Digital MEMS microphones are rapidly gaining popularity in mobile platforms, thanks to their small size and superior digital signal processing capabilities. A typical digital MEMS microphone array uses the same power supply as the speech processing chip. The array is configured with one main microphone and one reference microphone, which captures proximal audio signals. These signals are amplified and converted to Pulse Density Modulation (PDM) signals, which are then sent to the speech processing chip.
Digital MEMS Microphone Array in Mobile Phones
On mobile platforms, such as those powered by MediaTek (MTK), a typical handheld mode application involves the microphone array capturing proximal signal differences to perform steady-state and non-steady-state noise suppression, as well as linear echo cancellation. Once processed, the signal is converted to a 16-bit PCM signal and sent to the baseband chip as the uplink signal. Simultaneously, it produces sidetone audio that is sent to the receiver. The downlink signal is transmitted to the input pin of the baseband chip, where it undergoes noise suppression. Based on the noise information provided by the microphone array, the clear voice engine may be activated to enhance the volume of the receiver, ensuring that users can hear clearly even in noisy environments.
Hands-Free Mode
In hands-free mode, the microphone array captures the echo signals, which are then used to cancel the acoustic echo from the captured proximal voice. The processed signal undergoes steady-state noise suppression before being transmitted as an uplink signal to the baseband chip. The downlink signal passes through the baseband chip to the input pin, where noise suppression is applied. Again, the microphone array's noise information is used to determine if the clear voice engine should be activated to improve the receiver's volume, allowing users to hear clearly even in noisy environments, while also serving as a reference for echo cancellation.
In both handheld and hands-free modes, digital MEMS microphone arrays ensure high-quality voice communication by effectively reducing noise and echo, enabling clear and intelligible speech even in challenging environments.
