Electret microphone

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Figure 1 - Typical electret condenser microphone capsules
Figure 1 - Typical electret condenser microphone capsules


A type of condenser microphone which eliminates the need for a power supply by using a permanently-charged material.



An electret is a stable dielectric material with a quasi-permanent electric charge that due to the high resistance of the material does not decay for hundreds of years. The term (coined this term in 1885 by Oliver Heaviside) is a combination of the two words electrostatic and magnet.

Figure 2 - Electret condenser microphone schematic
Figure 2 - Electret condenser microphone schematic

A typical electret microphone preamp circuit uses an FET in a common source configuration. The two-terminal electret capsule contains an FET which must be externally powered by supply voltage V+. The resistor sets the gain and output impedance. The audio signal appears at the output, after a DC-blocking capacitor.


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