Near zero power fully integrated digital conversion, sensors and sensing methods

A charging to digital converter sensor in a CMOS integrated circuit, the sensor comprising:

• a voltage or current reference generator that generates a first reference voltage or current that is constant with respect to a sensed property;
• a voltage or current reference generator that generates a second reference voltage or current that varies with respect to the sensed property;
• two paths including on-chip capacitors charged with a sub nanowatt current reference such that a first ramp voltage or current is generated in one of the two paths and a second ramp voltage or current is generated in a second of the two paths, wherein the first ramp voltage or current is compared to the first reference voltage or current and the second ramp voltage or current is compared to the second reference voltage or current;
• a digitizer for digitizing the sensed property by comparing charging time between the two paths and adjusting the charging rate of one of the two paths by increasing or decreasing the amount of capacitance in that path, until both of the two paths have the same charging time to reach the first and second reference voltages or currents, respectively, wherein a digital output represents a value of the capacitance;
• and
• digital feedback to reset the converter to restart the charging time.