Displacement Converter
Electrostatic detection circuits utilize the varying distance or area between electrodes to resolve sub-micron movements of a proof mass. In a typical integration, the capacitive pickoff generates a change in electrical potential or current that tracks the physical state of the mechanical resonator. This component stops providing valid information when the gap between plates reaches a point where dielectric breakdown becomes possible.
Electronic Detection
Low-noise amplifiers convert the small signal shifts from the plates into measurable voltages. Because high impedance nodes are vulnerable to interference, the capacitive pickoff requires careful shielding within the sensor housing. Designers often apply a bias voltage to increase the sensitivity of the transimpedance stage.
Current injection from neighboring clocks can create a false image of movement in the final output stream.
Parasitic Capacitance
Unintended electrical paths through the substrate degrade the signal-to-noise ratio of the sensing element. Stray paths from bond pads or traces often exceed the variable signal from the capacitive pickoff during high frequency operation. Minimization occurs through guarded layouts and shortened routing paths.
Every millimetre of metal trace adds femtofarads of unwanted load that lowers the overall resolution.
Environmental Sensitivity
Humidity or trace contamination on the die surface creates leakage paths that interfere with the intended measurements. If the gap is exposed to air, the dielectric constant fluctuates with pressure and temperature. Hermetic packaging locks the behavior by maintaining a controlled environment around the capacitive pickoff elements.
Stability depends on the seal remaining intact over the entire life of the instrument.
