The U1a and U1b cross-coupled Schmidt trigger timers form a ~1 MHz RC multivibrator. The T_SENSE pulse width is inversely proportional to sensor displacement

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Other Materials from the Main Document

• Article «Capacitive position sensor with linearized output»
• Figure 1. The U1a and U1b cross-coupled Schmidt trigger timers form a ~1 MHz RC multivibrator. The T_SENSE pulse width is inversely proportional to sensor displacement
• Figure 2. Passive RC averaging of the T_SENSE output yields the analog position output
• Figure 3. This graph shows the sensor performance when OUT is connected to a 12 bit ADC using +5 V for its reference. The black curve (left axis) equals the plate separation (d) in millimeters. The red curve (right axis) equals the ADC lsb resolution in micrometers
• Figure 4. Averaging integrator A1 linearizes the displacement sensing response. R5 is shown as a precision type, albeit just out of force of habit. It, like the ON resistances of U2's switches, actually cancels out
• Figure 5. In this graph of the enhanced circuit results, the black curve equates to the sensor readout d in mm, with red at a constant 1 mV per micron resolution