Hall-effect based linear motor controller
A linear motion control device for use in a linear control system is presented. The linear motion control device includes a coil driver to drive a coil that, when driven, effects a linear movement by a motion device having a magnet. The linear motion control device also includes a magnetic field sensor to detect a magnetic field associated with the linear movement and an interface to connect an output of the magnetic field sensor and an input of the coil driver to an external controller. The interface includes a feedback loop to relate the magnetic field sensor output signal to the coil driver input.
1. A device comprising:
a coil driver to drive a coil that,-hen driven, effects a linear displacement of a motion device having a magnet;
a magnetic field sensor to detect a magnetic field associated with the linear displacement and to produce an output signal in response thereto; and
an interface, responsive to requests provided by an external controller and corresponding to desired linear displacements of the motion device, to receive a request as a first input and the magnetic field sensor output signal as a second input, and to produce an input signal to the coil driver having a level indicative of a relationship of the second input with respect to the first input
wherein the interface comprises a first difference amplifier comprising a first port configured to receive the first input, a second port configured to receive the second input and a third port to provide an output of the first difference amplifier,
wherein the interface further comprises a second difference amplifier comprising a first port configured to receive the output of the first difference amplifier and a second port configured to provide the input signal to the coil driver, and
wherein the second difference amplifier further comprises a third port coupled to the coil driver and coupled to ground through a sense resistor.
2. The device of claim 1 wherein the interface includes a difference amplifier to receive as inputs the first input and the second input, and to produce an output signal therefrom.
3. The device of claim 2 wherein the output signal produced by the difference amplifier is the input signal to the coil driver.
4. The device of claim 1 wherein the magnetic field sensor comprises a Hall sensor.
5. The device of claim 1 wherein the magnetic field sensor comprises a type of magneto-resistive sensor.
6. The device of claim 1 wherein the coil driver is configured to connect to the coil to drive current through the coil in one direction.
7. The device of claim 6 wherein the coil driver comprises a voice coil driver.
8. The device of claim 1 wherein the coil driver is configured to connect to the coil to drive current through the coil in more than one direction.
9. The device of claim 8 wherein the coil driver comprises a linear motor driver that includes an H-bridge circuit.
10. The device of claim 1 wherein the coil driver, the magnetic field sensor and the interface are integrated as a semiconductor integrated circuit.
11. A system comprising:
a controller; and
a linear motion control device, coupled to the controller, comprising:
a coil driver to drive a coil that, when driven, effects a linear displacement of a motion device having a magnet;
a magnetic field sensor to detect a magnetic field associated with the linear displacement and to produce an output signal in response thereto; and
an interface, responsive to requests provided by the controller and corresponding to desired linear displacements of the motion device, to receive a request as a first input and the magnetic field sensor output signal as a second input, and to produce an input signal to the coil driver having a level indicative of a relationship of the second input with respect to the first input
wherein the interface comprises a first difference amplifier comprising a first port configured to receive the first input, a second port configured to receive the second input and a third port to provide an output of the first difference amplifier,
wherein the interface further comprises a second difference amplifier comprising a first port configured to receive the output of the first difference amplifier and a second port configured to provide the input signal to the coil driver, and
wherein the second difference amplifier further comprises a third port coupled to the coil driver and coupled to ground through a sense resistor.
12. The system of claim 11 wherein the controller is configured to use the linear motion control device to focus the lens of a camera.
13. The system of claim 11 wherein the coil driver, the magnetic field sensor and the interface are integrated as a semiconductor integrated circuit.
14. The system of claim 13 wherein the semiconductor integrated circuit and the controller reside on a camera lens focusing module.
15. The system of claim 11 wherein the magnetic field sensor is a Hall sensor and the coil driver is a voice coil driver.
16. The device of claim 1 wherein the interface comprises circuitry to return a signal based on the magnetic field sensor output signal to the external controller.
17. The device of claim 1 wherein, when the motion device is a lens of a camera, each request comprises a value for a desired travel of the lens.
18. The device of claim 1 wherein the coil driver input signal is operable to cause the coil driver to drive the coil until the linear displacement of the motion device results in the coil driver input signal level indicating that the relationship of the second input with respect to the first input is a predetermined relationship.
19. The device of claim 18 wherein the predetermined relationship comprises the second input matching the first input.