies, maintaining coding accuracy across all speaker units while preserving the full dynamic range capability.
4Measurement precision
If high sampling rate is used in multi-bit Σ-Δ modulation, then audio quality is improved, but MOSFET switching frequency increases causing excessive heating and reduced efficiency
Solution Approach 1:
The patent segments the high sampling rate audio signal into multiple parallel channels with lower individual sampling rates. Each channel is processed by a separate power amplifier operating at a lower switching frequency, which generates less heat. The combined output of all channels reconstructs the full high-quality audio signal, achieving both high audio quality and reduced thermal output.
Solution Approach 2:
The patent changes the sampling rate parameter from a single high value to multiple lower values distributed across parallel channels. This parameter transformation maintains the overall audio fidelity by preserving the necessary bandwidth and resolution through parallel processing, while each individual channel operates at a switching frequency that generates acceptable thermal levels.
Data Source
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AI summary
A method and device for driving a digital speaker based on code conversion are provided in the invention. The method comprises the steps of: (1) converting input format; (2) performing multi-bit Σ-Δmodulation; (3) thermometer code conversion; (4) dynamic mismatch-shaping processing; (5) pulse width modulation code conversion; and (6) controlling on/off status switching of the MOSFET of a full-bridge power amplification network to drive a digital speaker load sound. The device comprises a sound source, an input format converter, a multi-bit Σ-Δ modulator, a thermometer coder, a dynamic mismatch shaper, a code converter, a multi-channel digital amplifier and a digital speaker load which are connected to each other in sequence. By means of the device and method of the invention, the switching rate of the power tube, the power dissipation and heating generated during the switching are reduced, the sound quality and efficiency of electroacoustic restoration are improved, the volume, weight and implementation cost of the system are decreased, and the level of electromagnetic radiation is reduced. Furthermore, the device and method of the invention also have excellent immunity to the frequency response deviation of multiple digital channels.