System and method for sensing capacitance change of a capacitive sensor

1. A capacitive sensing circuit comprising:

a capacitive sensor having a sensor output;

a programming circuit having a programming circuit output coupled to the sensor output of the capacitive sensor, the programming circuit having a programming transistor having a source, a floating gate, and a drain, the floating gate being the programming circuit output;

an amplifier having a first amplifier input and an amplifier output, the first amplifier input being coupled to the programming circuit output of the programming circuit; and

a first capacitor having a first terminal and a second terminal, the first terminal coupled to the floating gate of the programming transistor, and the second terminal coupled to a ground.

2. The circuit according to claim 1 , wherein the amplifier is a first order amplifier.

3. The circuit according to claim 1 , wherein the capacitive sensor is a MEMS sensor.

4. The circuit according to claim 1 , wherein the capacitive sensor is a CMUT.

5. The circuit according to claim 1 , the programming circuit further having a programming circuit input, wherein the programming circuit input of the programming circuit is coupled to the amplifier output of the amplifier.

6. The circuit according to claim 1 , wherein the sensor output of the capacitive sensor is coupled to the first amplifier input of the amplifier through a capacitor network.

7. The circuit according to claim 1 , wherein the programming circuit is adapted to control a charge on the first amplifier input of the amplifier.

8. A capacitive sensing circuit comprising:

a capacitive sensor having a sensor output;

a programming circuit having a programming circuit output coupled to the sensor output of the capacitive sensor;

an amplifier having a first amplifier input and an amplifier output, the first amplifier input being coupled to the programming circuit output of the programming circuit;

a buffer circuit having a buffer input coupled to the amplifier output of the amplifier, and a buffer output; and

a comparator having an inverting input and a non-inverting input, the non-inverting input coupled to the buffer output of the buffer;

wherein the inverting input of the comparator is adapted to receive a comparator voltage, and

wherein a comparator output of the comparator is connected to a drain of a programming transistor in the programming circuit.

9. The circuit according to claim 8 , wherein the programming circuit comprises:

a programming transistor having a source, a floating gate and a drain; and

wherein the floating gate is the programming circuit output.

10. The circuit according to claim 9 , further comprising a tunneling capacitor having a first terminal and a second terminal, the first terminal coupled to the first amplifier input of the amplifier, and the second terminal adapted to receive a tunneling voltage.

11. The circuit according to claim 9 , further comprising a first capacitor having a first terminal and a second terminal, the first terminal coupled to the floating gate of the programming transistor, and the second terminal coupled to a ground.

12. The circuit according to claim 8 , wherein the programming circuit comprises a pseudo resistor having a first terminal and a second terminal.

13. The circuit according to claim 12 , wherein the pseudo resistor comprises:

a first transistor having a first source, a first drain, a first gate, and a first well;

a second transistor having a second source, a second drain, a second gate, and a second well;

wherein the second drain, the second gate, the first source and the first well are coupled together;

wherein the second source and the second well are coupled to the first terminal; and

wherein the first drain and the first gate are coupled to the second terminal.

14. The circuit according to claim 8 , wherein the programming circuit comprises an active transistor feedback circuit.

15. A method of controlling a charge on a floating node between a capacitive sensor and an amplifier using a programming transistor having a source, a floating gate, and a drain, the method comprising:

applying a first predetermined voltage signal to the source of the programming transistor;

applying a second predetermined voltage signal to the floating gate of the programming transistor; and

applying a third predetermined voltage signal to the drain of the programming transistor until a charge on the floating gate of the programming transistor reaches a predetermined value,

wherein the charge on the floating gate of the programming transistor drives the charge on the floating node to the predetermined value.

16. A capacitive sensing circuit comprising:

a capacitive sensor having a sensor output;

a programming circuit having a programming circuit output coupled to the sensor output of the capacitive sensor; and

an amplifier having a first amplifier input and an amplifier output, the first amplifier input being coupled to the programming circuit output of the programming circuit;

the programming circuit comprising a pseudo resistor having a first terminal and a second terminal,

the pseudo resistor comprising:

a first transistor having a first source, a first drain, a first gate, and a first well;

a second transistor having a second source, a second drain, a second gate, and a second well;

wherein the second drain, the second gate, the first source and the first well are coupled together;

wherein the second source and the second well are coupled to the first terminal; and

wherein the first drain and the first gate are coupled to the second terminal.