Microphone amplifying circuit design method and microphone amplifying circuit

A microphone amplifying circuit design method, applied to a microphone and an amplifying circuit, the amplifying circuit including an amplifier, a bias resistor connecting to an input of the amplifier by which the amplifier is connected to a bias voltage, an input end connecting to the input of the amplifier and an output end connecting to the amplifier;

• the method including steps of:
• providing a layer of underlying metal set between a substrate of an integrated circuit and a welding plate;
• wherein the welding plate, the underlying metal and the substrate are insulated from each other, a first parasitic capacitor is formed between the welding plate and
• the underlying metal, and a second parasitic capacitor is formed between the underlying metal and the substrate;
• seeking a circuit point circuit point in the amplifying circuit, and making the circuit point satisfy the following conditions which are that:
• a. the circuit point and the input end are in a same phase;
• b. a voltage gain of the circuit point and the input end is greater than or equal to 0.8;
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• c. the circuit point is in a signal path from the input end to the output end;
• connecting the underlying metal to the circuit point, and connecting the welding plate to the input end;
• welding the microphone to the welding plate of the integrated circuit to connect the microphone and act as a microphone capacitor;
• wherein one end of the microphone capacitor is connected to a high voltage bias voltage, and an other end of the microphone capacitor is connected to the input end;
• one end of the first parasitic capacitor is connected to the input end, and an other end of the first parasitic capacitor is connected to the output end;
• the second parasitic capacitor is connected to the output end, and an other end of the second parasitic capacitor is grounded.