A reduction of circuit size of digital direct-driven speaker architecture using segmented pulse shaping technique

Abstract

We propose a novel digital direct-driven speaker architecture using a segmented pulse shaping technique to reduce circuit size. The digital direct-driven speaker consists of a multi-bit delta-sigma modulator and a noise-shaping dynamic element matching circuit. Because the multi-bit outputs drive each of the driver circuits directly, the system can be driven at low voltage with high efficiency. However, it is necessary for the number of loudspeakers or voice coils and driver circuits to be same as the number of quantization levels. Therefore, increasing the number of quantization levels is not a straightforward process. The segmented pulse shaping technique has been proposed to increase the number of quantization levels without increasing the number of output units, thereby improving the signal-to-noise ratio and reducing out-of-band noise. However, the internal signal processing circuit size is increased. Our proposed method reduces the size of the system using a noise-shaping dynamic element matching circuit. Comparing the proposed method with the conventional method for a 33-level modulator and eight speakers, and maintaining the signal-to-noise ratio of the conventional method, the number of look-up table is reduced by 27.2% and the circuit size is reduced by 22.7%.