Circuit for automatically driving mechanical device at its resonance frequency

• US 6,339,368 B1
• Filed: 03/31/2000
• Issued: 01/15/2002
• Est. Priority Date: 03/31/2000
• Status: Expired due to Term

• Current Assignee: IXYS Intl Limited (Littelfuse Incorporated)
• Original Assignee: ZiLOG Incorporated (Littelfuse Incorporated)
• Inventors: Leith, James W.
• Primary Examiner(s): Wu, Daniel J.
• Assistant Examiner(s): Nguyen, Phung T
• Application Number:
  US09/539,764
• Time in Patent Office: 655 Days
• Field of Search: 340/384.4, 340/384.6, 340/384.73, 340/384.1, 381/97, 381/114, 381/150, 331/4
• US Class Current: 340/384.4
• CPC Class Codes: B06B 1/0253 taken directly from the generator circuit
• CPC Class Codes: G08B 3/10 using electric transmission; using electromagnetic transmission

Abstract

A circuit for automatically driving a mechanical device at its resonance frequency is provided. To do so, the circuit detects non-resonance driving conditions of the mechanical device being coupled to and driven by such circuit. Based on such detection, the circuit generates a signal to drive the device at its resonance frequency.

Claims

1. An acoustic transducer system comprising:

a power supply;

an acoustic transducer having a first electrical terminal coupled to the power supply and a second electrical terminal coupled to a reference ground; and

a phase-locked loop circuit detecting a phase difference between first and second signals at the first and second electrical terminals, respectively, and generating an output signal based on the detected phase difference to drive the acoustic transducer via a feedback connection forming a closed loop from the phase-locked loop circuit back to the second electrical terminal, wherein the output signal drives the acoustic transducer at its resonance frequency when the detected phase difference is negligible.

2. The acoustic transducer system of claim 1 further comprises:

a first zero-crossing limiter, coupled to and between the first electrical terminal and the phase-locked loop circuit, converting the first signal to a third signal; and

a second zero-crossing limiter, coupled to and between the second electrical terminal and the phase-locked loop circuit, converting the second signal to a fourth signal, wherein the third and fourth signals have a common zero-crossing reference, and further wherein the phase-locked loop circuit detects a phase difference between the third and fourth signals.

3. The acoustic transducer system of claim 2 further comprises:

a first comparator, coupled to and between the first zero-crossing limiter and the phase-locked loop circuit, converting the third signal to a first digital signal; and

a second comparator, coupled to and between the second zero-crossing limiter and the phase-locked loop circuit, converting the fourth signal to a second digital signal, wherein the phase-locked loop circuit detects a phase difference between the first and second digital signals.

4. The acoustic transducer system of claim 2 further comprises a comparator, coupled to and between the second zero-crossing limiter and the phase-locked loop circuit, converting the fourth signal to a digital signal, wherein phase-locked loop circuit detects a phase difference between the third signal and the digital signal.

5. The acoustic transducer system of claim 2, wherein each of the first and second zero-crossing limiter comprises:

an amplifier having an inverting terminal, a non-inverting terminal and an output terminal, said non-inverting terminal coupled to a reference voltage and said output terminal coupled to the phase-locked loop circuit;

a capacitive element coupled to one of the first or second electrical terminal of the acoustic transducer;

a first resistive element coupled to the capacitive element and the inverting terminal;

a second resistive element coupled to the inverting terminal and the output terminal;

a first diode having an anode that is coupled to the output terminal and a cathode that is coupled to the inverting terminal; and

a second diode having an anode that is coupled to the inverting terminal and a cathode that is coupled to the output terminal.

6. The acoustic transducer system of claim 5, wherein maximum values of the third and fourth signals are substantially identical, and further wherein minimum values of the third and fourth signals are substantially identical.

7. The acoustic transducer system of claim 1, wherein the phase-locked loop circuit comprises:

a phase detector detecting the phase difference;

a low pass filter converting the detected phase difference to a voltage level; and

a voltage controlled oscillator generating the output signal in response to the voltage level from the lowpass filter.

8. The acoustic transducer system of claim 1, wherein the output signal has a frequency that is higher than frequencies of the first and second signals when the first signal leads the second signal, and further wherein the output signal has a frequency that is lower than frequencies of the first and second signals when the first signal lags the second signal.

9. The acoustic transducer system of claim 1, wherein the acoustic transducer is a piezoelectric transducer.

10. The acoustic transducer system of claim 1 further comprises a switching device driving the acoustic transducer in response to the output signal, wherein the switching device is coupled to and between the second electrical terminal and the reference ground, and further wherein the acoustic transducer is an electro-mechanical transducer or a loudspeaker.

11. The acoustic transducer system of claim 10, wherein the switching device is a metal-oxide semiconductor field-effect transistor.

12. The acoustic transducer system of claim 10 further comprises a resistive element coupled to and between the phase-locked loop circuit and the switching device, wherein the switching device is a bipolar junction transistor.

13. The acoustic transducer system of claim 10 further comprises a resistive element coupled to and between the switching device and the reference round.

14. The acoustic transducer system of claim 1 further comprises a lock detect circuit detecting a phase difference between either the first or second signal and the output signal of the phase locked loop circuit and providing an indication that the acoustic transducer is being driven at its resonance frequency when the detected phase difference is negligible.

15. The acoustic transducer system of claim 5, wherein the amplifier is an operational amplifier.

16. A circuit automatically driving an acoustic transducer coupled to the circuit at a resonance frequency when a power supply is provided to drive the acoustic transducer, comprising:

a phase detector continuously detecting a phase difference between first and second signals at first and second electrical terminals of the acoustic transducer, respectively;

a lowpass filter converting the detected phase difference to a voltage level; and

a voltage controlled oscillator generating an output signal in response to the voltage level from the lowpass filter, said output signal driving the acoustic transducer at a resonance frequency when the detected phase difference is negligible,

wherein the output signal drives the acoustic transducer via a feedback connection forming a closed loop from the voltage controlled oscillator back to the second electrical terminal, and

further wherein the first electrical terminal is coupled to the power supply and the second electrical terminal is coupled to a reference ground.

23. The circuit of claim 16, wherein the acoustic transducer is a piezoelectric transducer.

24. The circuit of claim 16 further comprises a switching device driving the acoustic transducer in response to the output signal, wherein the switching device is coupled to and between the second electrical terminal and the reference ground, and further wherein the acoustic transducer is an electro-mechanical transducer or a loudspeaker.

25. The circuit of claim 24, wherein the switching device is a metal-oxide semiconductor field-effect transistor.

26. The circuit of claim 24 further comprises a resistive element coupled to and between the phase-locked loop circuit and the switching device, wherein the switching device is a bipolar junction transistor.

27. The circuit of claim 24 further comprises a resistive element coupled to and between the switching device and the reference ground.

17. A circuit automatically driving an acoustic transducer coupled to the circuit at a resonance frequency when a power supply is provided to drive the acoustic transducer, comprising:

a phase detector continuously detecting a phase difference between first and second signals at first and second electrical terminals of the acoustic transducer, respectively;

a lowpass filter converting the detected phase difference to a voltage level;

a voltage controlled oscillator generating an output signal in response to the voltage level from the lowpass filter, said output signal driving the acoustic transducer at a resonance frequency when the detected phase difference is negligible;

a first zero-crossing limiter, coupled to and between the first electrical terminal and the phase detector, converting the first signal to a third signal; and

a second zero-crossing limiter, coupled to and between the second electrical terminal and the phase detector, converting the second signal to a fourth signal, wherein the third and fourth signals have a common zero-crossing reference, and further wherein the phase detector detects a phase difference between the third and fourth signals.

18. The circuit of claim 17 further comprises:

a first comparator, coupled to and between the first zero-crossing limiter and the phase detector, converting the third signal to a first digital signal; and

a second comparator, coupled to and between the second zero-crossing limiter and the phase detector, converting the fourth signal to a second digital signal, wherein the phase detector detects a phase difference between the first and second digital signals.

19. The circuit of claim 17 further comprises a comparator, coupled to and between the second zero-crossing limiter and the phase detector, converting the fourth signal to a digital signal, wherein the phase detector detects a phase difference between the third signal and the digital signal.

20. The circuit of claim 17, wherein each of the first and second zero-crossing limiter comprises:

an amplifier having an inverting terminal, a non-inverting terminal and an output terminal, said non-inverting terminal coupled to a reference voltage and output terminal coupled to the phase detector;

a capacitive element coupled to one of the first or second electrical terminal of the acoustic transducer;

a first resistive element coupled to the capacitive element and the inverting terminal;

a second resistive element coupled to the inverting terminal and the output terminal;

a first diode having an anode that is coupled to the output terminal and a cathode that is coupled to inverting terminal; and

a second diode having an anode that is coupled to the inverting terminal and a cathode that is coupled to the output terminal.

21. The circuit of claim 20, wherein maximum values of the third and fourth signals are substantially identical, and further wherein minimum values of the third and fourth signals are substantially identical.

29. The circuit of claim 20, wherein the amplifier is an operational amplifier.

22. A circuit automatically driving an acoustic transducer coupled to the circuit at a resonance frequency when a power supply is provided to drive the acoustic transducer, comprising:

a phase detector continuously detecting a phase difference between first and second signals at first and second electrical terminals of the acoustic transducer, respectively;

a lowpass filter converting the detected phase difference to a voltage level; and

a voltage controlled oscillator generating an output signal in response to the voltage level from the lowpass filter, said output signal driving the acoustic transducer at a resonance frequency when the detected phase difference is negligible,

wherein the output signal has a frequency that is higher than frequencies of the first and second signals when the first signal leads the second signal, and further wherein the output signal has a frequency that is higher than frequencies of the first and second signals when the first signal lags the second signal.

28. A circuit automatically driving an acoustic transducer coupled to the circuit at a resonance frequency when a power supply is provided to drive the acoustic transducer, comprising:

a phase detector continuously detecting a phase difference between first and second signals at first and second electrical terminals of the acoustic transducer, respectively;

a lowpass filter converting the detected phase difference to a voltage level;

a voltage controlled oscillator generating an output signal in response to the voltage level from the lowpass filter, said output signal driving the acoustic transducer at a resonance frequency when the detected phase difference is negligible; and

a lock detect circuit detecting a phase difference between either the first or second signal and the output signal of the voltage controller oscillator and providing an indication that the acoustic transducer is being driven at its resonance frequency when the detected phase difference is negligible.