Drive circuitry and method for a vibration gyroscope
A drive circuitry for a vibration gyroscope is described. The drive circuitry comprises a digital phase shifter, a variable gain amplifier and a pulse signal generator arranged to generate a digital pulse signal having a frequency substantially equal to a drive frequency of the vibration gyroscope. A controller is arranged to connect drive actuation units of the vibration gyroscope to outputs of the pulse signal generator during a first start-up time period, to outputs of the digital phase shifter during a second start-up time period, and to outputs of the variable gain amplifier during a measurement time period. Furthermore, a vibration gyroscope device and a method of driving a vibration gyroscope are described.
1. A drive circuitry for a vibration MEMS gyroscope, the drive circuitry comprising:
a capacitance-to-voltage converter arranged to provide a drive measurement voltage signal indicative of a displacement of a gyroscope mass along a drive axis of the vibration gyroscope;
a threshold detector coupled to the capacitance-to-voltage converter to receive the drive measurement voltage signal and arranged to perform a threshold detection on the drive measurement voltage signal to obtain a first digital signal;
a digital phase shifter coupled to the threshold detector to receive the first digital signal and arranged phase shift the first digital to signal to obtain a second digital signal;
an integrator coupled to the capacitance-to-voltage converter to receive the drive measurement voltage signal and arranged to integrate the drive measurement signal to obtain an integrated drive measurement voltage signal;
a variable gain amplifier coupled to the integrator to receive the integrated drive measurement voltage signal and arranged to provide a drive actuation signal using the integrated drive measurement voltage signal and an amplifier gain control reference signal;
a pulse signal generator arranged to generate a digital pulse signal having a frequency substantially equal to a drive frequency of the vibration gyroscope;
a controller arranged to connect drive actuation units of the vibration gyroscope to outputs of:
the pulse signal generator during a first start-up time period for allowing drive actuation units to receive the digital pulse signal from the pulse signal generator during the first start-up time period,
the digital phase shifter during a second start-up time period following the first start-up time period for allowing the drive actuation units to receive the second digital signal from the digital phase shifter during the second start-up time period, and
the variable gain amplifier during a measurement time period following the second start-up time period for allowing the drive actuation units to receive the drive actuation signal from the variable gain amplifier during a measurement time period.
2. A drive circuitry according to claim 1 , comprising a voltage supply unit arranged to deliver a supply voltage to a primary resonator of the vibration gyroscope, and wherein the controller is arranged to control the voltage supply unit so as to:
set the supply voltage to a nominal level during the measurement time period;
set the supply voltage to a start-up level during the first start-up time period, the start-up level being higher than the nominal level.
3. A drive circuitry according to claim 2 , wherein the controller is arranged to:
keep the supply voltage at the start-up level during at least part of the second start-up time period.
4. A drive circuitry according to claim 3 , wherein the controller is arranged to:
keep the supply voltage at the start-up level during the complete second start-up time period.
5. A drive circuitry according to claim 2 , wherein the controller is arranged to:
receive the drive measurement voltage signal from the capacitance-to-voltage converter;
compare the drive measurement voltage signal with a target value during the second start-up time period;
decrease a charge pump voltage from the start-up level to the nominal level when the drive measurement voltage signal has reached the target value.
6. A drive circuitry according to claim 5 , wherein the controller is arranged to:
after decreasing the charge pump voltage from the start-up level to the nominal level, keep comparing the drive measurement voltage signal with the target value until the drive measurement voltage signal has reached the target value again at an end time of the second start-up time period;
connect the drive actuation units of the vibration gyroscope to outputs of the variable gain amplifier at the end time of the second start-up time period.
7. A drive circuitry according to claim 1 , wherein the circuitry comprises an amplifier module arranged to amplify the digital pulse signal or the second digital signal to obtain an amplified digital pulse signal having an amplitude that is higher than an amplitude of the drive actuation signal.
8. A drive circuitry according to claim 7 , wherein the amplitude of the amplified digital pulse signal lies between 3.0-4.0 Volts.
9. A drive circuitry according to claim 1 , wherein the charge pump is arranged to create a first and second charge pump voltage, the first charge pump voltage lying between 8.0-9.0 V, and the second charge pump voltage lying between 6.0-7.0 V.
10. An apparatus comprising a vibration MEMS gyroscope device according to claim 9 .
11. A vibration MEMS gyroscope device comprising a vibration gyroscope and a drive circuitry according to claim 1 .
12. A semiconductor device comprising a vibration MEMS gyroscope device according to claim 11 .
13. A semiconductor device comprising a drive circuitry according to claim 1 .
14. A method of driving a vibration MEMS gyroscope, the method comprising:
generating a digital pulse signal having a frequency substantially equal to a drive frequency of the vibration gyroscope;
applying the digital pulse signal to the drive actuation units of the vibration gyroscope during a first start-up time period;
obtaining a drive measurement voltage signal indicative of a displacement of a gyroscope mass along a drive axis of the vibration gyroscope;
performing a threshold detection on the drive measurement voltage signal to obtain a first digital signal;
phase shifting the first digital signal to obtain a second digital signal;
integrating the drive measurement signal to obtain an integrated drive measurement voltage signal;
generating a drive actuation signal using the integrated drive measurement voltage signal and a reference signal;
applying the second digital signal to the drive actuation units of the vibration gyroscope during a second start-up time period following the first start-up time period, and
applying the drive actuation signal to the drive actuation units of the vibration gyroscope during a measurement time period following the second start-up time period.
15. A method according to claim 14 , further comprising:
setting a supply voltage for a primary resonator of the vibration gyroscope to a start-up level during the first start-up time period;
setting the supply voltage to a nominal level during the measurement time period, the start-up level being higher than the nominal level.
16. A method according to claim 15 , further comprising:
keeping a charge pump voltage at the start-up level during at least part of the second start-up time period.
17. A method according to claim 15 , further comprising:
comparing the drive measurement voltage signal with a target value during the second start-up time period;
decreasing the charge pump voltage from the start-up level to the nominal level when the drive measurement voltage signal has reached the target value.