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How Excellent MEMS Microphones Turn Laptops into Communication Systems

Figure 2: Setup of the POLQA test. An artificial mouth (A) is placed at the same height as the laptop mic (B) that is positioned on the top
part of the front bezel above the screen and next to the camera module. The laptop is placed at a fixed distance of 1 meter (C) from the
artificial mouth. Distances above 1 meter are simulated based on inverse square law. The laptop has a VoIP connection (D) to another
laptop (E) outside the anechoic chamber. The outer laptop (E) also works as a transmitter to the artificial mouth over a wired channel (F).
The block diagram in Figure 3 explains the signal flow in much more detail.

small and mass-produced with very tight a standard reference signal. All elements of and recordings even at longer distances. A
manufacturing tolerances — this is offered by the microphone (MEMS, ASIC, package, and larger SNR is thus required.
MEMS technology. Until now, designers had to sound ports) contribute to the self-noise. The total harmonic distortion refers to
find a tradeoff between size and performance. The SNR is relevant, for example, when the harmonics of an input signal that are not
it comes to detecting sounds/voices from a present in the input signal itself. The acous-
CHARACTERISTICS OF MICROPHONES greater distance. The sound level is halved at tic overload point (AOP) is defined as the
But how do you describe the performance twice the distance, so the input signal also point where the distortions reach 10%: The
characteristics of a microphone qualitatively? decreases. Sound channel, room conditions, signal is too loud for the microphone and
First, there is the signal-to-noise ratio (SNR), and system design cause further signal artifacts/clipping noises are present in the
which describes the difference between the losses. A good microphone is required to cap- output. The AOP thus denotes the maximum
inherent self-noise of the microphone and ture input for voice commands, algorithms, volume that the microphone can handle.

Figure 3: Block diagram detailing the POLQA test

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