Vibration gyro sensor

1. A vibration gyro sensor, comprising:

a vibrating element;

a pair of drive electrodes for driving the vibrating element;

at least two detection electrodes for detecting Coriolis force applied to the vibrating element;

a monitor circuit coupled with one of the pair of drive electrodes, so as to output a monitor signal;

a drive circuit for amplifying the monitor signal so as to output an amplified signal to the other of the pair of drive electrodes;

a differential amplifier circuit for differentially amplifying at least two signals obtained from the detection electrodes of the vibrating element, so as to output a differential amplified signal;

a synchronous detection circuit for synchronously detecting the differential amplified signal with respect to the monitor signal, so as to output a detected signal;

a filter circuit for outputting a filtered signal in which a noise of the detected signal is removed; and

a ratiometric circuit which receives the filtered signal and outputs a sensitivity signal whose amplitude is proportional to variation of a power voltage.

2. The vibration gyro sensor according to claim 1 , wherein the ratiometric circuit and a circuit which is previous to the filter circuit receive a common power source.

3. The vibration gyro sensor according to claim 2 , wherein the filter circuit is a passive low-pass filter.

4. A vibration gyro sensor, comprising:

a vibrating element;

a pair of drive electrodes for driving the vibrating element;

at least two detection electrodes for detecting Coriolis force applied to the vibrating element;

a monitor circuit coupled with one of the pair of drive electrodes, so as to output a monitor signal;

a drive circuit for amplifying the monitor signal so as to output an amplified signal to the other of the pair of drive electrodes;

a differential amplifier circuit for differentially amplifying at least two signals obtained from the detection electrodes of the vibrating element, so as to output a differential amplified signal;

a synchronous detection circuit for synchronously detecting the differential amplified signal with respect to the monitor signal, so as to output a detected signal;

a filter circuit for outputting a filtered signal in which .a noise of the detected signal is removed; and

a ratiometric circuit which receives the filtered signal and outputs a sensitivity signal whose amplitude is proportional to variation of a power voltage;

a first power circuit for supplying a first power source to the filter circuit;

a second power circuit for supplying a second power source to the ratiometric circuit;

a first reference voltage generation circuit which receives the first power source and supplies a first reference voltage to a circuit being previous to the ratiometric circuit; and

a second reference voltage generation circuit which receives the second power source and supplies a second reference voltage to the ratiometric circuit.

5. The vibration gyro sensor according to claim 4 , wherein the filter circuit is an active low-pass filter driven by the first power source.

6. The vibration gyro sensor according to claim 1 , wherein the vibrating element is a double-T shaped vibrating element.

7. The vibration gyro sensor according to claim 1 , wherein the filter circuit includes an n-th order filter, where n is greater than or equal to 2.

8. The vibration gyro sensor according to claim 1 , wherein the filter circuit is immediately previous to the ratiometric circuit.

9. The vibration gyro sensor according to claim 1 , wherein the ratiometric circuit includes a multiplier.

10. The vibration gyro sensor according to claim 1 , further comprising a voltage generation circuit that generates a reference voltage based on the power voltage,

wherein the reference voltage is proportional to the power voltage; and

wherein the ratiometric circuit multiplies the reference voltage by an amplitude of the filtered signal to generate the sensitivity signal.