An Area-Efficient Digital Interpolation Filter Applied in Stereo Audio Sigma-Delta DAC

An area-efficient interpolation filter used in stereo audio Sigma-Delta DACs (Digital-to-Analog Converters) is presented in this paper. The 128× interpolation filter consist of three stage. The first half-band filter adopts the improved poly-phase structure, which eliminates the delay cells of even branch through sharing the delay cells with odd branch. The second 1/4 band filter gives the images caused by the first interpolation another attenuation and leaves a large design margin to the SC filter. Dual-channel multiplexing structure is applied to save the chip area through sharing the digital circuit by the left channel and right channel. The simulation and measurement results show that the designed interpolation filter meets the demand of audio applications. The design is fabricated on TSMC 0.18¿m 1.8V/3.3V 1P5M CMOS process and the digital part only takes a chip area of 0.43 mm2.