Method and apparatus for calibration of sensor signals

1. A method for providing calibration of capacitive sensor signals in a capacitive sensor having a capacitive measuring sensor and a capacitive reference sensor, the method comprising:

receiving a capacitive sensor signal and a capacitive reference signal from the capacitive measuring sensor and the capacitive reference sensor, respectively;

generating a first compensation signal to the sensor signal based on a gain characteristic wherein the gain circuit generates an output, Vout, obeying the following equation:

V out= Vdd *(1/β*( Cp−α R *Cr )/ Cp )

where:

Cp is a measured capacitance from the capacitive sensor;

Cr is a reference capacitance from the reference sensor;

α R is an offset component;

β is a gain component; and

Vdd is a supply voltage;

generating a second compensation signal to the reference signal based on the gain characteristic and an offset characteristic;

combining the first compensation signal and the capacitive sensor signal, and the second compensation signal and the capacitive reference signal to create a compensated sensor signal; and,

adjusting the compensated signal for temperature effects by coupling a component having a high thermal coefficient to the sensor.

2. The method of claim 1 , wherein providing the second compensation signal to the capacitive reference signal is further based on a linearity characteristic.

3. The method of claim 1 , wherein combining the first compensation signal and the capacitive sensor signal, and the second compensation signal and the capacitive reference signal to create the compensated sensor signal further comprises combining a temperature characteristic with the compensated sensor signal.

4. The method of claim 1 , further comprising adjusting the gain characteristic based on the compensated sensor signal.

5. The method of claim 1 , further comprising using the compensated signal as a feedback signal for compensating for temperature effects.

6. A sensing system comprising:

a capacitive sensor;

a reference sensor;

a clock generator,

an integration circuit, the integration circuit coupled to the capacitive sensor and the reference sensor, the integration circuit comprising a plurality of switches controlled by the clock generator to selectively combine a gain component and an offset component with outputs from the capacitive sensor and the reference sensor to generate an integrated output;

a gain circuit, the gain circuit receiving the integrated output, to combine a gain compensation therewith, the gain circuit including a resistor having a low temperature coefficient characteristic;

wherein the gain circuit generates an output, Vout, obeying the following equation:

V out= Vdd *(1/β*( Cp−α R *Cr )/ Cp )

where:

Cp is a measured capacitance from the capacitive sensor;

Cr is a reference capacitance from the reference sensor;

α R is an offset component;

β is a gain component; and

Vdd is a supply voltage.

7. The sensor system of claim 6 , wherein the gain circuit further including a component coupled thereto having a low temperature coefficient.

8. The sensor system of claim 6 , further comprising a capacitor coupled between the integration circuit and the gain circuit.

9. The sensor system of claim 6 , wherein the integration circuit further combines a linearity component with outputs from the capactive sensor and the reference sensor.

10. The sensor system of claim 6 , wherein the integration circuit selectively subtracts the gain component and the offset component from the supply voltage Vdd to generate the integrated output.

11. The sensor system of claim 6 , wherein the gain circuit further including an input to compensate for temperature.