Design of Multi-Rate Digital Filter for Sigma-Delta Adc in Digital Microphone

Qian Peng ； Guo Cheng

《International Core Journal of Engineering》 8卷2期 (2022/02) Pp. 700-713

https://doi.org/10.6919/ICJE.202202_8(2).0092

摘要

This project design a forth-order 24-bit Sigma-Delta Analog-to-Digital Converter (ADC) with over 130 dB Signal to Noise Ratio (SNR), which is applied to audio signal processing in the digital microphone. The digital filter adopted three-order cascade structure including CIC filter, compensating filter and Half Band filter in order to eliminate noise of the audio and reduce required the circuit area and power consumption of the sigma-delta ADC. Since CIC Filter will bring signal attenuation, this project also adopts compensating filter series with the CIC filter, which can effectively enlarge the stopband attenuation and decrease passband attenuation. In addition, this project adds the Half-band filter after the compensating filter which function is double decimation. The structure of Half Band filter is used Direct-Form Symmetric FIR to reduce the amount of operation and save the multiplication and addition operation during filtering, which significantly reduce the area of the circuit and the power consumption of the multi-rate digital filter. The experimental results show that the signal-to-noise ratio of the designed digital filter reaches 132dB, the over-sampling rate is 128, attenuation of the stopband is 157dB and the attenuation of passband is 0.0001 dB.

關鍵字

Sigma-Delta ADC ； Multi-Rate Digital Filter ； Audio Signal Processing ； CIC Filter ； Compensating Filter ； Half Band Filter

參考文獻

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