Calibration method, corresponding circuit and apparatus

A circuit configured to be coupled to a piezoelectric transducer and to a notch filter coupled to an output of the piezoelectric transducer, wherein the piezoelectric transducer configured to transduce mechanical vibrations into transduced electrical signals at a pair of sensor electrodes, the piezoelectric transducer has a resonance frequency, the notch filter configured to receive the transduced electrical signals and produce filtered signals from the transduced electrical signals, the circuit comprising calibration circuitry configured to:

• stimulate resonant oscillation of the piezoelectric transducer by applying at least one pulse electrical stimulation signal to the pair of sensor electrodes;
• detect, at the pair of sensor electrodes, at least one electrical signal resulting from the stimulated resonant oscillation, wherein the at least one electrical signal resulting from the stimulated resonant oscillation oscillates at the resonance frequency of the piezoelectric transducer;
• measure a frequency of oscillation of the at least one electrical signal resulting from the stimulated resonant oscillation using a measuring circuit to obtain a measured resonance frequency of the piezoelectric transducer;
• and
• tune a stopband frequency of notch filter coupled to the piezoelectric transducer to match the measured resonance frequency of the piezoelectric transducer, wherein tuning the stopband frequency comprises measuring the stopband frequency of the notch filter using the same measuring circuit used to measure the frequency of oscillation of the at least one electrical signal.

A integrated circuit comprising:

• an input interface configured to be coupled to a piezoelectric transducer;
• an amplifier having an input coupled to the input interface;
• a notch filter coupled to an output of the amplifier;
• an activatable feedback path coupled between an output of the notch filter and the input of the amplifier;
• a frequency measurement circuit coupled to the output of the amplifier;
• and
• a calibration circuit configured to:
• deactivate the feedback path and obtain a frequency measurement of a resonant frequency of the piezoelectric transducer from the frequency measurement circuit while the first feedback path is deactivated,
• activate the feedback path and obtain a frequency measurement of a stopband frequency of the notch filter from the frequency measurement circuit while the first feedback path is activated, and
• adjust the stopband frequency of the notch filter to correspond to the resonant frequency of the piezoelectric transducer based on the frequency measurement of the stopband frequency of the notch filter and the frequency measurement of the resonant frequency of the piezoelectric transducer.