Circuitry for estimating displacement of a piezoelectric transducer

1. Circuitry for estimating a displacement of a piezoelectric transducer in response to a drive signal applied to the piezoelectric transducer, the circuitry comprising:

monitoring circuitry configured to be coupled to the piezoelectric transducer and to output a sense signal indicative of an electrical signal associated with the piezoelectric transducer as a result of the drive signal;

wherein the circuitry is configured to generate a difference signal based on the drive signal and the sense signal;

and wherein the circuitry further comprises processing circuitry configured to apply at least one transfer function to the difference signal to generate a signal indicative of the displacement of the piezoelectric transducer.

2. Circuitry according to claim 1 , wherein the drive signal comprises a voltage and the sense signal is indicative of a current through the piezoelectric transducer as a result of the drive signal, or wherein the drive signal comprises a current and the sense signal is indicative of a voltage across the piezoelectric transducer as a result of the drive signal.

3. Circuitry according to claim 1 , wherein the at least one transfer function comprises a transfer function corresponding to a second order low pass filter.

4. Circuitry according to claim 3 , wherein the at least one transfer function comprises a transfer function of the form:

T

=

1

+

ω

0

(

1

Q

+

ω

0

)

s

2

+

ω

0

Q

⁢

s

+

ω

0

2

⁢

G

where G is a gain.

5. Circuitry according to claim 3 , wherein the at least one transfer function further comprises a transfer function corresponding to a first order high-pass filter and/or one or more transfer functions corresponding to a second order band-pass filter.

6. Circuitry according to claim 1 , wherein the at least one transfer function comprises a transfer function corresponding to a first first order low-pass filter, a transfer function corresponding to a second first order low-pass filter, and/or one or more transfer functions corresponding to a second order band-pass filter.

7. Circuitry according to claim 1 , wherein the sense circuitry comprises a sense impedance.

8. Circuitry according to claim 7 , wherein the sense impedance comprises one or more of: a capacitor, a resistor and an inductor.

9. Circuitry according to claim 1 , wherein the circuitry further comprises system identification circuitry configured to determine the transfer function.

10. Circuitry according to claim 9 , wherein the system identification circuitry is configured to determine an impedance of the piezoelectric transducer based on the sense signal and the drive signal.

11. Circuitry according to claim 10 , wherein the system identification circuitry is configured to determine the transfer function based on the determined impedance of the piezoelectric transducer.

12. Circuitry according to claim 10 , wherein the system identification circuitry is configured to identify one or more resonance frequencies of the piezoelectric transducer based on the determined impedance.

13. Circuitry according to claim 12 , wherein the system identification circuitry is configured to identify a first resonance frequency of the piezoelectric transducer, and to determine a first transfer function based on a frequency and a Q factor associated with the identified first resonance frequency.

14. Circuitry according to claim 13 , wherein the system identification circuitry is configured to identify one or more further resonance frequencies of the piezoelectric transducer, and to determine one or more corresponding further transfer functions, each based on a frequency and a Q factor associated with a respective one of the one or more identified further resonance frequencies.

15. An integrated circuit comprising the circuitry of claim 1 .

16. A system comprising the circuitry of claim 1 and a piezoelectric transducer.

17. Circuitry for controlling a displacement of a piezoelectric transducer, the circuitry comprising:

transducer driver circuitry for outputting a drive signal to the piezoelectric transducer;

monitoring circuitry configured to be coupled to the piezoelectric transducer and to output a sense signal indicative of an electrical signal associated with the piezoelectric transducer as a result of the drive signal;

wherein the circuitry is configured to generate a difference signal based on the drive signal and the sense signal;

wherein the circuitry further comprises processing circuitry configured to apply a transfer function to the difference signal to generate a signal indicative of a displacement of the piezoelectric transducer,

and wherein the drive signal is based on an error signal between an input signal to the circuitry, the input signal representative of a desired displacement of the piezoelectric transducer, and the signal indicative of the displacement.

18. An integrated circuit comprising the circuitry of claim 17 .

19. A system comprising the circuitry of claim 17 and a piezoelectric transducer.

20. Circuitry for controlling a sound pressure level at a piezoelectric transducer, the circuitry comprising:

transducer driver circuitry for outputting a drive signal to the piezoelectric transducer;

monitoring circuitry configured to be coupled to the piezoelectric transducer and to output a sense signal indicative of an electrical signal associated with the piezoelectric transducer as a result of the drive signal;

wherein the circuitry is configured to generate a difference signal based on the drive signal and the sense signal;

wherein the circuitry further comprises processing circuitry configured to apply a transfer function to the difference signal to generate a signal indicative of a sound pressure level at the piezoelectric transducer,

and wherein the drive signal is based on an error signal between an input signal to the circuitry, the input signal indicative of a desired sound pressure level at the piezoelectric transducer, and the signal indicative of an actual sound pressure level.