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MT8516 Enables Google Assistant

July 11, 2017

Author: Mike Demler

The MediaTek MT8516 is purpose built to serve the growing market for voice-enabled digital assistants. It integrates four Cortex-A35 CPUs clocking at up to 1.3GHz, along with 2.4GHz Bluetooth 4.0 and 802.11b/g/n Wi-Fi transceivers. The first products using the new chip are likely to ship in 4Q17.

Each CPU core in the MT8516 has a 32KB L1 cache, and the four cores share a 512KB L2 cache. The chip’s DRAM interface works with LPDDR2/3, DDR3/3L, and DDR4. To handle the multi-microphone setups typical of Amazon Echo, Google Home, and other smart speakers, the MT8516 supplies inputs for eight time-division-multiplexed (TDM) microphone channels. It additionally includes two pulse-density-modulated (PDM) microphone channels, which commonly serve in smartphones and tablets but are also useful for portable voice-enabled speakers such as the Echo Tap. MediaTek probably repurposed an audio codec from one of its mobile processors to handle the microphone signals. Audio output is through the integrated DAC or the four-channel I2S interface.

In lieu of using a DSP core to handle on-chip voice processing, the MT8516 runs the Google Assistant SDK’s audio algorithms on its Cortex-A35 CPUs with Neon SIMD extensions. An audio-optimized DSP would enable more sophisticated noise cancellation and filtering to improve accuracy, and consume less power, but MediaTek based this design on its previous success in Amazon’s second-edition Echo Dot. That compact Alexa-enabled device repurposes the MT8163 tablet processor, which also lacks a DSP. The company designed the MT8516 for always-on voice-detection in AC-powered devices, so it didn’t integrate a power-saving MCU that would enable the chip to sleep until it detects a command phrase.

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