The LDC1312/LDC1314 can automatically determine the appropriate sensor current drive when entering Active Mode. For the majority of applications, it is recommended to program a fixed current drive for consistent measurement performance. The automatic sensor amplitude setting is useful for initial system prototyping if the sensor amplitude is unknown. When this function is enabled, the LDC attempts to find the IDRIVEx setting which results in a sensor amplitude between 1.2 VP and 1.8VP. For systems which have a large variation in target interaction, the LDC1312/LDC1314 may select a current drive setting which has poorer repeatability over the range of target interactions. In addition, measurement repeatability will be poorer with different sensor current drives. To enable the automatic sensor amplitude, set RP_OVERRIDE to b0.
The following sequence uses auto-calibration to configure sensor drive current for a sensor with an unknown RP:
If the current drive results in the oscillation amplitude greater than 1.8 V, the internal ESD clamping circuit will become active. This may cause the sensor frequency to shift so that the output values no longer represent a valid system state. If the current drive is set at a lower value, the SNR performance of the system will decrease, and at near zero target range, oscillations may completely stop, and the output sample values will be all zeroes.
If there are significant differences in the sensor construction for different channels, then this process should be repeated for each channel.