US Patent 9122330 Controlling a user's tactile perception in a dynamic physical environment

To maintain consistency in different environments with different impedances, a high voltage current driver may be used as a signal generator to output a tactile signal with a constant current. The constant current ensures that the voltage between the user's finger and the object's surface or electrode remains the same even if impedances in the electrical path change. Specifically, the current driver includes a current sensing circuit that determines the average current being generated. Using a feedback loop, the measured current is compared to a reference current to determine if the correct tactile sensation is perceived by the user. As the impedance changes, the current driver detects the resulting change in the signal's current and adjusts the voltage amplitude of the generated tactile signal in order to match the measured current to the reference current.