AKM Develops Ultra-Low Power Intelligent System Wakeup ADC With Integrated Acoustic Activity Analyzer

July 21 2020, 01:10
Asahi Kasei Microdevices Corporation (AKM) has developed the AK5706, a high-performance 24-bit stereo A/D converter (ADC) with an integrated Acoustic Activity Analyzer (AAA) wakeup solution consuming only 30μA, audio buffer, and support for digital and high-SNR microphones. Designed for systems that must listen for specific types of audio activity while consuming very low power, the AK5706 is ideal for products such as speech recognition systems, as well as security and smart home devices.

The AK5706 is a low-power, high-performance 24-bit stereo ADC with a dynamic range of 105dB (stereo 24-bit, 192kHz operation, 1.6mA consumption). The smarts of the AAA block make the AK5706 unique, but the ADC performance alone makes it ideal for wearables and other power-conscious mic-enabled products, as well as security devices that require high-quality far-field recording.

The AK5706’s AAA block continuously analyzes incoming audio against user-customized criteria while the rest of the system remains powered off. Within 7ms of detecting qualified audio, the AK5706 wakes the system and begins recording to its internal buffer, capturing any audio events that may occur while the SoC is booting. Once awake, the system SoC reads the buffer contents to determine what action to take.

The ability to qualify audio input while the rest of the system sleeps can drastically reduce a product’s standby power consumption and/or extend its battery life. The AK5706 is therefore ideal for applications such as smart speakers, wearable devices equipped with voice assistants, and connected security devices that listen for specific sounds. 

The AAA is more discerning than the typical level-triggered wakeup solution: it performs analog time- and frequency-domain analysis in order to determine whether audio content falls within the specified criteria. AKM's own ultra-low power analog technology (patent pending) enables the AAA to listen for relevant audio while consuming only 30μA.

The AAA’s Noise Level Detector acts as a gatekeeper: it constantly tracks the ambient noise level in order to reduce false positives that may otherwise occur in a noisy environment. If a sound is louder than the current noise floor by a user-specified delta, the AAA classifies the audio content as low- or high-frequency and short- or long-duration; the criteria for low vs high and short vs long are selected by the user. Human speech is generally low-frequency and long-duration, so a user looking for a wake-word may elect to reject any sounds that fall outside of those parameters. If the product designer wishes to wake the system on a door knock, they may look for low-frequency, short-duration sounds. Additionally, the AAA has a mode that exclusively detects T3 (smoke detector) and T4 (carbon monoxide detector) alarm sounds.
The AK5706’s external trigger input also allows to wake the system based upon stimuli from sensors such as human presence detectors, door sensors, and motion detectors. Even greater power savings may be achieved by using the external trigger input and AAA together, so that the AK5706 waits until human presence is detected (11μA) and only then starts listening for qualified audio (30μA).

The AK5706’s 64kB buffer can record up to two seconds of audio, depending upon quality and channel count, capturing audio that occurred during SoC boot. Data stored in the buffer can be read at high speed via SPI, making it suitable for smart speakers and other assistant-enabled devices that require real-time processing.

Samples are available now. Mass production of the AK5706 is scheduled for the fall of 2020.
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