Electret microphone
An electret microphone includes a microphone capsule with an output connection, a first input connection as an earth connection and a second input connection for providing a supply voltage and for leading out a microphone output signal. A cascode includes first and second transistors, wherein the microphone capsule's output is input to the cascode. The second transistor is an FET having a gate coupled to the microphone capsule's output connection and a drain coupled to the first transistor's emitter when bipolar or source when a FET. A third transistor, which is bipolar has an emitter coupled to the second input connection, a collector coupled via a capacitor to earth, and a base coupled via a resistance to the second input connection and the first transistor's collector when bipolar or drain when a FET, wherein a resistance exists between the second transistor's drain and the third transistor's collector.
1 . An electret microphone, comprising:
a microphone capsule with an output connection;
a first input connection as an earth connection and a second input connection for providing a supply voltage for the microphone capsule and for leading out a microphone output signal of the microphone capsule; and
a cascode consisting of a first and second transistor, wherein an output connection of the microphone capsule is provided as an input of the cascode,
wherein the second transistor is configured as a field effect transistor (FET) and a gate connection thereof is coupled to the output connection of the microphone capsule,
wherein a drain connection of the second transistor is coupled to an emitter connection of the first transistor as a bipolar transistor or to a source connection of the first transistor as a FET transistor,
a third transistor as a bipolar transistor, whose emitter connection is coupled to the second input connection,
wherein a collector connection of the third transistor is coupled via a third capacitor to the earth connection,
wherein a base connection of the third transistor is coupled via a first resistance to the second input connection,
wherein the base connection of the third transistor is coupled to a collector connection of the first transistor as a bipolar transistor or to a drain connection of the first transistor as a FET transistor,
wherein a fourth resistance is coupled between the drain connection of the second transistor and the collector connection of the third transistor.
2 . The electret microphone according to claim 1 , further comprising:
a third resistance between a source connection of the second transistor and the earth connection.
3 . The electret microphone according to claim 2 , wherein
the third resistance is configured as a temperature-dependent resistance.
4 . The electret microphone according to claim 1 , further comprising:
a series circuit comprising a sixth capacitor and a fifth resistance between the base connection of the third transistor and the second input connection of the electret microphone.
5 . The electret microphone according to claim 1 , further comprising:
a fourth capacitor between the source connection of the second transistor and the earth connection.
6 . The electret microphone according to claim 5 , wherein
a coil is provided between the earth connection and the fourth capacitor.
7 . The electret microphone according to claim 1 , further comprising:
a first capacitor between the output connection of the microphone capsule and the second input connection.
8 . The electret microphone according to claim 1 , wherein the first transistor is configured as a bipolar transistor, further comprising:
a twelfth resistance between the base connection of the first transistor and the second input connection; and
a series circuit comprising at least one diode and a resistance between the base connection of the first transistor and the source connection of the second transistor.
9 . The electret microphone according to claim 1 , wherein
a protective circuit comprising a first diode, a series circuit comprising an eleventh resistance and a first coil and a second capacitor is provided between the second input connection and the elements coupled thereto.
10 . An electret microphone, comprising:
a microphone capsule with an output connection,
a first input connection as an earth connection and a second input connection for providing a supply voltage for the microphone capsule and for leading out a microphone output signal of the microphone capsule; and
a cascode consisting of a first and a second transistor, wherein the output connection of the microphone capsule is provided as input of the cascode,
wherein the second transistor is configured as a field effect transistor (FET) and a gate connection thereof is connected to the output connection of the microphone capsule,
wherein a drain connection of the second transistor is coupled to an emitter connection of the first transistor as a bipolar transistor or to a source connection of the first transistor as a FET transistor,
a third transistor as a self-locking field effect transistor whose third connection is coupled to the second input connection,
wherein a second connection of the third transistor is coupled via a third capacitor to the earth connection,
wherein a gate connection is coupled as a first connection of the third transistor via a first resistance to the second input connection,
wherein the gate connection of the third transistor is coupled to a collector connection of the first transistor as a bipolar transistor or to a drain connection of the first transistor as a FET transistor,
wherein a fourth resistance is coupled between the drain connection of the second transistor and the second connection of the third transistor.