MEMS oscillator
View Patent ↗Provided is a MEMS oscillation circuit which performs temperature compensation of a MEMS resonator with a simple circuit, which is mild so that an output clock does not have jitter, and which makes the range of fluctuations of a reference frequency from a reference value equivalent to a range of digital processing. The MEMS oscillator includes a MEMS resonator, a temperature measurement unit for measuring a temperature and outputting a detected voltage corresponding to the temperature, and a bias voltage control circuit for applying the MEMS resonator with a bias voltage which changes the resonant frequency of the MEMS resonator in a manner opposite to a change of the resonant frequency of the MEMS resonator due to temperature change correspondingly to the detected voltage.
1. An MEMS oscillator comprising:
an MEMS resonator configured to oscillate at a resonant frequency which is a function of a bias voltage applied to the MEMS resonator;
a temperature sensor configured to output a signal indicative of a temperature of the MEMS resonator, wherein the signal from the temperature sensor has a voltage that changes proportionally to a change of the temperature; and
a bias voltage controller configured to apply the bias voltage determined based on the signal from the temperature sensor,
wherein the bias voltage controller comprises an amplifier configured to translate a deviation of the voltage of the signal from a reference voltage into the bias voltage to compensate the change of the resonant frequency caused by the change of the temperature,
wherein the amplifier comprises:
a first input terminal to which the signal from the temperature sensor is supplied;
an output terminal connected to a reference voltage circuit via serially connected first and second resistors; and
a second input terminal connected to a joint between the first and second resistors,
wherein the reference voltage is a voltage at the joint, and the bias voltage is proportional to a difference between the voltage of the signal and the reference voltage multiplied by a ratio between the resistances of first and second resistors.
2. The MEMS oscillator according to claim 1 , wherein the temperature sensor comprises a constant current circuit and a diode serially connected to a ground, such that when the temperature rises, the constant current circuit flows more current through the diode, whereby the voltage of the signal drops, whereas when the temperature drops, the constant current circuit flows less current through the diode, whereby the voltage of the signal rises.
3. The MEMS oscillator according to claim 1 , wherein the bias voltage is inversely proportional to the voltage of the signal.
4. The MEMS oscillator according to claim 1 , wherein at least one of the first and second resistors is variable.
5. A method for compensating a change of a resonance frequency of an MEMS oscillator caused by a change of a temperature, comprising:
providing an MEMS resonator configured to oscillate at a resonant frequency which is a function of a bias voltage applied to the MEMS resonator;
measuring a temperature of the MEMS resonator and outputting a temperature signal indicative of the temperature of the MEMS resonator; and
applying the bias voltage determined based on the temperature signal to compensate the change of the resonant frequency caused by the change of the temperature,
wherein applying the bias voltage comprises:
translating a deviation of the voltage of the temperature signal supplied to a first amplifier input from a reference voltage supplied to a second amplifier input into the bias voltage supplied at an amplifier output, wherein the reference voltage is a voltage at a joint between first and second resistors connected serially between a reference voltage source and the amplifier output.
6. The method according to claim 5 , wherein outputting a temperature signal comprises outputting a temperature signal at a voltage which changes proportionally to a change of the temperature.
7. The method according to claim 6 , wherein outputting a temperature signal at a voltage comprises outputting a temperature signal at a voltage which drops when the temperature rises and rises when the temperature drops.
8. The method according to claim 6 , wherein applying the bias voltage further comprises applying the bias voltage which is proportional to the voltage of the temperature signal.
9. The method according to claim 8 , wherein the bias voltage is inversely proportional to the voltage of the temperature signal.
10. The method according to claim 5 , wherein applying the bias voltage further comprises applying the bias voltage proportional to a difference between the voltage of the signal and the reference voltage.