Sourcing guide:

MEMS sensor devices: Selection specifications, vendors and products-P3

MEMS Microphone:

Introduction: MEMS microphones are capacitive sensing devices. They feature a diaphragm as a capacitor plate that. Due the accoustic pressure of sound wave the diaphragm vibrate resulting in variation of the capacitance, that is then amplified by an associated semiconductor device to produce either an analog or digital output signal.

Key Specifications:

Sensitivity (dBFS): Sensitivity is a measure of the microphone output response to the acoustic pressure of a 1kHz 94dB Sound Pressure Level (1Pa RMS) sine wave. This is referenced to the output Full Scale Range (FSR) of the microphone.
FSR: Sensitivity, Electrical Noise Floor and Power Supply Rejection are measured with reference to the output FSR which is defined as the amplitude of 1kHz sine wave output whose positive peak value reaches 100% density of logic 1s and whose negative peak value reaches 0% density of the logic 1s.
Signal to Noise Ratio (dB): SNR is a measure of the difference in level between the output response of a 1kHz 94dB SPL sine wave and the idle noise output.
Directionality: Describes the pattern in which the microphone's sensitivity changes when the sound position in space.
Dynamic range: Is the measure of the difference between the loudest and the quietest SPLs to which the microphone responds linearly. The dynamic range of a microphone is not the same as its SNR.
MEMS microphones have two main characteristics that make them suitable for thin phone designs: small size and ability to withstand reflow temperature.
Frequency response: The high and low frequency limits are described as the points at which the microphone response is 3dB below the reference output level at 1kHz.
Power Supply Rejection Ratio(PSRR): Is a measurement of the microphone's ability to reject noise present on the power supply pins from the signal output.

Parts selection table from key MEMS microphone vendors

Data Sheet links:
http://www.analog.com/static/imported-files/data_sheets/ADMP504.pdf
http://www.knowles.com/search/prods_pdf/SPK0413LM4H-WB.pdf
http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/CD00284650.pdf
http://www.analog.com/static/imported-files/data_sheets/ADMP441.pdf
http://www.knowles.com/search/prods_pdf/SPA2410LR5H-B.PDF
http://www.knowles.com/search/prods_pdf/SPM0408HD5H-SB.PDF
http://www.knowles.com/search/prods_pdf/SPM0406HE3H-SB.PDF
http://www.akustica.com/Files/Admin/PDFs/DS25-1.0%20AKU230%20Datasheet.pdf
http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/DM00039779.pdf
http://www.wolfsonmicro.com/documents/uploads/data_sheets/en/WM7220.pdf
http://www.knowles.com/search/prods_pdf/SPM0407HE3H-SB.PDF
http://www.preciseley.com/product/mems_microphone.htm

New products highlights:
· Knowles ships 2 billionth SiSonic MEMS Microphone in May 2011; ranked as the world leader in MEMS-based Silicon microphone manufacturing. These SiSonic microphones are found in all Tier1 mobile phones as well as notebooks, headsets and digital still cameras. Knowles offers products of various ranges.
· Akustica's digital microphones are the world's first and only surface-mountable monolithic digital MEMS microphones that integrate an acoustic transducer, pre-amplifier, and sigma-delta modulator in a single chip of silicon that is only 0.7mm2.
· STMicro's MP34DB01 microphone is the only device in the market with real high-fidelity audio bandwidth, delivering flat frequency response in the full audio band of 20-20,000 Hz, coupled with an unparalleled signal-to-noise ratio (62 dB) and power-supply noise rejection (70 dB).
· STMicro's MP34DT01 microphone was designed to match the needs of AI speech-recognition systems - such as the recently introduced iPhone 4S's Siri - improving audio intelligibility without increasing the main-processor workload. The device's SNR also suits it for application in instruments such as phonometers that require high dynamic range.
· Higher sensitivity does not always indicate a better microphone. A microphone with higher sensitivity typically has less headroom between the output level under typical conditions, such as conversational speech, the maximum output level, etc.,

MEMS Oscillator: