Position sensing

A transducer for an inductive position sensor comprising a printed circuit board carrying a plurality of sensor coils including first and second coarse sensor coils for providing coarse position information, first and second fine sensor coils for providing fine position information and an excitation coil for energising a target;

• wherein the plurality of sensor coils are formed by conductor tracks on different layers of the printed circuit board that are connected together to define the plurality of sensor coils at a plurality of vias that connect together conductors on the different layers of the printed circuit board;
• wherein the printed circuit board comprises a through hole, a first plurality of vias arranged in first and second rings around the through hole and a second plurality of vias arranged in a third ring in proximity to an outer edge of the printed circuit board;
• wherein the fine sensor coils include radial conductor portions on a first layer of the printed circuit board that extend from vias in the first or second rings to vias in the third ring, wherein radial conductor portions of one of the fine sensor coils are connected to other radial conductor portions of the same one of the fine sensor coils on a second layer and wherein conductor coil portions of at least one coarse sensor coil or conductor coil portions of the excitation coil run in a space between the first and second rings of vias.

A transducer for an inductive position sensor, the transducer comprising a multi-layer printed circuit board, each layer comprising conductor portions that connect together through the layers at a plurality of vias to define a plurality of coil loop portions;

• wherein the printed circuit board includes a through hole and the plurality of coil loop portions include a first subset of coil loop portions, a second subset of coil loop portions and a third subset of coil loop portions;
• wherein loops defined by the first subset of coil loop portions and the second subset of coil loop portions do not enclose the through hole and are arranged peripherally around the through hole;
• wherein loops defined by the third subset of coil loop portions enclose the through hole;
• wherein the plurality of coil loop portions are connected together so that a current flow direction in the first subset of coil loop portions is opposite to a current flow direction in the second subset of coil loop portions and is the same as a current flow direction in the third subset of coil loop portions, whereby when current flows through the first, second and third subsets of coil loop portions, magnetic fields generated by the plurality of coil loop portions combine to reduce a net magnetic flux through said through hole.

Excitation circuitry for energising an excitation coil to excite a resonant target of an inductive position sensor, the excitation circuitry comprising:

• an impedance network that is coupled, in use, to the excitation coil and having a first state that presents a first impedance that is primarily capacitive to the excitation coil and a second state that presents a second impedance to the excitation coil, wherein a magnitude of the second impedance is at least twice that of the first impedance when measured at the target's resonant frequency;
• drive circuitry for driving the excitation coil via the impedance network with an excitation current to cause the excitation coil to generate an excitation magnetic field for energising the resonant target;
• and
• a controller for controlling the drive circuitry and the impedance network so that in a first time period, the impedance network is configured in said first state and the drive circuitry is configured to drive the excitation coil with said excitation current and so that in a second time period, the impedance network is configured in said second state and the drive circuitry is configured not to drive the excitation coil with said excitation current.