Transducer controller and method therefor
In an embodiment, a transducer controller is configured to apply a damping signal to reduce energy stored in the transducer after the transducer has been driven with a drive signal to form a transmitted acoustic signal.
1. A controller for an acoustic transducer comprising:
the controller configured to form a drive signal to drive the acoustic transducer during a drive phase; and
a damping circuit configured to form a fixed charge and to apply the fixed charge to the acoustic transducer in response to a substantially zero crossing of a circulating current within the acoustic transducer, the damping circuit configured to form a variable charge and to apply the variable charge to the acoustic transducer in response to a positive to negative transition of the circulating current.
2. The controller of claim 1 wherein the damping circuit includes a plurality of switches configured to charge a first capacitor to a first voltage to form the fixed charge, and to cyclically apply the first capacitor to the acoustic transducer in response to the substantially zero crossing of the circulating current without recharging the first capacitor between applications to the acoustic transducer.
3. The controller of claim 1 wherein the damping circuit is configured to form a closed-loop current that is representative of the circulating current and to charge a closed-loop capacitor with the closed-loop current to form the variable charge.
4. A controller for an acoustic transducer comprising:
the controller configured to form a drive signal to drive the acoustic transducer during a drive phase; and
a damping circuit configured to form a fixed charge and to apply the fixed charge to the acoustic transducer in response to a substantially zero crossing of a circulating current within the acoustic transducer, the damping circuit configured to form a variable charge and to apply the variable charge to the acoustic transducer in response to a positive to negative transition of the circulating current wherein the damping circuit includes a current comparator configured to receive a first input signal that is representative of the circulating current and to determine if the circulating current has a positive value or a negative value and to determine if a value of the circulating current is greater than a threshold value.
5. The controller of claim 4 wherein the current comparator includes a first switch coupled to a closed-loop capacitor and configured to be enabled to couple the closed-loop capacitor to the acoustic transducer wherein the first switch is enabled in response to detecting the positive to negative transition of the circulating current.
6. The controller of claim 4 wherein the current comparator includes a buffer that receives the first input signal and forms a first current that is representative of the first input signal.
7. A controller for an acoustic transducer comprising:
the controller configured to form a drive signal to drive the acoustic transducer during a drive phase; and
a damping circuit configured to form a fixed charge and to apply the fixed charge to the acoustic transducer in response to a substantially zero crossing of a circulating current within the acoustic transducer, the damping circuit configured to form a variable charge and to apply the variable charge to the acoustic transducer in response to a positive to negative transition of the circulating current, the damping circuit including a switch coupled in parallel with a closed-loop capacitor.
8. The controller of claim 1 wherein the controller forms the variable charge to be representative of stored energy remaining in the acoustic transducer.
9. The controller of claim 1 wherein the controller is configured to apply the fixed charge prior to applying the variable charge.
10. The controller of claim 1 wherein the controller also includes a driver circuit to form the drive signal.
11. The controller of claim 10 wherein the damping circuit assists in forming the drive signal.
12. The controller of claim 1 wherein the damping circuit measures a frequency of the circulating current.
13. The controller of claim 12 wherein the damping circuit changes a frequency of applying either the fixed charge or the variable charge in response to a change in the frequency of the circulating current.
14. The controller of claim 4 wherein the controller includes a sensor circuit for forming the first input signal that is representative of the circulating current.
15. The controller of claim 4 wherein the damping circuit includes a resistor coupled to receive the signal that is representative of the circulating current and forms a voltage that is representative of the circulating current.
16. The controller of claim 15 wherein the damping circuit includes an integrator coupled to integrate the voltage.
17. The controller of claim 4 wherein the damping circuit includes a zero crossing detector configured to detect the zero crossing of the circulating current.
18. The controller of claim 4 wherein the damping circuit includes a damping driver that forms a damping signal to drive the acoustic transducer with the fixed charge of the variable charge.
19. The controller of claim 18 wherein the damping drive assists in forming the drive signal.
20. A controller for an acoustic transducer comprising:
the controller configured to form a drive signal to drive the acoustic transducer during a drive phase; and
a damping circuit configured to form a fixed charge and to apply the fixed charge to the acoustic transducer in response to a substantially zero crossing of a circulating current within the acoustic transducer wherein the damping circuit detects each zero crossing of the circulating current, the damping circuit configured to form a variable charge and to apply the variable charge to the acoustic transducer in response to a positive to negative transition of the circulating current.