Embodiments of the present invention are related to position sensors and, in particular, to optimization of vias in a long-coil position sensor.
Position sensors are used in various settings for measuring the position of one component with respect to another. Inductive position sensors can be used in automotive, industrial and consumer applications for absolute rotary and linear motion sensing. In many inductive positioning sensing systems, a transmit coil is used to induce eddy currents in a metallic target that is sliding or rotating above a set of receiver coils. Receiver coils receive the magnetic field generated from eddy currents and the transmit coils and provide signals to a processor. The processor uses the signals from the receiver coils to determine the position of the metallic target above the set of coils. The processor, transmitter, and receiver coils may all be formed on a printed circuit board (PCB).
Long position sensors, which are typically position sensors that span 10 cms or more in length, have a lot of uses, especially in cars, tractors, trucks, and other such functions. A long position sensor can replace more expensive sensors that may require a relatively large number of individual switches. The long position sensor can be controlled by a single integrated circuit chip and therefore occupies a relatively smaller space than alternatives. However, long position sensors suffer from larger non-linearity problems, which are harder to overcome.
Therefore, there is a need to develop better, more accurate inductive position sensing technologies.
A position sensor is presented. Embodiments of a position sensor according to some embodiments includes a printed circuit board and one or more receive coils formed on the printed circuit board, each of the one or more receive coils including first traces formed on a top surface of the printed circuit board, second traces formed on a bottom surface of the printed circuit board, and vias formed through the printed circuit board to connect the first traces with the second traces, wherein a correction area is formed with the first traces or the second traces that correct signals from the one or more receive coils resulting from signals from a bad area formed by the vias. long position sensor is presented.
A method of forming a position sensor according to some embodiments includes determining first traces of one or more receive sensors to be formed on a top surface of a printed circuit board; determining second traces of the one or more receive sensors to be formed on a bottom surface of a printed circuit board; determining vias that connect the first traces with the second traces; determining a bad area formed by connecting the first traces with the bottom traces with the vias; and determining a correction area to be formed in one of the first traces or the second traces based on the bad area and a magnetic field generated by a transmit coil, the correction area adjusting for effects from the bad area.
These and other embodiments are discussed below with respect to the following figures.
These and other aspects of embodiments of the present invention are further discussed below.
In the following description, specific details are set forth describing some embodiments of the present invention. It will be apparent, however, to one skilled in the art that some embodiments may be practiced without some or all of these specific details. The specific embodiments disclosed herein are meant to be illustrative but not limiting. One skilled in the art may realize other elements that, although not specifically described here, are within the scope and the spirit of this disclosure.
This description illustrates inventive aspects and embodiments should not be taken as limiting—the claims define the protected invention. Various changes may be made without departing from the spirit and scope of this description and the claims. In some instances, well-known structures and techniques have not been shown or described in detail in order not to obscure the invention.
Embodiments of the present provide optimization structures to correct for non-linearities in the via structures of a long position sensor. These optimization structures can take the form of additional an additional area on a bottom of the printed circuit board (PCB) that can compensate for the adverse effects of the distortion cause by the vertical vias.
With regard to this application, sensor structures are formed on a top and a bottom of a printed circuit board (PCB) and coupled by conductive traces in vias through the PCB. Sensors are formed relative to a plane of the PCB, which is referred to as the plane of the PCB or the horizontal plane. Vias are then formed vertically through the PCB. All directions are referenced to the plane of the PCB with regard to the terms horizontal, vertical, top, and bottom regardless of the orientation of the PCB with respect to any other reference system.
During operation, transmitter coil 102 is driven to generate an electromagnetic field. Ideally in the absence of a conductive target (not shown), sine coil 104 and cosine coil 106 are formed with current loops where the induced magnetic field directly from transmitter coil 102 is canceled and results in no signal from sine coil 104 and cosine coil 106. In the presence of a target positioned over sine coil 104 and cosine coil 106, the electromagnetic field generated by transmitter coil 102 induces eddy currents in the target. The eddy currents in the target generate magnetic fields that in turn generate currents in sine coil 104 and cosine coil 106 that varies with the position of target over position sensor 100.
However, sine coil 104 and cosine coil 106 are not ideal. As shown in
As illustrated in
As illustrated in
As illustrated in
These vias, combined with any non-uniformity in the magnetic fields generated in transmit coil 102, can result in nonlinearities, sometime large nonlinearities, in the operation of position sensor 100. When a position sensor is relatively long (bigger than 20 or /30 cm) there is a huge non-linearity in the position sensor due to the vias. This nonlinearity coming from the layout of receiver coils 104 and 106, such as that illustrated in
Ideally, the magnetic field at receive coils 104 and 106 is perpendicular to the plane of receive coils 104 and 106, which is the same as the plane of the top and bottom surfaces of PCB 108 on which traces forming receive coils 104 and 106 are formed. The physical phenomenal addressed by embodiments of the present invention result in non-linearity that is present because the electromagnetic field (EMF) generated by transmit coils 102 is not perfectly perpendicular to the plane of sine coil 104 and cosine coil 106. Consequently, there exists a component of the magnetic field that is parallel with the plane receive coils 104 and 106 (as defined by the top and bottom surfaces of PCB 108), and therefore is detected by loops formed by the vias in connection with traces 150 and 202, as is shown by loop 230 illustrated in
The area of loop 230, referred to herein as the “bad area”, is given by A=t*NDD. As discussed above, NDD is defined by the distance between vias while t is the thickness of PCB 108. In some common cases, PCB has a thickness t of 1mm, which is a typical value, and the area of loop 230 is given by A=NDD mm2. This area captures components of the magnetic field that are horizontal relative to the plane of receive coils 104 and 106 and with an X-Y component perpendicular to the area of loop 230. Consequently, from the Faraday-Neumann law an additional voltage will be generated in this area of the coils. In the example illustrated in
Consequently, loops formed by vias in each of areas 116, 118, 120, 122, and 124 can contribute to the voltage measured in receive coil 104. This additionally generated voltage is interpreted by a circuit coupled to receive voltage from receive coils 104 and 106 as a deformation of the “good signal”.
As discussed above, the “bad” vias effects in a receive coil such as coil 304 can be compensated by additional area 302 arranged in the same plane where receives coils including sine coil 304 are formed. The compensation area 302 can, for example, be created on the bottom of the PCB 108, in which case it is oriented perpendicular with the direction of the main magnetic field from transmitter coil 102. The compensation area 302 can compensate the effects of the vertical “bad area”, area 230 as illustrated in
Compensation area 230, which as shown in
The additional area of compensation area 302 can be designated as Comp_area. The bad area resulting from the vias, area 230, can be designated Bad_area and is equal to t*NDD, where t is the thickness of PCB 108. With the assumption that the fields are uniform, then the following relationship holds:
BZ*Comp_area=BN*Bad_area
The value of Comp_area can then be given by
Comp_area=(BN*Bad_area)/BZ=(BN/BZ)*Bad_area
The ratio (BN/BZ) can be estimated from a simulation tool given the layout of the transmission coils.
The above detailed description is provided to illustrate specific embodiments of the present invention and is not intended to be limiting. Numerous variations and modifications within the scope of the present invention are possible. The present invention is set forth in the following claims.