@conference{ogata2006digital, title = {Digital-Driven Piezoelectric Speaker using Multi-Bit Delta-Sigma Modulation}, author = {Ogata, Katsuya and Soga, Tsuyoshi and Ueno, Hajime and Yasuda, Akira}, booktitle = {Audio Engineering Society Convention 121}, month = {Oct}, year = {2006}, url = {https://www.aes.org/e-lib/browse.cfm?elib=13777} }