AKM developed the AK5704EN low-power 4-channel 32-bit A/D converter (ADC) with integrated low-noise microphone amplifiers and digital signal processing blocks, such as filtering and level control, that are required for a digital microphone input with superior low-noise recording capabilities and low power consumption. Integrated features include programmable phase adjustment, microphone sensitivity adjustments, programmable digital filters with 2nd order HPF and LPF, automatic level control, PLL and even a digital Voice Activity Detector.
Featuring a dynamic range reaching 105dB and with -90dB THD+N, the new AK5704EN 4-channel 32-bit A/D converter supports sampling frequencies from 8 to 192kHz and its built-in microphone amplifier and power supply make it an ideal solution for conference systems, microphone array systems or smart speakers, enabling these products to take advantage of the full performance of high-SNR microphones.
According to AKM, the solution is ideal for high-resolution recordings, as well as applications requiring excellent far-field response over 5 meters. The AK5704 is also extremely power-efficient, consuming only 17mW in active mode. The AK5704EN incorporates a new Voice Activity Detector (VAD), which enables a boot trigger that can significantly reduce system power consumption, as the rest of the device may be powered off while the VAD consumes only 2.7mW while waiting for a wake-word.
For microphone arrays, multiple AKM AK5704EN devices may be connected in parallel to create a system supporting up to 16 microphones. Since the converter supports sampling frequencies up to 192kHz, it can be also combined with a wideband microphone to achieve ultrasonic band recording. It offers two types of digital filters - Short Delay Sharp Roll-off and Voice - which can be used to easily tune different applications from its single-ended microphone amplifiers or full-differential inputs, providing gains from 0 to +30dB in 3dB steps.
In terms of connectivity, the AKM AK5704EN uses the standard I2S digital audio interface and I2C for control I/F (400kHz). There are two microphone power supply outputs with 2.8V, 2.5V, 1.8V, and AVDD with system power supply options from 1.7 to 1.9V or 3.0 to 3.6V. Power consumption is reduced to 9.7mW in 2-channel model, all the way to 17.0mW in 4-channel ADC mode, with the option to go as low as 2.7mW using a 16kHz slave mode. Mass production of the AK5704 is scheduled for September 2019, available in 28-pin QFN (4mm x 4mm, 0.4mm pitch) packages.
High Resolution DSPs for Audio and Voice
The second announcement from AKM were the AK7739VQ and AK7737VQ multicore audio processors, the first offering 4-channel A/D and D/A plus 12-channel sample rate conversion, while the AK7737VQ is a 4-channel ADC only with 12ch SRC. According to the Japanese company, these two new updated audio processors were designed for the latest challenges in scenarios such as listening to wireless sound at home or while driving and talking on a hands-free call in automotive environments.
These two new multifunction audio processors are improvements to the existing AK7738, which has been adopted in various in-vehicle head units for processing high resolution sound sources. The expansion introduces updated specifications to 32-bit audio DSP, supporting floating point arithmetic, and uses AKM's “Velvet Sound” technology on the analog outputs, enabling high-quality playback of high-resolution sound sources.
The new AK7739/AK7737 chips essentially inherit the functions from the well-established AK7738 while upgrading the three DSP cores, Audio I/O, ADC and SRC. The AK7739/AK7737 support 32-bit floating point arithmetic - improved from the 28-bit floating point of the AK7738 - and now greatly expands the chips parallel operation capability of 6144 steps/fs x2, (at 48kHz sampling). In addition, the RAM is freely programmable for user applications, making it possible for various audio processing functions such as surround sound, parametric equalization, and various sound effects. The integrated large memory eliminates the need for external program memory. Programs are loaded into the RAM via a serial interface from a microcontroller, allowing for seamless updates.
Differences between the two new chips are essentially the use of Velvet Sound technology in the AK7739 model, which is also and advanced two-channel 32-bit DAC and 2-channel 24-bit A/D converter with microphone amplifier and input selector, while the AK7737 is ADC only. The AK7739 has two stereo ADC’s, two stereo DAC’s, and four asynchronous stereo SRC’s and four mono SRC’s, making it possible to compose the main block of an audio system without requiring additional audio components. The internal path connection of the AK7739/AK7737 can be set freely via register settings.
Audio I/O for both chips includes 6 digital input/output ports (TDM I/F, Max 96ch). An integrated microphone amplifier and microphone bias circuit reduce the mounting area of the printed board. Both the AK7739/AK7737 can provide signals to a class-D amplifier and receive input data from external digital audio sources. The automotive grade AK7739VQ and the AK7737VQ ADC are both now available to the market in 64-pin HTQFP packages.