Combination sensor

1. A combination sensor, comprising:

a pressure sensor having an actuator which has a first resonant frequency;

a cavity, coupled to the pressure sensor and able to receive a substance;

wherein the cavity, in an absence of the substance, has a second resonant frequency in response to excitation by the actuator;

wherein the cavity, in a presence of the substance, has a third resonant frequency in response to excitation by the actuator;

wherein the first resonant frequency differs from the second and third resonant frequencies;

a sensor circuit including a driver module configured to excite the actuator, an actuator power level monitor and a detection module,

wherein the detection module is configured to output a substance detected signal in response to the third resonant frequency in the cavity;

wherein the sensor circuit is embedded within a semiconductor chip covered by an overmolding layer, wherein the cavity is an opening within the overmolding layer, wherein the opening has a width, a height, and a length, and

wherein the first, second and third cavity resonant frequencies are based on the width, height and length of the overmolding layer opening.

2. The combination sensor of claim 1 :

wherein the first resonant frequency is higher than the second and third resonant frequencies.

3. The combination sensor of claim 1 :

wherein the second and third resonant frequencies depend upon a speed of sound in the substance.

4. The combination sensor of claim 1 :

wherein the cavity includes a physical dimension such that the third resonant frequency indicates presence of a target substance.

5. The combination sensor of claim 1 :

wherein the substance is at least one from a group consisting of: a gas, carbon dioxide, a liquid, a solid, a plasma, a molecule, a pathogen, an aerosol, a particulate concentration, pollution and a mixture of the aforementioned substances.

6. The combination sensor of claim 1 :

wherein a pressure wave in the cavity can be created in response to power from the sensor circuit.

7. The combination sensor of claim 1 :

wherein the sensor circuit includes an actuator power level monitor and a detection module;

wherein the detection module includes a first threshold power level and outputs the substance detected signal if a monitored actuator power level at the third resonant frequency is below the first threshold power level.

8. The combination sensor of claim 7 :

wherein the detection module includes a second threshold power level and outputs a substance not detected signal if the monitored actuator power level at the second resonant frequency is below the second threshold power level.

9. The combination sensor of claim 1 :

wherein the sensor circuit includes an actuator power level monitor, a detection module and a driver module;

wherein the driver module includes a frequency generator which excites the actuator and includes a circuit capable of varying the excitation frequency of the actuator over a range of frequencies; and

wherein the detection module includes a circuit for detecting a frequency where a monitored actuator power level is near a minimum.

10. The combination sensor of claim 1 :

wherein the sensor circuit includes a frequency generator;

wherein the frequency generator excites the actuator; and

wherein the frequency generator does not excite the actuator while the sensor circuit is using the pressure sensor to monitor a pressure in the cavity.

11. The combination sensor of claim 1 :

wherein the combination sensor is formed at least in part from at least one from a group consisting of: bulk wafer material, wafer surface material deposition, overmolding, packaging, a MEMS device and a CMOS device.

12. The combination sensor of claim 1 :

wherein the pressure sensor includes a capacitive pressure sensor membrane; and

wherein the actuator is the capacitive pressure sensor membrane.

13. The combination sensor of claim 1 :

further comprising a gas-permeable membrane coupled to cover a side of the cavity substantially opposite to the pressure sensor.

14. The combination sensor of claim 1 :

wherein the combination sensor is part of at least one from a group consisting of: a CO2 monitoring system, an indoor monitoring system, a food quality monitoring system, an air quality control system, and a mobile device.

15. A combination gas pressure sensor and carbon dioxide level sensor, comprising:

a cavity, coupled to the pressure sensor and coupled to expose the cavity and the pressure sensor to a gas;

wherein the gas pressure sensor includes a membrane;

wherein the cavity has a predetermined resonant frequency in response to excitation by the membrane when carbon dioxide is in the cavity;

a sensor circuit including a driver module configured to excite the membrane, a membrane power level monitor and a detection module,

wherein the detection module is configured to output a carbon dioxide detected signal in response to the predetermined resonant frequency in the cavity,

wherein the sensor circuit is embedded within a semiconductor chip covered by an overmolding layer,

wherein the cavity is an opening within the overmolding layer,

wherein the opening has a width, a height, and a length, and

wherein the predetermined resonant frequency is based on the width, height and length of the overmolding layer opening.

16. An article of manufacture comprising at least one non-transitory, tangible machine readable storage medium containing executable machine instructions for operating a combination sensor, the instructions comprising:

exciting an actuator in a pressure sensor coupled to a cavity over a range of frequencies;

monitoring a power level required to excite the actuator;

comparing the actuator power level, at a predetermined frequency dependent upon the cavity dimensions, to a threshold power level; and

outputting a substance detected signal if the monitored actuator power level at the predetermined frequency is below the threshold power level;

wherein the combination sensor includes a sensor circuit having a driver module configured to excite the actuator, an actuator power level monitor and a detection module;

wherein the detection module is configured to output the substance detected signal;

wherein the sensor circuit is embedded within a semiconductor chip covered by an overmolding layer,

wherein the cavity is an opening within the overmolding layer,

wherein the opening has a width, a height, and a length and defines the cavity dimensions, and

wherein the predetermined frequency is based on the width, height and length of the overmolding layer opening.

17. The instructions of claim 16 :

wherein monitoring includes:

measuring an impedance of the actuator; and

identifying a frequency within the range having a minimum impedance; and

wherein outputting includes outputting the substance detected signal if the minimum impedance is below a threshold impedance level.

18. The instructions of claim 16 :

wherein the substance is a mixture containing carbon dioxide gas.

19. The instructions of claim 16 :

wherein the monitored actuator power level is below the threshold power level at a resonant frequency of the cavity.