The structure and principle of the capacitive microphone

Piezoelectric, Piezoresistive, and Capacitive are currently common micro microphone technologies. Piezoelectric microphones use the characteristics of piezoelectric materials to output current or voltage after being forced to convert sound signals into electrical signals and output them after being amplified, while piezoresistive microphones use piezoresistive materials to resist resistance after force. changes happened. Generally, the above two microphones are less sensitive to sound pressure and have higher system noise. Because of its excellent characteristics such as high sensitivity and low power consumption, condenser micro microphones are the mainstream of current market development.

The structure of a condenser microphone mainly uses two conductive plates and an insulating air layer between the two plates to form a basic capacitor structure. These two conductive plates are usually called "membrane" and "back plate" ( Backplate). The ideal diaphragm is a very soft elastic film, which will vibrate when subjected to sound pressure, resulting in a micro-distance change, resulting in dynamic micro-displacement between the diaphragm and the back plate, so that the capacitance value of the structure will also follow. change.

The structure principle of the condenser microphone: The sensor chip structure of the microphone is usually formed by a thin and low-stress polysilicon or silicon nitride diaphragm, and a thicker polysilicon or metal layer. The backplane with porous structure together forms a group of microcapacitor structures with air as the dielectric layer. In addition to the necessary sensors, another circuit chip is usually required in the microphone package to provide the stable bias voltage required for normal operation of the chip and output the signal after being amplified. It is generally referred to as ASIC. .

The purpose of the voltage doubler circuit is to boost the input power to provide the higher operating voltage required by the chip. The function of the amplifier circuit is to amplify and stabilize the input signal. The function of the voltage stabilizer is to provide voltage stabilization processing at the ASIC power input terminal, so that all circuit blocks inside the chip can operate normally. In addition to the three basic functional blocks mentioned above, the digital ASIC has also added a so-called "Sigma Delta Modulator" circuit to take charge of the tasks of signal sampling and noise suppression.