Engineering Parameters:
Coarse Gain, Fine Gain, and Offset Subtraction

The coarse gain ratio, fine gain ratio, and offset subtraction are engineering controls for advanced users during the development process. These parameters exist to provide visibility into the behaviour of the runtime calibration algorithm.

The primary controls for adjusting sensitivity and resolution are the Conversion_Count and Conversion_Gain parameters. At runtime, these two parameters are inputs to the calibration algorithm, which adjusts the peripheral control knobs: coarse gain, fine gain, and offset subtraction- to achieve the requested performance for each element in each sensor. The configuration for each element is stored in a structure that get associated with each element. It is important to note that these values are recalculated after every device reset, and may differ depending on where a system is used. If the runtime re-calibration feature is enabled, any time an element's LTA drifts out of range due to environmental drift the sensor will be re-calibrated to regain the desired sensitivity. These parameters are provided for development. Note that any values set here will not persist after the target device is reset or the sensor is recalibrated.

Coarse Gain Ratio
The coarse gain ratio applies a coarse scaling factor to the relationship between the external capacitor being measured and the internal sample capacitor.

Fine Gain Ratio
The fine gain ratio applies a fine scaling factor to the relationship between the external capacitor being measured and the internal sample capacitor.

Offset Subtraction
The offset subtraction applies a capacitive DC offset, reducing the component of the measurement that is associated with parasitic capacitance.

Affected Software Parameters
The Coarse_Gain_Ratio parameter corresponds to the ui8CoarseGainRatio member of the tCaptivateElementTuning type in the CapTIvate Touch Library.
The Fine_Gain_Ratio parameter corresponds to the ui8FineGainRatio member of the tCaptivateElementTuning type in the CapTIvate Touch Library.
The Offset_Subtraction parameter corresponds to the ui16OffsetTap member of the tCaptivateElementTuning type in the CapTIvate Touch Library.