X-Powers, a company better known to supply PMIC “companion” chip for Allwinner processors, also made some audio chips including AC108 is a chip specifically designed for microphone arrays with support for 4 microphones, and an I2C + I2S output interface to the host processor. Microphone arrays are particularly useful for smart speakers, and especially hot word detection (voice activity detection) as single microphone setups like I use with Orange Pi Zero, may have trouble detecting hot words like “OK Google” in noisy environments (music playing, alarm ringing…).
X-Powers AC108 specifications:
- 108 dB dynamic range (A-weighted) @ 0 dB boost gain
- -90 dB THD+N (total harmonic distortion plus noise) @ 0 dB boost gain
- 4x programmable boost amplifiers with 0dB to 45dB in 3dB step
- ADC sample rates supported – 8kHz,12kHz,16kHz, 22.05kHz, 24kHz, 32kHz, 44.1kHz, 48kHz,96kHz
- Analog mixer and digital mixer in record data path
- 4x fully differential microphone inputs: MIC1P/N ~MIC4P/N configurable as pseudo-differential, single-ended mode, or digital MIC data pin
- 4x low noise mic bias outputs: MIC1_BIAS~MIC4_BIAS with a 1.5V to 4V programmable bias voltage
- 2x DMIC SCLK output @ 1M~3.25M
- Two I2S data output configurable as
- I2S/PCM format using 1 pin to output 2 channel data of 1 device.
- I2S/PCM format using 2 pins to output 4 channel data of 1 device.
- TDM format using 1 pin to output 4 even 16 channel data of 4 devices.
- Encoding format using 1 pin to output 4 even 16 channel data of 4 devices.
- DPLL support a wide input for 6-/12-MHz, 6.144-/12.288-MHz, 5.6448-/11.2896-MHz, 13MHz, and 19.2MHz.
- Control Interface – I2C / TWI from 100 kHz up to 400 kHz
- Integrated LDO allowing single 3.3V supply
- Power Consumption – < 4mA per ADC channel
- Package – 48 pin, 6×6 mm2 QFN
The product page does not provide that much more information, but there’s apparently EVM which you can purchase by contacting the company.
I could not find pricing information, but X-Powers normally provides price-competitive solutions. I could not find any boards using AC108 yet, but we should get more info about that tomorrow.
Jean-Luc started CNX Software in 2010 as a part-time endeavor, before quitting his job as a software engineering manager, and starting to write daily news, and reviews full time later in 2011.
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The Achilles heel with mic arrays is that the neural networks used for hot word detection are proprietary and cost money to license. So far I have not been able to locate an open source solution that works very well.
One thing missing from the data, does this chip support on-chip hot word detection like the Conexant chips do? The Conexant chips are $7. On-chip hot word save a lot of power. The main system can stay in sleep mode while the mic chip continuously listens for the hot word. Without on-chip hot word detection this chip should cost under $1.
The DMIC pins appear to be support for MEMS digitial mics.
Seeed Studio has just launched a 4-mic array board based on AC108 -> https://www.cnx-software.com/2017/08/29/respeaker-4-mic-array-is-25-quad-microphone-add-on-board-for-raspberry-pi/