Fast Automatic Tuning of a Synthetic Inductor for Automotive Transformer-Less Ultrasonic Sensor in Park Assist Systems

This paper presents a novel shunt tuning method suitable for transformer-less ultrasonic sensors in park assist systems. The method enables tuning of an inductive part of LR shunt that is used for a transducer damping. The method relies on the knowledge of a transducer own serial resonance frequency and the measurement of a parallel resonance frequency, which corresponds to the transducer parasitic capacity and shunt inductance. From the ratio of these two resonance frequencies, the method predicts how the inductance must be tuned to achieve optimal damping performance. To enable measurement of the parallel resonance frequency inductance scaling by a factor of four is employed. The scaled inductance shifts the parallel resonance frequency away from the serial resonance frequency and thus distinguishes them. This paper is supported by practical experiments using a fabricated test chip with a tunable synthetic inductor that confirms its performance and shows improvements compared to previous solutions without adaptive tuning mechanisms.