Detection and control of diaphragm collapse in condenser microphones
A condenser microphone is provided having a transducer element
. A diaphragm has an electrically conductive portion. A back-plate has an electrically conductive portion. A DC bias voltage element is operatively coupled to the diaphragm and the back-plate. A collapse detection element is adapted to determine a physical parameter value related to a separation between the diaphragm and the back-plate. A collapse control element is adapted to control the DC bias voltage element based on the determined physical parameter value.It is well-known that electrostatic actuators and sensors may enter an undesired so-called collapsed state under certain operating conditions such as, e.g., when exposed to extraordinarily high sound pressure levels or a mechanical shock.
The collapsed state is characterized by a "collapse" or sticktion between the diaphragm and the back-plate, such as that described in PCT patent application WO 02/098166 which discloses a silicon transducer element. When a polarity of anincoming sound pressure is such that the diaphragm, usually the moveable plate, is deflected towards the back-plate, the force originating from an impinging sound pressure is combined with an attractive force originating from a DC electrical fieldprovided between the diaphragm and the back-plate.
When a sum of these forces exceeds a predetermined critical value, an opposing force provided by a diaphragm suspension will be insufficient to prevent the diaphragm from approaching and contacting theback-plate, causing the microphone to enter a collapsed state. The diaphragm can only be released from the back-plate once the attractive force originating from the DC electrical field acting on the diaphragm has been removed or at least significantlyreduced in magnitude.
In silicon condenser microphones where no special means have been applied to prevent collapse of the diaphragm, fully or at least party removing the microphone DC bias voltage will remedy the collapsed state and secure that the transducer elementreturns to a normal or quiescent state of operation. Usually, the diaphragm and the back-plate condenser plates have both been treated with a non-conducting anti-sticktion coating which will prevent Van der Waal forces from keeping the diaphragmsticking even if the DC bias voltage that generates the DC electrical field between the transducer element diaphragm and back-plate has been removed (i.e., zeroed).
However, a collapse detection and control circuit adapted for use in condenser microphones has not yet been disclosed. The present invention is directed to satisfying this and other needs.
According to an embodiment of the invention, a condenser microphone is provided having a transducer element. A diaphragm has an electrically conductive portion. A back-plate has an electrically conductive portion. A DC bias voltage element isoperatively coupled to the diaphragm and the back-plate. A collapse detection element is adapted to determine a physical parameter value related to a separation between the diaphragm and the back-plate. A collapse control element is adapted to controlthe DC bias voltage element based on the determined physical parameter value.
According to an embodiment of the invention, an electronic circuit is provided for a condenser microphone having a transducer element. The circuit includes a DC bias voltage element to couple to a condenser microphone diaphragm and a back-plate. A collapse detection element is adapted to determine a physical parameter value related to a separation between the diaphragm and the back-plate of the condenser microphone. A collapse control element is adapted to control the DC bias voltage elementbased on the determined physical parameter value.
According to an embodiment of the invention, a method of operating a condenser microphone is provided. An acoustic signal is transduced into an electrical signal with a transducing element. The transducing element has a diaphragm and aback-plate. A physical parameter value is determined that relates to a separation between the diaphragm and the back-plate. An appropriate separation between the diaphragm and the back-plate is maintained by controlling a DC bias voltage between thediaphragm and the back-plate.
Detection and control of diaphragm collapse in condenser microphones
By: Rebecca