Publication

Abstract : This paper presents an efficient Inductance-to-Time Converter (LTC) that provides a quasi-digital output whose pulse-on time is proportional to the inductance of a single-element type sensor. The LTC operates with a negative feedback mechanism, which ensures that the final output is independent of the linearity error present in the forward path elements of the converter. The proposed relaxation oscillator-based operation can enhance the update rate of the inductance measurement. In addition, the inductance measured using the converter is made insensitive to the series coil-resistance of the sensor. A prototype of the LTC with an update rate of 10 kHz was developed in the laboratory, with an excellent linearity performance along with a reduced settling time. It was observed that the design produced a worst-case linearity error of 0.29% and a settling time of 12.4 ms when the inductance was varied from 0 to 20 mH. Furthermore, the prototype showed negligible sensitivity towards the coil resistance of the sensor, with a worst-case error of 0.65%, when the series resistance was varied from 40 Ω to 1040 Ω. The test results indicate superior performance of the developed prototype over existing architectures.