Scheme to achieve robustness to electromagnetic interference in inertial sensors

摘要

A capacitive sensor system and method resistant to electromagnetic interference is disclosed. The system includes a capacitive core, differential amplifier with inverting and non-inverting inputs, capacitive paths, and chopping system. Core can include inputs and outputs coupled to variable capacitors, and common nodes coupling variable capacitors. Capacitive paths couple core outputs to amplifier inputs. When chopping system is high, one polarity voltage is applied to core inputs, a first core output is coupled to the inverting input and a second core output is coupled to the non-inverting input. When the chopping system is low, opposite polarity voltage is applied to core inputs, and core output to amplifier input couplings are flipped. Capacitive paths can include bond wires. Chopping system can be varied between high and low at frequencies that smear noise away from a frequency band of interest, or that smear noise substantially evenly across a wide frequency range.

主权项

1. A capacitive sensor system resistant to electromagnetic interference, the capacitive sensor system comprising:
a capacitive core including a first variable capacitor, a second variable capacitor, a first core output coupled to the first variable capacitor, a second core output coupled to the second variable capacitor, and a common node coupling the first variable capacitor and the second variable capacitor; a differential amplifier including an inverting input and a non-inverting input; a first capacitive path between the first core output and the inputs of the differential amplifier; a second capacitive path between the second core output and the inputs of the differential amplifier; a chopping system having a high state and a low state, the chopping system coupling the first and second core outputs to the inputs of the differential amplifier, wherein when the chopping system is in the high state, a positive step voltage is applied to the common node of the capacitive core, and the chopping system couples the first core output to the inverting input of the differential amplifier and couples the second core output to the non-inverting input of the differential amplifier; and when the chopping system is in the low state, a negative step voltage is applied to the common node of the capacitive core, and the chopping system couples the first core output to the non-inverting input of the differential amplifier and couples the second core output to the inverting input of the differential amplifier.