Comparing MEMS and Electret
Condenser (ECM) Microphones
A free comparing guide for Same Sky MEMS and electret condenser (ECM) microphones.
MEMS MICROPHONE BASICS
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. 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. The MEMS component is often
designed with a mechanical diaphragm and mounting structure created on a semiconductor die
The MEMS diaphragm forms a capacitor and sound pressure waves cause movement of the
diaphragm. 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
output of the audio preamplifier is provided to the user if an analog output signal is desired. If a
digital output signal is desired, then an analog-to-digital converter (ADC) is included on the same
die as the audio preamplifier. 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. Decoding of the digital signal at the receiver is simplified due to the single bit encoding of
the data. Digital I²S outputs are a third option that include an internal decimation filter, which allows
for processing to be completed in the microphone itself. 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.
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. 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. Although the two
technologies work on similar principles, there are many use cases for
choosing one over the other. 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.
Figure 1
Typical MEMS
microphone
construction
3
Comparing MEMS and Electret
Condenser (ECM) Microphones
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ELECTRET CONDENSER MICROPHONE BASICS
Electret Condenser Microphones (ECM) are constructed as shown in the figure below.
An 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.
Voltage across the capacitor varies as the value of the capacitance changes due to sound pressure
waves moving the electret diaphragm, ΔV = Q/ ΔC. The capacitor voltage variations are amplified
and buffered by a JFET internal to the microphone housing. The JFET is typically configured in a
common-source configuration, while an external load resistor and dc blocking capacitor are used in