Hybrid Linearized Class-BD Double Sided (LBDD) Digital Pulse Width Modulator (DPWM) for Class-BD Audio Amplifiers
DOI:
https://doi.org/10.5604/01.3001.0010.7555Keywords:
Class-D Digital Audio Amplifier, Digital Pulse Width Modulator (DPWM), Linearized Pulse Width Modulation (LPWM), Linearized Class-AD Double sided (LADD), Linearized Class-BD Double sided (LBDD), Programmable Tapped Delay Line (PTDL), Analog Delay Locked Loop (ADLL), Digital to Time Converter (DTC)Abstract
The paper presents an original architecture and implementation of 9-bit LBDD hybrid DPWM circuit for Class-BD digital audio amplifier. The input PCM signals are directly transformed into 24-bit LBDD DPWM signals and then are requanized to the 9-bit digital outputs using noise-shaping process to support high fidelity with practical values of time resolution, and finally are converted by the DTCs into the two physical trains of 1-bit PWM signals. The architecture of the proposed Class-BD hybrid DPWM circuit is composed of two Class-AD ones. The hybrid quantizer converts 6 MSB bits using counter method, based on the STM32F407xx microcontroller, while the remaining 3 LSB bits - using a method based on the Programmable Tapped Delay Line (PTDL). All necessary time waveforms are generated on the base of the internal microcontroller oscillator 168 MHz. The proposed 9-bit Class-DB DPWM circuit allows to attain SNR of 110 dB and THD about 0,2% within the audio baseband, at switching frequency of 328.1 kHz, clock frequency of 42 MHz and modulation index M = 0.95. Basic verification of algorithm and circuit operation as well as simulation and preliminary experimental results have been performed.
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