Pressure sensor using MEMS resonator
View Patent ↗A pressure sensor including: a MEMS resonator; a sweeping unit which sweeps a frequency of an excitation signal in a predetermined direction of sweeping, over a predetermined frequency range including a resonance frequency f 0 of a vibrator in the MEMS resonator, while outputting the excitation signal to the MEMS resonator; an integrating unit which inputs a vibrating-state information signal as a characteristic amount indicative of a vibrating state of the vibrator from the MEMS resonator while the sweeping unit sweeps the frequency, integrates a plurality of the vibrating-state information signals at different frequencies of the excitation signal, and outputs the integrated value; and a conversion unit adapted to determine a pressure acting on the MEMS resonator, based on the integrated value.
1. A pressure sensor employing a MEMS resonator, comprising:
a MEMS resonator;
a sweeping unit which sweeps a frequency of an excitation signal in a predetermined direction of sweeping, over a predetermined frequency range including a resonance frequency f 0 of a vibrator in the MEMS resonator, while outputting the excitation signal to the MEMS resonator;
an integrating unit which inputs a vibrating-state information signal as a characteristic amount indicative of a vibrating state of the vibrator from the MEMS resonator while the sweeping unit sweeps the frequency, integrates a plurality of the vibrating-state information signals at different frequencies of the excitation signal, and outputs the integrated value; and
a conversion unit which determines a pressure acting on the MEMS resonator, based on the integrated value.
2. The pressure sensor according to claim 1 , wherein
the integrating unit determines the integrated value, by integrating at least two vibrating-state information signals including a vibrating-state information signal of when the excitation signal has a frequency earlier than the resonance frequency f 0 in the direction of sweeping, and a vibrating-state information signal of when the excitation signal has a frequency later than the resonance frequency f 0 in the direction of sweeping.
3. The pressure sensor according to claim 2 , wherein
the MEMS resonator comprises a capacitance-type MEMS resonator, and
the sweeping unit performs the sweeping in such a direction that the frequency of the excitation signal is gradually lowered, from a sweeping starting frequency f 1 which is a frequency equal to or higher than the resonance frequency f 0 , to a sweeping completion frequency f 2 which is a frequency lower than the resonance frequency f 0 .
4. The pressure sensor according to claim 3 , wherein
the vibrator in the capacitance-type MEMS resonator is surrounded by an ambient atmosphere at a pressure equal to the pressure acting on the MEMS resonator, and
the conversion unit determines a Q factor of the MEMS resonator based on the integrated value and determines the pressure based on the determined Q factor.
5. The pressure sensor according to claim 3 , wherein
the capacitance-type MEMS resonator includes:
a vibrator;
an electrode disposed in such a way as to interpose a gap between the electrode and the vibrator; and
a mechanism which changes a size of the gap according to the magnitude of the pressure acting on the capacitance-type MEMS resonator, and
the conversion unit determines the size of the gap based on the integrated value and determines the pressure based on the determined size of the gap.
6. The pressure sensor according to claim 2 , wherein
the vibrating-state information signal comprises a signal including information about a vibration amplitude of the vibrator.
7. The pressure sensor according to claim 2 , wherein
the vibrating-state information signal comprises a signal including information about a vibrating speed of the vibrator.
8. The pressure sensor according to claim 2 , wherein
the vibrating-state information signal comprises a signal including information about an angle of flexure in the vibrator along with vibrating motion of the vibrator.
9. The pressure sensor according to claim 3 , wherein
an absolute value of the difference between the sweeping starting frequency f 1 and the sweeping completion frequency f 2 is preliminarily determined, based on the product of a temperature characteristic of the elastic modulus of the vibrator and a temperature changing range expected in a pressure-sensor-use environment.
10. The pressure sensor according to claim 2 , wherein
the MEMS resonator comprises a non-capacitance-type MEMS resonator, and
the sweeping unit performs the sweeping in such a direction that the frequency of the excitation signal is gradually heightened, from a sweeping starting frequency f 1 which is a frequency equal to or lower than the resonance frequency f 0 , to a sweeping completion frequency f 2 which is a frequency higher than the resonance frequency f 0 .