Microphone assembly with P-type preamplifier input stage

1. A microphone assembly comprising:

a condenser transducer element having a displaceable diaphragm and a back-plate, the displaceable diaphragm and the back-plate being arranged to form a capacitor in combination;

a preamplifier circuit having an input stage comprising a P-type field effect transistor; and

a microphone bias voltage source adapted to provide a DC bias voltage between the back-plate and the displaceable diaphragm, the microphone bias voltage source being integrated on an electronic or integrated semiconductor circuit die together with the input stage P-type field effect transistor;

wherein the displaceable diaphragm and the back-plate are operatively connected between a source input and a gate input of the P-type field effect transistor, the back-plate being operatively connected to the gate input, and the displaceable diaphragm being operatively connected to the source input; and

the displaceable diaphragm and the source input are configured to be referenced to an external power supply voltage.

2. A microphone assembly according to claim 1 , wherein each of the back-plate and the gate input of the P-type field effect transistor is operatively connected via a DC voltage blocking element.

3. A microphone assembly according to claim 2 , wherein the DC voltage blocking element comprises a capacitor.

4. A microphone assembly according to claim 1 , wherein the microphone bias voltage source is operatively connected to the back-plate via a high impedance element having a resistance larger than 10 Giga Ohms.

5. A microphone assembly according to claim 4 , wherein the high impedance element is selected from the group consisting of a resistor and a reverse biased semiconductor diode.

6. A microphone assembly according to claim 1 , wherein the condenser transducer element comprises a MEMS-based transducer.

7. A microphone assembly according to claim 1 , wherein the P-type field effect transistor is selected from the transistor group consisting of: JFET and MOS transistors.

8. A microphone assembly according to claim 1 , wherein the condenser transducer element further comprises a bulk part operatively connected to the displaceable diaphragm.

9. A microphone assembly according to claim 1 , wherein the condenser transducer element further comprises a bulk part operatively connected to ground.

10. A microphone assembly according to claim 1 , wherein the back-plate or the displaceable diaphragm is provided with a permanent electrically pre-charged layer.

11. A portable communication device comprising the microphone assembly according to claim 1 .

12. A portable communication device according to claim 11 , wherein the portable communication device is selected from the group consisting of a cell phone, a hearing aid, a PDA, and any combination thereof.

13. A method of processing an electrical signal from a condenser transducer element having a displaceable diaphragm and a back-plate, the method comprising the steps of:

providing the condenser transducer element with the displaceable diaphragm operatively connected to a source input of a P-type field effect transistor;

providing a DC bias voltage to the back-plate by a microphone bias voltage source being integrated on an electronic or integrated semiconductor circuit die together with the input stage P-type field effect transistor;

providing an external supply voltage to the displaceable diaphragm and the source input;

providing the condenser transducer element with the back-plate operatively connected to a gate input of the P-type field effect transistor; and

processing an electrical signal provided at the drain output of the P-type field effect transistor.

14. A method according to claim 13 , wherein each of the back-plate and the gate input of the P-type field effect transistor is operatively connected via a DC voltage blocking element.

15. A method according to claim 14 , wherein the DC voltage blocking element comprises a capacitor.

16. An integrated semiconductor circuit comprising:

a preamplifier circuit having an input stage comprising a P-type field effect transistor, the preamplifier circuit comprising a first externally accessible input terminal operatively connected to a source input of the P-type field effect transistor and a second externally accessible input terminal operatively connected to a gate input of the P-type field effect transistor; and

a microphone bias voltage source adapted to provide a DC bias voltage to the second externally accessible input terminal so as to provide a DC bias voltage for one of the displaceable diaphragm and the back-plate, the microphone bias voltage source being integrated on an electronic or integrated semiconductor circuit die together with the input stage P-type field effect transistor,

wherein the first and second input terminals are operatively connectable to an associated displaceable diaphragm and an associated back-plate, respectively, of a condenser transducer element, the back-plate being operatively connected to the gate input of the P-type field effect transistor, and the displaceable diaphragm being operatively connected to the source input of the P-type field effect transistor; and

the displaceable diaphragm and the source input are configured to be referenced to an external power supply voltage.

17. An integrated semiconductor circuit according to claim 16 , further comprising a DC blocking element inserted between the second externally accessible input terminal and the gate input of the P-type field effect transistor.

18. An integrated semiconductor circuit according to claim 16 , further comprising voltage a regulator providing a regulated DC voltage, the voltage regulator being operatively coupled to the source input of the P-type field effect transistor.

19. An integrated semiconductor circuit according to claim 18 , wherein the regulated DC voltage is set to a value between 0.9 volts and 5.0 volts.

20. An integrated semiconductor circuit according to claim 19 , wherein a DC voltage difference between the DC bias voltage and the regulated DC voltage is set to a value between 4.0 volts and 20.0 volts.