MEMS Sensor Stabilization Circuit for Negative Input Resistance
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Solution Overview
Problem
Microelectromechanical systems (MEMS) sensors with capacitive MEMS motors can experience oscillations due to negative input resistance in the amplifier input stage, leading to instability.
Innovation Solution
A stabilization circuit is introduced to inject a compensation current at the input of the amplifier input stage, offsetting the negative real part of the input current and stabilizing the circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a source follower amplifier input stage is used with a high-Q MEMS motor, then the amplifier can condition the signal from the MEMS motor, but the circuit becomes unstable and oscillates due to negative input resistance
Solution Approach 1:
The patent converts the harmful negative input resistance effect into a beneficial stabilization mechanism by introducing a feedback circuit that senses the negative resistance effect and applies compensating action. The stabilization circuit uses the information about the negative resistance to generate a compensating signal that cancels the harmful effect, turning the instability problem into a controlled stabilization solution.
Solution Approach 2:
The patent implements a feedback-based stabilization circuit that monitors the input stage conditions and adjusts the circuit parameters to maintain stability. The feedback mechanism detects the negative input resistance effect and applies corrective action through a controlled feedback path, allowing the system to automatically compensate for the instability caused by the source follower input stage.
2Ease of operation
If the real part of the amplifier input impedance is negative, then the amplifier input stage can provide signal conditioning, but the sum of series resistance and input resistance becomes negative causing oscillation
Solution Approach 1:
The patent dynamically changes the circuit parameters by introducing a stabilization circuit that adjusts the effective input impedance. The stabilization circuit modifies the real part of the input impedance through controlled parameter adjustment, transforming the negative resistance condition into a positive or less negative resistance condition, thereby preventing oscillation while preserving signal conditioning capability.
Data Source
AI summary
A microelectromechanical systems (MEMS) sensor, a capacitive MEMS motor sensing circuit and a method are provided. The MEMS sensor includes a housing having electrical contacts disposed on an exterior of the housing. The MEMS sensor further includes a capacitive MEMS motor disposed in the housing, and an electrical circuit disposed in the housing and being electrically coupled to the electrical contacts. The electrical circuit includes a bias voltage source having an output coupled to an input of the MEMS motor. The electrical circuit further includes an amplifier including an amplifier input stage having an input, coupled to an output of the MEMS motor, the amplifier input stage having a negative input resistance, where a sum of a series resistance of the MEMS motor at the input and the negative input resistance is less than zero, and wherein application of a signal from the output of the MEMS motor to the input of the amplifier input stage produces a negative real part of input current. The electrical circuit still further includes a stabilization circuit having an output coupled to the input of the amplifier input stage, where the stabilization circuit injects a compensation current at the input of the amplifier input stage that offsets at least a portion of the negative real part of input current.