Integrated MEMs inertial sensing device with automatic gain control
An integrated MEMS inertial sensing device can include a MEMS inertial sensor with a drive loop configuration overlying a CMOS IC substrate. The CMOS IC substrate can include an AGC loop circuit coupled to the MEMS inertial sensor. The AGC loop acts in a way such that generated desired signal amplitude out of the drive signal maintains MEMS resonator velocity at a desired frequency and amplitude. A benefit of the AGC loop is that the charge pump of the HV driver inherently includes a ‘time constant’ for charging up of its output voltage. This incorporates the Low pass functionality in to the AGC loop without requiring additional circuitry.
1. An integrated MEMS inertial sensing device, the device comprising:
a substrate member having a surface region;
a CMOS IC layer overlying the surface region, the CMOS IC layer having a CMOS surface region, the CMOS IC layer having an Automatic Gain Control (AGC) loop circuit, the AGC loop circuit including
a rectifier,
a proportional-integral-derivative (PID) controller, an input of the PID controller being electrically connected to an output of the rectifier,
a comparator having an input electrically connected to an output of the PID controller,
a charge pump having an input electrically connected to an output of the comparator, and
a high-voltage (HV) driver having an input electrically connected to an output of the charge pump; and
a MEMS inertial sensor overlying the CMOS surface region, the MEMS inertial sensor electrically coupled to the AGC loop circuit.
2. The integrated MEMS inertial sensing device of claim 1 wherein the PID controller includes an integrator and a differentiator, wherein the integrator uses a programmable time constant to determine a variable operational speed of the AGC loop circuit, and wherein the differentiator is configured to change a current for charging and discharging a capacitor in the charge pump in the start-up duration so the time constant is reduced and the capacitor voltage changes faster to reduce a start-up time of the AGC loop circuit.
3. The integrated MEMS inertial sensing device of claim 1 wherein the PID controller is configured to output a differential PWM signal having a PWM signal and an inverted PWM signal, and wherein the output of the charge pump is configured to be proportional to a duty cycle of the PWM signal.
4. The integrated MEMS inertial sensing device of claim 3 wherein the charge pump is a first charge pump, and the AGC loop further comprises a second charge pump coupled to a charge pump node, wherein a first current source is coupled to the charge pump node, the PWM signal, and a supply voltage, and wherein a second current source is coupled to the charge pump node, the inverted PWM signal, and ground.
5. The integrated MEMS inertial sensing device of claim 4 further comprising a charge pump capacitor coupled to the charge pump node, the second charge pump, the first and second current sources, and the charge pump capacitor being configured to maintain a desired voltage on the charge pump node.
6. The integrated MEMS inertial sensing device of claim 1 further comprising a triangle wave generator coupled to the comparator and configured to generate triangular pulses, wherein the output of the PID is compared to the triangular pulses by the comparator.
7. The integrated MEMS inertial sensing device of claim 1 wherein the charge pump is configured as a power supply to the HV driver.
8. An integrated MEMS inertial sensing device, the device comprising:
a substrate member having a surface region;
a CMOS IC layer overlying the surface region, the CMOS IC layer having a CMOS surface region, the CMOS IC layer having an Automatic Gain Control (AGC) loop circuit, the AGC loop circuit including
a rectifier,
a proportional-integral-derivative (PID) controller, an input of the PID controller being electrically connected to an output of the rectifier,
a comparator having an input electrically connected to an output of the PID controller,
a charge pump having an input electrically connected to an output of the comparator, and
a high-voltage (HV) driver having an input electrically connected to an output of the charge pump; and
a MEMS inertial sensor overlying the CMOS surface region, the MEMS inertial sensor electrically coupled to the AGC loop circuit through a driver resonator in the AGC loop;
wherein the PID controller includes an integrator and a differentiator, wherein the integrator uses a programmable time constant to determine a variable operational speed of the AGC loop circuit, and wherein the differentiator is configured to change a current for charging and discharging a capacitor in the charge pump in the start-up duration so the time constant is reduced and the capacitor voltage changes faster to reduce a start-up time of the AGC loop circuit.
9. The integrated MEMS inertial sensing device of claim 8 further comprising a mixer coupled to the MEMS inertial sensor, wherein the mixer is configured as a transmission gate.
10. The integrated MEMS inertial sensing device of claim 9 further comprising a circuit loop including a digital low-pass-filter (LPF) coupled to a digital/analog converter (DAC), the circuit loop being coupled to the mixer.
11. The integrated MEMS inertial sensing device of claim 8 further comprising a programmable phase-shifter (PS) coupled to the comparator.
12. The integrated MEMS inertial sensing device of claim 8 wherein the comparator is a first comparator, and further comprising a quadrature mode circuit including a second comparator and a multiplexer, wherein the quadrature mode circuit is configured to monitor a quadrature signal from the MEMS inertial sensor.
13. The integrated MEMS inertial sensing device of claim 8 further comprising a digital delay module coupled to the comparator and the HV driver, the digital delay module being configured to lock into a desired frequency.
14. The integrated MEMS inertial sensing device of claim 8 further comprising metal shielding within a vicinity of the MEMS inertial sensor, the metal shielding being configured to reduce parasitic effects.
15. An integrated MEMS inertial sensing device, the device comprising:
a substrate member having a surface region;
a CMOS IC layer overlying the surface region, the CMOS IC layer having a CMOS surface region, the CMOS IC layer having an Automatic Gain Control (AGC) loop circuit, the AGC loop circuit including
a rectifier,
a proportional-integral-derivative (PID) controller, an input of the PID controller being electrically connected to an output of the rectifier,
a comparator having an input electrically connected to an output of the PID controller,
a charge pump having an input electrically connected to an output of the comparator, and
a high-voltage (HV) driver having an input electrically connected to an output of the charge pump; and
a MEMS inertial sensor overlying the CMOS surface region, the MEMS inertial sensor electrically coupled to the AGC loop circuit;
wherein the PID controller includes an integrator and a differentiator, wherein the integrator uses a programmable time constant to determine a variable operational speed of the AGC loop circuit, and wherein the differentiator is configured to change a current for charging and discharging a capacitor in the charge pump in the start-up duration so the time constant is reduced and the capacitor voltage changes faster to reduce a start-up time of the AGC loop circuit; and
wherein the PID controller is configured to output a differential PWM signal having a PWM signal and an inverted PWM signal, and wherein the output of the charge pump is configured to be proportional to a duty cycle of the PWM signal.
16. The integrated MEMS inertial sensing device of claim 15 wherein the charge pump is a first charge pump, and further comprising a second charge pump coupled to a charge pump node, wherein a first current source is coupled to the charge pump node, the PWM signal, and a supply voltage, and wherein a second current source is coupled to the charge pump node, the inverted PWM signal, and ground.
17. The integrated MEMS inertial sensing device of claim 16 further comprising a charge pump capacitor coupled to the charge pump node, the second charge pump, the first and second current sources, and the charge pump capacitor being configured maintain a desired voltage on the charge pump node.
18. The integrated MEMS inertial sensing device of claim 15 further comprising a triangle wave generator coupled to the comparator and configured to generate triangular pulses, wherein the output of the PID is compared to the triangular pulses by the comparator.
19. The integrated MEMS inertial sensing device of claim 15 wherein the charge pump is configured as a power supply to the HV driver.