MEMS Resonator DC Offset Compensation via Startup Glitch
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Solution Overview
Problem
The start-up of MEMS gyro devices is often hindered by electrostatic discharge (ESD) protection components that introduce a DC offset, preventing the comparator from switching and thus preventing the generation of a clock signal and drive signal, unless a low-frequency high-pass filter is used, which occupies valuable board or die space.
Innovation Solution
A system comprising a resonating sensor, a drive device, a variable gain charge amplifier, and a variable gain voltage amplifier, where the charge amplifier compensates for DC offset by generating a clock signal and using controllable gain switches to produce a glitch that overcomes the offset, allowing the resonator to reach a steady state operating mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ESD protection components are added to the charge amplifier input, then protection against electrostatic discharge is improved, but DC offset is introduced that prevents comparator switching
Solution Approach 1:
The system performs preliminary action by generating a startup glitch signal before normal operation begins. This glitch signal temporarily overrides the DC offset caused by ESD protection, allowing the comparator to switch and initiate oscillation. Once the resonator is running, the glitch is no longer needed, thus resolving the contradiction between ESD protection and comparator switching capability.
Solution Approach 2:
The system uses periodic action through the oscillation generation process. The comparator switches periodically to generate clock signals that drive the resonator. The startup glitch initiates this periodic switching by temporarily creating a voltage difference that overcomes the DC offset, enabling the resonator to reach a state where natural periodic oscillation can occur.
2Ease of operation
If a low frequency high pass filter is added to overcome DC offset, then comparator switching is enabled, but board space or die space is consumed
Solution Approach 1:
The system extracts the DC offset compensation function from the physical high-pass filter circuit and implements it through signal processing. Instead of using a separate filter component that would occupy board space, the glitch generation circuitry integrates the offset compensation function into the existing signal path, allowing the comparator to switch without requiring additional physical space.
Solution Approach 2:
The system replaces the mechanical/electrical high-pass filter with an electronic signal processing approach. Rather than using passive filter components (resistors, capacitors) that occupy physical space, the solution uses active circuitry to generate a glitch signal that electronically compensates for the DC offset, substituting a physical filter with an electronic control mechanism.
3Ease of operation
If a low frequency high pass filter is added to overcome DC offset, then comparator switching is enabled, but die space within ASIC is consumed
Solution Approach 1:
The system merges the DC offset compensation function with the existing charge amplifier and comparator circuitry. The glitch generation is integrated into the signal path rather than being a separate function, combining multiple operations (amplification, offset compensation, and comparison) into a unified circuit that minimizes die space while enabling comparator switching.
Solution Approach 2:
The circuit components serve multiple functions: the charge amplifier not only amplifies the sensor signal but also generates the startup glitch signal; the comparator performs both the switching function and the detection of resonator oscillation. This multi-functionality reduces the need for dedicated components, thereby minimizing die space while maintaining the ability to overcome DC offset.
Data Source
AI summary
Systems and methods for insuring successful initiation of a resonating micro-electro mechanical systems (MEMS). An example system includes a resonating sensor, a drive device, a charge amplifier, and a voltage gain circuit. At start up, the charge amplifier and voltage gain circuit receives signals from the resonating sensor, compensates this signal for DC offsets, and generates a clock signal for the drive, thus placing the resonating sensor in a steady state operating mode. The circuit includes a plurality of gain switches that are toggled to produce a glitch in the signal associated with the received signal. The glitch overcomes the DC offset. A comparator generates the clock signal for the drive device if a signal associated with the received signal exceeds a reference signal.