X-Powers AC108 is a Quad-Channel ADC Chip for Microphone Arrays

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 microphones arrays with support for 4 microphones, and a I2C + I2S output interface to the host processor. Microphone arrays are particularly useful for smartspeakers, 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-Power 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 devices.
    • I2S/PCM format using 2  pins to output 4 channel data of 1 devices.
    • TDM format using 1 pin to output 4 even 16 channel data of 4  devices.
    • Encoding format using 1 pins 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 provides that much more information, but there’s apparently EVM which you can purchase by contacting the company.

Click to Enlarge

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.

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Jon Smirl
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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.