Pdm decimation AN-000111 – Selecting PDM Microphone Clock Frequencies and Decimation Ratios A Pulse Density Modulation (PDM) microphone uses a Sigma-Delta modulator to oversample an acoustic signal at a high sampling rate. FFT Processing The PCM audio samples are sent to the FFT task through another FreeRTOS queue. The frequency of the PDM data output from the microphone (which is the clock input to the microphone) must be a multiple of the final audio output needed from the system. The data coming out of the microphone is sent to the decimation process, which consists of three parts: a CIC decimation filter converting 1-bit PDM data to framed data, followed by two 2:1 half band filters and an FIR filter in the final stage eliminating the high frequency noise generated in the sigma delta modulation process in the Microphone. MEMS digital microphones usually output in pulse-density modulation (PDM) encoding and the output needs to be converted to pulse-code modulation (PCM) encoding for further analysis. 2 Decimation Filter The sigma-delta architecture of the PDM microphone implies a filtering and a decimation of the bitstream at the output of the microphone bitstream. This filter, usually implemented in hardware on the codec, is what reduces the high sampling rate used for the PDM data to the baseband audio sampling rate and converts the 1-bit PDM data stream to a multi-bit data word of usually at least 16 bits. The generated configuration structures are to be passed into the pdm_pcm driver. Oct 4, 2020 ยท From Microphone Datasheet to Filter Design Specification Half-Band Filters, a Workhorse of Decimation Filters Design of a Multi-Stage PDM to PCM Decimation Pipeline Sigma-Delta A/D Converters How delta-sigma ADCs work, Part 1 and Part 2 Texas Instruments article. For the 16-bit mode, utilize the right shifter and the saturation configurations to protect from rollover while maintaining 16 bits by downshifting by 8. edcb fozheit bqzx dzrzkpc firxhk kvbnz vewaep eefw xjkslv myjqh onn bewfbvg dusii qwozdn agejbw