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How Excellent MEMS Microphones Turn Laptops into Communication Systems

Figure 5: All building blocks contribute to the self-noise of a microphone.

of –26 dBFS. Two sets of data were of the laptop as a conference device over long develops and produces all three building
compared: audio picked up by the built-in distances, whereas the current built-in micro- blocks itself; thus, the company can easily
microphones and audio picked up by h phones do not pick up voice in good quality identify this combination.
igh-SNR microphones. Both datasets were under those conditions. For distances of about Infineon continuously applies its expe-
processed by a standard voice-over-IP 5 meters, this translates to a quality improve- rience and know-how to bring even better
program used for calls. ment of over 30%. It makes the laptop suited microphones to the market. The latest port-
for bigger meeting rooms and gives the user a folio additions are the XENSIV™ IM73A135
HIGH-SNR MICROPHONE LEADS TO greater range of movement. and the IM69D127, which use Infineon’s
BETTER VOICE COMMUNICATION It’s clear that the quality of the microphone patented Sealed Dual Membrane (SDM) tech-
Figure 4 shows the MOS results comparing is crucial for excellent speech transmission. nology. Both feature excellent AOP
the laptop and the high-SNR microphone, But how can better MEMS microphones be (135 and 127 dB SPL, respectively) and
i.e., IM69D120. It can be clearly seen that the achieved? To get to the bottom of this, let’s first SNR (73 and 69 dB, respectively). Both
high-SNR microphone provides significantly look at the components of a MEMS microphone. microphones are well-suited for com-
higher performance for voice communication munication devices and earphones with
than the built-in microphone. For normal or BUILDING BLOCKS OF A MEMS audio-critical functionalities such as ANC
quiet speech, a microphone with higher SNR MICROPHONE and transparent hearing. With its small
improves the perceived speech quality from A MEMS microphone essentially consists footprint of 3.6 mm × 2.5 mm × 1 mm, the
fair to good or from good to excellent. of three building blocks: First, the actual IM69D127 is especially suited for size-
The tests were performed for three scenar- sensing element, the name-giving microelec- constrained applications like earbuds.
ios, in all of which the high-SNR microphone tromechanical system. Sound waves move a
showed superior performance. In the close membrane, which forms a capacitor with the CONCLUSION
scenario, the speaker is less than 1 meter away backplate. The resulting changes in capac- The latest MEMS technology brings
from his/her device. The better microphone itance generate the electrical signal. The studio-level audio performance to
results in better call quality, reduces the need second building block, the ASIC, contains the consumer devices. Infineon has been able
for a headset, and gets rid of the “you sound so charge pump for the membrane, the amplifier to demonstrate in experiments that the
far away” effect. stages, an LDO for clean power supply, audio quality of a device, such as a laptop,
For distances between 1 and 3 meters, and the calibration logic. These parts are can be significantly improved by using
high-SNR microphones “free” the user from integrated together into the third building better microphones. The company’s new
the desk. They showed an overall speech block, the package. The package protects the XENSIV™ IM73A135 and IM69D127 MEMS
quality improvement of over 15%. The component, shields it (EMI), and forms an microphones enable customers to take their
speaker can stand up and move around while acoustical back volume. devices to the next level of audio quality.
on a call. It allows for a more flexible posi- Because all three building blocks of the In the coming quarters, Infineon is work-
tioning of the laptop on the desk, e.g., beside MEMS have a strong influence on perfor- ing on new digital and analog microphones
an external screen. mance (Figure 5), the optimal combination that will push the limits of small size and
High-SNR microphones even enable the use must be found for each application. Infineon high SNR even further. ■

www.eetimes.eu | JUNE 2021