Author:admin AddTime:2021-06-22
One side is separated from the metal pole plate with a thin insulating lining ring. In this way, a capacitor is formed between the vaporized gold film and the metal plate. When the electret diaphragm encounters sound wave vibration, it causes the electric field at both ends of the capacitor to change, thereby generating an alternating voltage that changes with the sound wave. The capacitance between the electret diaphragm and the metal plate is relatively small, generally tens of pF. Therefore, its output impedance value is very high (Xc = 1/2 ~ tfc), about tens of megaohms or more. Such a high impedance cannot be directly matched with an audio amplifier. Therefore, a junction field effect transistor is inserted into the microphone to perform impedance conversion. Field effect tubes are characterized by extremely high input impedance and low noise figure. Ordinary field effect transistors have three electrodes: the source (S), the gate (G) and the drain (D). What is used here is a special field effect tube with a diode compound between the internal source and the gate, as shown in Figure 2. The purpose of connecting the diode is to protect the FET when it is impacted by a strong signal. The grid of the field effect tube is connected to the metal plate. In this way, there are three output lines for electret microphones. That is, the source S, generally blue plastic wire, drain D, generally red plastic wire and braided shield wire connected to the metal shell.
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Shenzhen Shuyin Technology Co., Ltd. is a high-tech enterprise integrating microphone, microphone, Bluetooth headset, electronic audio-visual products and peripheral accessories of electronic digital products into one.
Email:lucy@soft-voice.com
Factory address: 2-4 / F, building a, No. 46-7, Hantang Second Road, Baoan community, Yuanshan street, Longgang District, Shenzhen