Pseudo-differential accelerometer EMI rejection via chopper modulation
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Solution Overview
Problem
Capacitive sensors in inertial sensors face significant challenges due to electromagnetic interference (EMI) from capacitive coupling with bond wires and nearby electronics, which can obscure desired sensor signals, especially in high-density electronic environments, and existing solutions like shielding and differential approaches are either bulky or difficult to maintain effectively.
Innovation Solution
A pseudo-differential accelerometer design that uses a microelectromechanical device connected to an integrated circuit with a chopper system, differential amplifier, dummy core, and neutralization core, which reduces the number of bond wires and smears noise across a wide frequency range, effectively mitigating EMI and feed-through capacitance nonlinearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If shielding the sensor with metal is used to block EMI, then electromagnetic interference rejection is improved, but device size and cost increase
Solution Approach 1:
The patent replaces the mechanical/physical shielding approach (metal Faraday cage) with an electronic signal processing approach. The chopper system modulates sensor signals to higher frequencies where EMI has less impact, and the differential amplifier electronically subtracts common-mode EMI noise from differential sensor signals, achieving EMI rejection without additional physical shielding structures.
Solution Approach 2:
The patent changes the frequency parameter of sensor signals using the chopper system. By modulating DC or low-frequency sensor signals to higher AC frequencies, the system moves sensor signals away from the DC component where EMI is most problematic, thereby improving EMI rejection without requiring physical shielding.
2Object-affected harmful factors
If a differential approach with closely matched disturbance capacitances is used to reject EMI, then electromagnetic interference rejection is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent uses feedback through the chopper system to actively compensate for EMI effects. The chopper modulates the sensor signals and uses the differential amplifier's feedback mechanism to continuously adjust and cancel common-mode EMI noise, reducing the need for precise initial capacitance matching between sensor elements.
Solution Approach 2:
The patent introduces dynamic signal modulation through the chopper system, which actively adapts to and cancels time-varying EMI noise. This dynamic approach replaces the static requirement for precisely matched capacitances with an active compensation mechanism that adjusts in real-time to EMI conditions.
3Adaptability or versatility
If numerous bond wires are used to connect sensor cores, then sensor functionality is improved, but area requirements for connections increase
Solution Approach 1:
The patent merges multiple sensor cores into a single integrated capacitive sensor structure with shared bond wire connections. By combining the functionality of multiple cores and using common bond wires to connect to the ASIC, the design reduces the total number of bond wires and connection pads required while maintaining full sensor functionality through the integrated pseudo-differential architecture.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The pseudo-differential accelerometer design significantly reduces electromagnetic interference, maintains signal linearity, and requires fewer bonding pads and bond wires, enhancing robustness and reducing area requirements for connections while minimizing nonlinearity due to feed-through capacitances.
Implementation Method 1
The chopper system has a plurality of chopper inputs and a plurality of chopper outputs, wherein during a chop state 0 the chopper system connects a first set of the plurality of chopper inputs to a first set of the plurality of chopper outputs and during a chop state 1 the chopper system connects a second set of the plurality of chopper inputs to a second set of the plurality of chopper outputs
Implementation Method 2
The differential approach takes the differences between signals on parallel wires which can substantially subtract out the electromagnetic disturbance as a common mode signal
Implementation Method 3
A source of EMI 110 that is near the bond wires 106 creates capacitive coupling 112 between the EMI source 110 and the bond wires 106
Implementation Method 4
For this reason additional techniques can be used to smear the EMI energy over a wide frequency range
Data Source
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AI summary
A pseudo-differential accelerometer resistant to EMI is disclosed that includes a device with a sensor core connected to an integrated circuit including a chopper, differential amplifier, and dummy core. The chopper swaps input to output connections during different states. The dummy core is coupled to a dummy chopper input. Three bond wires coupling the sensor output to a sensor chopper input, a first chopper output to a first sensor input, and a second chopper output to a second sensor input can connect the sensor and integrated circuit. The device can include a dummy pad and dummy bond wire connecting the dummy pad to the dummy chopper input. This configuration requires four bond wires connecting the sensor and integrated circuit. A neutralization core can be connected to the sensor chopper input. The chopper can change states to smear noise across a wide range, or away from a band of interest.