A mixed-signal IC for a semi-implantable hearing aid

A Hearing Aid Chip (HAC3) used in an RF-based, 2 component semi-implantable middle ear hearing device is described. The HAC3 uses a programmable gain amplifier, 2nd-order /spl Sigma/-/spl Delta/ modulator, pulse-width modulator, and class E output stage to accept an incoming audio signal and modulate it for transmission to an implanted passive receiver. The HAC3 employs a unique bias control scheme to improve signal-to-noise characteristics and reduce power consumption. The HAC3 was fabricated using a conventional 2.0 /spl mu/m CMOS process. The circuit functions as expected and test results characterizing HAC3 signal-to-noise and power conserving behavior are presented.