Lattice LF-81AGG-EVN

This demonstration addresses a market need for transmitting data from up to eight PDM microphones over a single data line using the I2S 8-channel aggregated format. The I²S bus is widely used to transfer PCM audio data between ICs in electronic devices. The standard I²S protocol is designed to carry only two channels (left and right) on a single data line.

The iCE40 UltraPlus 8:1 Microphone Aggregation Demo implements a custom I²S bus using the iCE40 UltraPlus FPGA. The demo uses FPGA-B on the master iCE40 UltraPlus Mobile Development Platform (MDP), along with a daughterboard equipped with eight PDM microphones as the input source. Sound captured by the microphones can be heard through the onboard audio port.

Each of the eight PDM-format data streams from the microphones is converted to PCM format using an efficient CIC filter followed by a compensation filter. The eight PCM-format data streams then enter a serializer TDM module, which outputs the serialized data in I2S 8-channel aggregated format to onboard header J30.

To drive audio to the headphone jack, the I2S 8-channel aggregated format data is sent to an I²S decoder module. This module selects either the average of all eight PCM channels or one of the eight channels, converts it to standard 2-channel I²S format, and sends it to the audio DAC amplifier. Channel selection is performed using the onboard MODE button.