MEMS microphone technology adapting to changing use cases: Page 4 of 5

April 13, 2017 //By Masahito Kanaya
Owners of devices such as smartphones and tablets continually want to be able to use their gadgets in new ways, and at the same time expect extremely high performance. On-board audio functionality is a prime example. People want to be able to record social events, music performance and expect accurate, lifelike playback, or to enjoy high voice-call quality free of background noise even when outside or travelling in a car. There is also demand for high audio quality when capturing sounds further from the microphone.

ON Semiconductor has focused on developing highly integrated ASICs for digital MEMS microphones, ready to be combined with any of a variety of MEMS transducers made by independent MEMS suppliers. An example is the LC706200 digital IC family, which integrates a feed-forward delta-sigma ADC in addition to an analog amplifier and low-pass filter, as shown in figure 4. There is also a charge pump that provides the operating voltage for the MEMS transducer.

Figure 4: A feed-forward delta-sigma ADC enables a small-footprint microphone with digital output.

ON Semiconductor’s digital ASICs can help overcome the challenges facing today’s MEMS microphone designers by satisfying key performance criteria. Among these, a high SNR is required to allow clear performance when microphones are used at greater distances, as well as for cleaner audio capture generally.

In particular, automatic speech recognition algorithms depend on high SNR to achieve good word accuracy rates. ASICs with SNR greater than 64 dB are expected today, complementing advances achieved by MEMS engineers to optimise the characteristics of the transducer.

As end users seek better results from devices like smartphones in an increasing variety of use cases, there is demand for microphones that can operate without distortion up to high Sound Pressure Levels (SPL) as encountered in loud environments. One example is to allow high-quality recording for social users to capture their experiences at music festivals. 

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