Amplitude-modulated electro-mechanical feedback system for silicon condenser microphones

For silicon condenser microphones, narrowing the air gap as a part of the miniaturization process causes a reduction of the bandwidth of the microphone. By introducing an actuator electrode on the diaphragm for electro-mechanical feedback, it is possible to increase the bandwidth of condenser microphones with a narrow air gap. A feedback system is presented, which uses an amplitude-modulated actuator signal with a carrier frequency far above the audio-frequency range. With feedback, the bandwidth of the microphone is increased by at least a factor 10.