These tight performance characteristics are particularly beneficial when MEMS microphones are used in array applications. Furthermore, semiconductor fabrication technology and the inclusion of audio preamplifiers enables manufacturing MEMS microphones with closely matched and temperature stable performance characteristics. In high vibration environments, the use of MEMS microphone technology can reduce the level of unwanted noise introduced by the mechanical vibration. The relatively low output impedance of analog MEMS microphones and the outputs from digital MEMS microphones are ideal for applications in electrically noisy environments. For instance, space constrained applications will find the small package sizes available for MEMS microphones attractive, while a reduction in both PCB area and component cost can be realized thanks to the analog and digital circuits included in the MEMS microphone construction.
The market share for MEMS microphones continues to grow at a rapid pace due to many advantages provided by this newer technology.
There are many considerations when selecting between an ECM and MEMS microphone. ECM application schematic Differences in Microphone Technologies The JFET is typically configured in a common-source configuration, while an external load resistor and dc blocking capacitor are used in the external application circuit. The capacitor voltage variations are amplified and buffered by a JFET internal to the microphone housing. Voltage across the capacitor varies as the value of the capacitance changes due to sound pressure waves moving the electret diaphragm, ΔV = Q/ ΔC. Typical electret condenser microphone constructionĪn electret diaphragm (material with a fixed surface charge) is spaced close to a conductive plate, and similar to MEMS microphones, a capacitor is formed with the air gap as the dielectric. Left: analog MEMS microphone application schematic Right: digital MEMS microphone application schematic Electret Condenser Microphone BasicsĮlectret Condenser Microphones (ECM) are constructed as shown in the figure below. This means the microphone can connect directly to a digital signal processor (DSP) or microcontroller, eliminating the need for an ADC or codec in many applications. Digital I²S outputs are a third option that include an internal decimation filter, which allows for processing to be completed in the microphone itself. Decoding of the digital signal at the receiver is simplified due to the single bit encoding of the data. A common format used for the digital encoding in MEMS microphones is pulse density modulation (PDM), which allows for communication with only a clock and a single data line. If a digital output signal is desired, then an analog-to-digital converter (ADC) is included on the same die as the audio preamplifier. The output of the audio preamplifier is provided to the user if an analog output signal is desired. MEMS microphones typically contain a second semiconductor die which functions as an audio preamplifier, converting the changing capacitance of the MEMS to an electrical signal. The MEMS diaphragm forms a capacitor and sound pressure waves cause movement of the diaphragm. The MEMS component is often designed with a mechanical diaphragm and mounting structure created on a semiconductor die. A small hole is fabricated in the case to allow sound into the microphone and is either designated as top-ported if the hole is in the top cover or bottom-ported if the hole is in the PCB.
MEMS microphones are constructed with a MEMS (Micro-Electro-Mechanical System) component placed on a printed circuit board (PCB) and protected with a mechanical cover. With that in mind, we will review MEMS and electret condenser microphone basics, compare the differences between the technologies, and outline the advantages of each solution. Although the two technologies work on similar principles, there are many use cases for choosing one over the other. The correct microphone makes it possible for applications to accurately capture almost any sound, with the two most common technologies used for constructing microphones being MEMS and electret condenser. Perhaps you remember the marketing campaign from a few years ago with the phrase, "Can you hear me now?" More and more devices being designed today, from wearables to home assistants, are being asked to "hear" their environment.