Detection and control of diaphragm collapse in condenser microphones

1. A condenser microphone comprising:

a transducer element comprising:

a diaphragm having an electrically conductive portion;

a back-plate having an electrically conductive portion;

a DC bias voltage element operatively coupled to the diaphragm and the back-plate;

a collapse detection element adapted to determine a physical parameter value related to a separation between the diaphragm and the back-plate; and

a collapse control element adapted to control the DC bias voltage element based on the determined physical parameter value.

2. The condenser microphone according to claim 1 , wherein the collapse detection element is adapted to determine at least one of an instantaneous value of the physical parameter, and a short-term average value of the physical parameter.

3. The condenser microphone according to claim 1 , wherein the collapse control element is adapted to avoid collapse of the transducer element.

4. The condenser microphone according to claim 1 , wherein the collapse control element is adapted to allow collapse of the transducer element, and adapted to remedy a collapsed condition with a discharge element operatively coupled to the transducer element and adapted to discharge the transducer element for a predetermined discharge time.

5. The condenser microphone according to claim 4 , wherein the predetermined discharge time has a duration between 1 ms and 1 second.

6. The condenser microphone according to claim 4 , wherein the discharge element includes a controllable MOS transistor.

7. The condenser microphone according to claim 1 , wherein the collapse detection element is adapted to determine a capacitance of the transducer element.

8. The condenser microphone according to claim 1 , wherein the collapse detection element is adapted to determine the physical parameter value by applying a probe signal to the transducer element.

9. The condenser microphone according to claim 8 , wherein the probe signal includes a signal selected from the group consisting of: DC signals and ultrasonic signals.

10. The condenser microphone according to claim 1 , wherein the collapse detection element includes a capacitive divider having a cascade between a fixed capacitor and a capacitance of the transducer element.

11. The condenser microphone according to claim 1 , wherein the collapse detection element is responsive to a sound pressure impinging on the diaphragm.

12. The condenser microphone according to claim 11 , wherein the collapse detection element includes a sensor microphone positioned in proximity to the transducer element and operatively coupled to the collapse control element.

13. The condenser microphone according to claim 1 , wherein the collapse detection element is adapted to detect a peak voltage generated by the transducer element.

14. The condenser microphone according to claim 1 , wherein the collapse control element is adapted to reduce a DC bias voltage across the transducer element based on the determined physical parameter value.

15. The condenser microphone according to claim 14 , wherein the collapse control element includes a bias current monitoring element adapted to detect a DC current flow from the DC bias voltage element to the transducer element.

16. The condenser microphone according to claim 14 , wherein the collapse control element is adapted to electrically connect the diaphragm and the back-plate upon the determined physical parameter value exceeding a predetermined threshold.

17. The condenser microphone according to claim 14 , wherein the collapse control element comprises

a controllable element adapted to generate an electrical pulse with a predetermined duration and amplitude based on the determined physical parameter value, and

a switch element adapted to receive the electrical pulse and to electrically connect the diaphragm and the back-plate in response to a receipt of the electrical pulse.

18. The condenser microphone according to claim 14 , wherein the collapse control element is adapted to reduce the DC bias voltage based on the determined physical parameter value.

19. The condenser microphone according to claim 1 , wherein the transducer element includes a silicon transducer.

20. The condenser microphone according to claim 19 , wherein the silicon transducer is implemented on a first silicon substrate, and wherein the collapse detection element and the collapse control element are implemented on a second silicon substrate.

21. The condenser microphone according to claim 19 , wherein the silicon transducer, the collapse detection element and the collapse control element are monolithically integrated on a single die.

22. The condenser microphone according to claim 21 , wherein the die further includes a preamplifier operatively coupled to the transducer element.

23. An electronic circuit for a condenser microphone having a transducer element, the circuit comprising:

a DC bias voltage element to couple to a condenser microphone diaphragm and a back-plate;

a collapse detection element adapted to determine a physical parameter value related to a separation between the diaphragm and the back-plate of the condenser microphone; and

a collapse control element adapted to control the DC bias voltage element based on the determined physical parameter value.

24. The electronic circuit according to claim 23 , wherein the collapse detection element is adapted to determine a capacitance of the transducer element.

25. The electronic circuit according to claim 23 , wherein the collapse detection element is adapted to determine the physical parameter value by applying a probe signal to the transducer element.

26. The electronic circuit according to claim 23 , wherein the collapse detection element is adapted to detect a peak voltage of the transducer element.

27. The electronic circuit according to claim 23 , wherein the collapse control element is adapted to adaptively reduce a DC bias voltage based on the determined physical parameter value.

28. The electronic circuit according to claim 23 , wherein the collapse control element includes a discharge element operatively coupled to the transducer element and adapted to discharge the transducer element for a predetermined discharge time.

29. A method of operating a condenser microphone comprising:

transducing an acoustic signal into an electrical signal with a transducing element having a diaphragm and a back-plate;

determining a physical parameter value that relates to a separation between the diaphragm and the back-plate; and

maintaining an appropriate separation between the diaphragm and the back-plate by controlling a DC bias voltage between the diaphragm and the back-plate.

controlling a DC voltage between in response to the physical parameter value to maintain.

30. The method according to claim 29 , further including remedying a collapsed condition with a discharge element operatively coupled to the transducer element and adapted to discharge the transducer element for a predetermined discharge time.