Circuit for driving ultrasonic transducer

A driving circuit for generating a driving signal for an ultrasonic transducer including

• a frequency sweep means for effecting the frequency sweep over a predetermined frequency range;
• a means for operating the driving circuit under a sweep control mode in which the frequency of the driving signal is increased or decreased continuously within said predetermined frequency range with the aid of said frequency sweep means;
• a means for operating the driving circuit under a feedback control mode in which the frequency of the driving signal is controlled to follow a varying resonance frequency of the ultrasonic transducer;
• and
• a switching means for selectively driving said driving circuit between said sweep control mode and the feedback control mode by comparing the phases of the voltage and current of the driving signal, the improvement being characterized in that said switching means comprises an impedance detector for detecting an impedance of the ultrasonic transducer, a comparator for comparing the impedance of the ultrasonic transducer with a predetermined threshold value and generating a resonance point detection signal when the impedance is decreased below said threshold value, and a switching circuit for changing the sweep control mode into the feedback control mode in response to said resonance point detection signal.

A driving circuit for generating a driving signal for an ultrasonic transducer comprising

• a phase lock loop for adjusting a frequency of the driving signal to follow a resonance frequency of the ultrasonic transducer in accordance with a voltage phase detection signal representing a phase of a voltage of the driving signal and a current phase detection signal;
• a reference signal generating circuit for generating a reference signal having a frequency which is varied continuously;
• and
• a control means for selectively driving said phase lock loop between a first control mode in which during a start period, the frequency of the driving signal is controlled in accordance with a phase difference between the reference signal and the voltage phase detection signal until the driving signal is phase-locked with a resonance frequency of the ultrasonic transducer, and a second control mode in which after the driving signal has been phase-locked with the resonance frequency of the ultrasonic transducer, the frequency of the driving signal is controlled in accordance with a phase difference between the voltage phase detection signal and the current phase detection signal.

A driving circuit for driving an ultrasonic transducer comprising

• a frequency sweep means for effecting the frequency sweep over a predetermined frequency range;
• a means for operating the driving circuit under a sweep control mode in which the frequency of the driving signal is increased or decreased continuously within said predetermined frequency range with the aid of said frequency sweep means;
• a means for operating the driving circuit under a feedback control mode in which the frequency of the driving signal is controlled to follow a varying resonance frequency of the ultrasonic transducer;
• a switching means for selectively driving said driving circuit between said sweep control mode and the feedback control mode;
• a means for amplifying the driving signal with a variable amplification factor;
• and
• an amplification control means for controlling the amplification factor of said amplifying means such that the amplification factor is gradually increased from a lower value during the sweep control mode to a higher value during the feedback control mode.