Technology



Some of our products employ the novel 16 channel critical band spaced digital filter bank design [1] with natural hearing response proposed by Prof Bah Hwee Gwee and Prof Joseph Sylvester Chang from School of Electrical & Electronic Engineering, Nanyang Technological University, Singapore. Prof Gwee and Prof Chang are digital hearing instrument experts which have a number of inventions, including [3] US granted patents on circuit design. These include the low-distortion (<THD+N: – 78dB) digital filter bank, low power ([email protected]) Class-D amplifier [2] and digital signal processor [3] circuits for digital hearing instruments. They have been IEEE Distinguished Lecturers for IEEE Circuits and Systems Society.

[1] K.S. Chong, B.H. Gwee and J.S. Chang, “A 16-Channel Low Power Non-Uniform Spaced Filter Bank Core for Digital Hearing Aids,” IEEE Transactions on Circuits and Systems II: Express Briefs, vol. 53, no. 9, pp. 853-857, 2006.

16-channel filter bank

Figure 1: Block diagram of the critical band spacing spaced 16-channel filter bank

Magnitude Response of filter bank

Figure 2: The magnitude response of the critical band spaced 16-channel filter bank

[2] B.H. Gwee, J.S. Chang and V. Adrian, “A Micropower Low Distortion Digital Class D Amplifier based on an Algorithmic Pulse Width Modulator,” IEEE Transactions on Circuits and Systems I: Regular Paper, vol.52, no. 10, pp. 2007-2022, Oct 2005

Pulse Width Modulator sampling

Figure 3: Detailed illustration of the LI single-sided trailing-edge PWM sampling

Block diagram PWM Class D Amplifier

Figure 4: Block diagram of the Linear Interpolation Pulse Width Modulator for Digital Class-D amplifier with THD » 0.03%, fold-back distortion = –98.4 dB

Microphotograph Class D amplifier output stage

Figure 5:  Microphotograph of the Class D output stage

[3] Y. Shi, B.H Gwee and J. Chang, “Asynchronous DSP for Low-power Energy-efficient Embedded Systems,” Microprocessors and Microsystems, v35, n1, pp. 318–328, 13 Feb 2011.

Block diagram Asynchronous low power Digital Signal Processor

Figure 6: Block diagram of the Asynchronous Low-power (54.5 uW/[email protected] V) Digital Signal Processor for Digital Hearing Instrument

Area breakdown Asynchronous LP DSP

Figure 7: Area breakdown of the Asynchronous Low-power Digital Signal Processor