Oscillator with MEMS resonator

1. A MEMS oscillator comprising:

a feedback-type oscillation circuit including a MEMS resonator and an amplifier;

a voltage control unit operable to control a bias voltage applied to an oscillating member of the MEMS resonator; and

an auto gain control unit operable to receive an output from the amplifier and to output, to the amplifier, based on a level of the output from the amplifier, an amplitude control signal for increasing or decreasing a gain of the amplifier such that the level of the output from the amplifier comes to be a predetermined level, for controlling the gain of the amplifier;

wherein the voltage control unit controls the bias voltage applied to the oscillating member of the MEMS resonator based on an operating temperature of the MEMS resonator such that a peak gain of the MEMS resonator comes to have a predetermined value regardless of a level of the operating temperature, and

the voltage control unit derives the operating temperature of the MEMS resonator, by monitoring the amplitude control signal.

2. A MEMS oscillator comprising:

a feedback-type oscillation circuit including a MEMS resonator and an amplifier;

a voltage control unit operable to control a bias voltage applied to an oscillating member of the MEMS resonator; and

an auto gain control unit operable to receive an output from the amplifier and to output, to the amplifier, based on a level of the output from the amplifier, an amplitude control signal for increasing or decreasing a gain of the amplifier such that the level of the output from the amplifier comes to be a predetermined level, for controlling the gain of the amplifier;

wherein the voltage control unit controls the bias voltage applied to the oscillating member of the MEMS resonator based on an operating temperature of the MEMS resonator such that a peak gain of the MEMS resonator comes to have a predetermined value regardless of a level of the operating temperature, and

the MEMS oscillator further includes a temperature sensor operable to measure the operating temperature of the MEMS resonator and to output a result of the measurement,

the result of the measurement of the operating temperature outputted from the temperature sensor is inputted to the voltage control unit, and the voltage control unit uses the result of the measurement as the operating temperature of the MEMS resonator.

3. The MEMS oscillator according to claim 1 , wherein

the MEMS oscillator performs control such that the peak gain of the MEMS resonator comes to have a predetermined value, regardless of the level of the operating temperature, by controlling the bias voltage applied to the oscillating member of the MEMS resonator through the voltage control unit or by controlling the auto gain control unit, based on the operating temperature of the MEMS resonator.

4. The MEMS oscillator according to claim 3 , wherein

the voltage control unit controls the bias voltage applied to the oscillating member of the MEMS resonator such that the peak gain of the MEMS resonator comes to have a predetermined value regardless of the level of the operating temperature, when the operating temperature of the MEMS resonator is higher than a predetermined temperature, and

the voltage control unit controls the bias voltage such that the bias voltage comes to have a constant value regardless of the level of the operating temperature and controls the auto gain control unit such that a level of a feed-back signal comes to be a predetermined level regardless of the level of the operating temperature, when the operating temperature of the MEMS resonator is lower than the predetermined temperature.

5. The MEMS oscillator according to claim 4 , wherein

when the operating temperature of the MEMS resonator is higher than a predetermined temperature, the voltage control unit performs control, in such a way as to cause the level of the feed-back signal to have the same value as that of a signal level at the predetermined temperature and as to increase the bias voltage to above the bias voltage at the predetermined temperature, and

when the operating temperature of the MEMS resonator is lower than a predetermined temperature, the voltage control unit performs control, in such a way as to cause the bias voltage to have the same value as the bias voltage at the predetermined temperature and to decrease the level of the feed-back signal to below the signal level at the predetermined temperature.

6. The MEMS oscillator according to claim 1 , further comprising:

a PLL frequency synthesizer unit operable to receive an output of the amplifier and to output an output signal; and

a frequency-division-ratio control unit operable to control a frequency division ratio of a programmable frequency divider placed in a feedback section in the PLL frequency synthesizer unit, based on the operating temperature of the MEMS resonator and the bias voltage applied to the oscillating member of the MEMS resonator,

wherein the frequency-division-ratio control unit controls the frequency division ratio of the programmable frequency divider, such that the output signal has a predetermined frequency, regardless of the levels of the operating temperature and the bias voltage.

7. The MEMS oscillator according to claim 2 , wherein

the MEMS oscillator performs control such that the peak gain of the MEMS resonator comes to have a predetermined value, regardless of the level of the operating temperature, by controlling the bias voltage applied to the oscillating member of the MEMS resonator through the voltage control unit or by controlling the auto gain control unit, based on the operating temperature of the MEMS resonator.

8. The MEMS oscillator according to claim 7 , wherein

the voltage control unit controls the bias voltage applied to the oscillating member of the MEMS resonator such that the peak gain of the MEMS resonator comes to have a predetermined value regardless of the level of the operating temperature, when the operating temperature of the MEMS resonator is higher than a predetermined temperature, and

the voltage control unit controls the bias voltage such that the bias voltage comes to have a constant value regardless of the level of the operating temperature and controls the auto gain control unit such that a level of a feed-back signal comes to be a predetermined level regardless of the level of the operating temperature, when the operating temperature of the MEMS resonator is lower than the predetermined temperature.

9. The MEMS oscillator according to claim 8 , wherein

when the operating temperature of the MEMS resonator is higher than a predetermined temperature, the voltage control unit performs control, in such a way as to cause the level of the feed-back signal to have the same value as that of a signal level at the predetermined temperature and as to increase the bias voltage to above the bias voltage at the predetermined temperature, and

when the operating temperature of the MEMS resonator is lower than a predetermined temperature, the voltage control unit performs control, in such a way as to cause the bias voltage to have the same value as the bias voltage at the predetermined temperature and to decrease the level of the feed-back signal to below the signal level at the predetermined temperature.

10. The MEMS oscillator according to claim 2 , further comprising:

a PLL frequency synthesizer unit operable to receive an output of the amplifier and to output an output signal; and

a frequency-division-ratio control unit operable to control a frequency division ratio of a programmable frequency divider placed in a feedback section in the PLL frequency synthesizer unit, based on the operating temperature of the MEMS resonator and the bias voltage applied to the oscillating member of the MEMS resonator,

wherein the frequency-division-ratio control unit controls the frequency division ratio of the programmable frequency divider, such that the output signal has a predetermined frequency, regardless of the levels of the operating temperature and the bias voltage.