AC l a s s - DA m p l ifier With Pulse Code Modulated (PCM) Digital Input for Digital Hearing Aid Jinho Noh, Student Member , IEEE, Dongjun Lee , Student Member , IEEE

Abstract

Ac l a s s - Da m p l ifier with pulse code modulated (PCM) digital input is developed for a low-power digital hearing aid. A 16-bit 40-kbps PCM digital input is noise-shaped by a third-order digital sigma-delta modulator (SDM) which provides 1.5-bit dig- ital output. The 1.5-bit digital output of the digital SDM is con- verted to a three-level analog signal by a simple digital-to-analog converter (DAC) and then applied to an analog SDM. The analog SDM provides pulse density modulated (PDM) signal to drive a power switch. The PDM output is fed back to the input of the analog SDM in order to suppress the noise of the power switch. While the integrators of the analog SDM are implemented with switched-capacitor (SC) circuits for a well-de fined frequency re- sponse of the modulator loop filter , the feedback path from the power switch output is realized with a continuous-time (CT) in- tegrator for effective noise suppression. The class-D ampli fier with PCM digital input has been implemented in a standard 0.13- CMOS process. With 160- load of speaker, the maximum output power delivered to the load is 1.14-mW while the ef ficiency of the power switch is 97-%. The (SNDR) and dynamic range (DR) of the class-D ampli fier are mea- sured to be 80.6-dB and 87-dB, respectively. The class-D ampli- fier consumes 0.38-mW from a 1.2-V power supply including the driving power of the power switch.