Fully differential low-noise capacitor microphone circuit

A microphone circuit comprising:

• a capacitor capsule including a first terminal and as second terminal;
• first and second impedance converters connected differentially to the capacitor capsule, wherein the first impedance converter comprises a first field effect transistor including a gate connected to the first terminal of the capacitor capsule, wherein the second impedance converter comprises a second field effect transistor including a gate connected to the second terminal of the capacitor capsule, wherein the first impedance converter further comprises a first bootstrap capacitor and a first current source, and wherein the second impedance converter further comprises a second bootstrap capacitor and a second current source;
• first and second output buffer amplifiers connected differentially to the impedance converters, wherein the first and second output buffer amplifiers each form an emitter follower circuit, wherein the first output buffer amplifier comprises a first bipolar transistor including a base connected to a source of the first field effect transistor, and wherein the second output buffer amplifier comprises a second bipolar transistor including a base connected to a source of the second field effect transistor.

A method comprising the steps of:

• connecting first and second impedance converters to a capacitor capsule differentially by connecting the first impedance converter to a first terminal of the capacitor and connecting the second impedance converter to a second terminal of the capacitor.