GB2191632A - Position sensor assemblies and methods for fabricating same - Google Patents

Description

SPECIFICATION Position sensor assemblies and methods for fabricating same The present invention relates generallyto position sensors and methods forfabricating such sensors. In particularthe present invention relates to position sensor arrangements which utilize integrated circuit technology and which employ rugged constructions suitable for adverse environments, such as internal combustion engines. Position sensors are employed in a wide variety of applications including uses in connection with internal combustion engines. For example, diesel engines typically employ needle or poppetvalves which are opened and closed attimed intervalsto inject desired amounts of fuel into the cylinderfor combustion. In order to maximize fuel efficiency and minimize undesirable exhaust emissions, it is desirableto detectthe operation ofthefuel injection element in relation to engine crankshaft position. The opening of the fuel injection element (i.e. needle valve, poppet valve, etc.) can then be set or controlled in timed relationship to the engine crankshaft position. In this regard, it is known that the initial displacement between the fuel injection element and its corresponding seat determines the beginning of injection. It is therefore necessary to time or control the initial displacement of the needle from the seat relative to the rotational position of the engine crankshaft, in orderto maximize fuel efficiency and reduce undesirable emissions. Similarly, geartooth sensors may be used to improve engine efficiency. 1 In United States Patents 4,359,895; 4,386,522; and 4,397,180,Wolff and Ziemacki disclose various valve position sensors for needle and poppetvalves employing a Hall-effect sensorfor detecting the movement of a magnet located with the needle or 1 poppet valve. Other prior art of interest includes the following United States patents: 3,913,537 to Ziesche, et al.; 3,605,703 to Moulds; 2,605,141 to Pyke,etal.; 4,046,112to Deckard; 4,161,161 to Bastenhof; 1 4,036,192 to Nakayama; 4,069,800 to Kanda, et al.; 3,952,711 to Kimberley, et al.; 3,921,604to Links; 4,050,431 toJackso; 3,796,206 to Links; 3,344,663to Dreisin, et al.; 4,096,841 to Kindermann, et al.; 3,416,506 to Steiger. Additionally, the following foreign patents are also of interest: Germany Auslegeschrift 1,049,635; British Patent Specifications 841,202 and 443,124; and French Patent 2,444,812. The above-referenced Wolff and Ziemacki patents 1 disclose numerous packaging configurations for electronic circuits employing a Hall-effect sensorfor measuring dynamic changes in a magneticfield due tothe magnet moving with a needle or poppet valve. Other prior art of interest with respectto integrated circuits in such an environment includes the following: "Impact of Silicon Substrates on Leakage Currents," Slotboom, et al., IEEE Electron Device Letters, Vol. EDL-4 No. 11, November, 1983; "Low Voltage Bipolar Circuits," by Derek Bray, Monochip Application NoteAPN-25, a publication of Interdesign, Inc.; and with respectto Hall-effect sensors, see The Hall-Effect and its Applications, C.L. Chein, etal., Plenum Press, New York, (1980), and particularly "The Hall-Effect in Silicon Circuits," an article therein byJ.T. Maupin,etal. Disclosed are constructions for position sensor assemblies, and methods forfabricating such assemblies. According to one aspect of the present invention there is provided a method forfabricating a position sensor, said method comprising the steps of: providing a lead frame having a predetermined pattern of contact surfaces, selected ones of the surfaces being connected to a corresponding lead; attaching mechanically an integrated circuit sensing element to the lead frame at the contact surfaces; bonding contact wires from selected ones of the contact surfaces to a corresponding contact pad on the integrated circuitsensing element; encapsulating the integrated circuit sensing element and contact surfaces in a first encapsulating mold to form an encapsulated assembly having a predetermined configuration including an elevated portion over each contact pad; severing each lead at a predetermined length;attaching each lead of the encapsulated assembly to a corresponding lead of a multi-lead wire; placing the encapsulated assembly and attached wire in a second encapsulating mold such that each elevated portion positions the assembly a predetermined distance from an end ofthesecond mold; and encapsulating the assembly and multi-lead wire to form an encapsulated sensor having the sensing element positioned a predetermined distance from a face of the sensor. According to another aspect of the present invention there is provided a position sensor assembly including an integrated circuit sensing element; a lead frame assembly having a plurality of leads of a predetermined length; electrically conductive means attaching contact pads on said integrated circuit sensing element to corresponding ones of said leads; a multi-lead wire having a plurality of lead wires, each of said lead wires having an end attached to a corresponding one of said leads of said lead frame assembly, and said multi-lead wire having a tube about said end; and encapsulation means about said sensing element, said lead frame assembly and in said tube at said end of said multi-lead wire. The position sensor assemblies are designed to be connected at one end of a multi-wire lead and incorporate a lead frame having a pair of leads which are electrically connected to respective wires atthe one end of the multi-wire lead. The sensor assembly constructions and methods forfabricating same are specifically adapted for use with a two-terminal integrated Hall-effect sensor circuit useful for sensing changes in a magneticfield outside ofthe circuit and providing an output representative ofthat change. The integrated circuit includes meansfor nulling the effects of any background magneticfields or noise. In one embodiment, atube is fitted axially about the one end of the multi-wire lead with encapsulation within the tube and aboutthe electrical connections between the lead frame and the wires of the multi-wire lead. The integrated electronic circuit described herein and which is used in connection with thetwo terminal configuration of the position sensor assemblies of the present invention is also described in U.S. Patent Application Serial Number633, 235, which is co-owned with this application and the above identified applications serial numbers 701, 935 and 776, 533. For a better understanding of the present invention, and to show howthe same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which :- Figure 1 is a top plan view of an integrated sensor mounted on a lead frame according to a first embodiment of the present invention, Figure 2 is a top plan view of the sensor of Figure 1 after a first encapsulation, Figure 3 is a side view of the sensor in Figure 2, Figure 4 is a partial cross-sectional view of the sensor according to Figures 1-3 positioned in a mold forthe second encapsulation process, Figure 5is a top plan view of an integrated sensor mounted on a lead frame according to a second embodiment of the present invention, Figures 6-10 are views similarto the views of Figures 2-4, and which illustrate the fabricating steps of the second embodiment,Figure 11 is a cross-sectional view of an integrated motion sensor according to another embodiment of the present invention, Figure 12 is a cross-sectional view of a sensor and magnet assembly, hollow cylindrical member, and connector blades enclosed in a quick connect-disconnect receptacle according to the embodiment of Figure 11, Figure 13 is a cross-sectional view of a geartooth sensor assembly obtained with two consecutive molding operations, Figure 14 illustrates protrusions extending from the sensing element and magnet assembly of Figures 11-13to center said assembly in the mold for injection molding during the fabricating process, Figure 15 is a block diagram illustrating an electronic sensing circuit in accordance with the present invention,

illustrating the electronic circuit of the present invention, and Figures 18,19 and 20 illustrate sequential steps in the processing of a portion of an electronic integrated circuit component in accordance with the present invention. Referring nowto Figure 1,there is illustrated a lead frame assembly having two contact surfaces 10 and 12 and two corresponding leads 14and 16 respectively. An integrated circuit device 18, preferably a Hall-effect sensor, is mounted upon the contact surfaces 10 and 12, but electrically isolated therefrom. The integrated circuit (IC) chip includes contact pads 20 and 22 which serve as electrical input and outputterminals forthe electrical circuit on the IC chip. Each of the contact pads 20 and 22 are electrically bonded to a corresponding one of the contact surfaces 10 and 12 of the lead frame assembly. Thewire bonding techniques for electrically connecting the contact pads and contact surfaces are well known in the art. The contact surfaces 10 and 12 and the associated leads 14and 16 are plated in order to facilitate the mechanical and electrical bonding of the chip 18to the lead frame assembly. This plating may be in the form of complete plating of the lead frame assembly or alternately the plating may be limited to only those areas of the lead frame assembly to which contact, either mechanical or electrical, is to be made. It should be noted that the chip 18 is mechanically mounted off center of the contact surfaces 10 and 12 in order to expose a sufficient portion of the lead frame surface for wire bonding. After the chip 18 has been mechanically and electrically bonded to the contact surfaces 10 and 12, the assembly is placed in a mold having a shape essentially as shown by the dashed lines 28. The assembly is then encapsulated, preferably using a transfer-molding insulating material. As will become apparent in the discussion of Figures 2 and 3, the mold has first and second depressions which are centered overthe contact wires 24 and 26 which will result in cone-shaped projections of the encapsulating material being formed overthese contact wires to protect the wires. Afterthe encapsulating material has set, the lead frame assembly and chip 18 are removed from the mold and the excess portion of the lead frame assembly trimmed away in a mannerwell known in the art. Referring now to Figure 2, there is shown atop view of the resulting encapsulated sensor assembly afterthe first step of encapsulation. The encapsulated assembly has radial corners 30 which lie on the circumference of an imaginary circle 32. The imaginary circle 32 represents a circle having a diameter about equal to the outside diameter of a multi-lead wire which is to be connected to the sensor assembly. The projections 34 and 36 formed overthe contact wires 24and 26 are also visible in Figure 2. The dashed lines 38 and 40 represent etched surfaces or perforations in the leads 14 and 16 respectively. As will become apparent, these etched lines are useful in defining the point at which the leads 14 and 16 can be bent. Such etching or perforations may be performed in the leads as part of the lead frame fabrication prior to encapsulation. Figure 3 is a side view of the sensor according to the present invention afterthefirst encapsulation process illustrated in Figure 2. The view in Figure better illustrates the projections 34 and 36 which preferably are cone shaped projections above the surface of the encapsulated sensor. The dashed lines 42 and 44 representthe position of the leads 14 and 16 after bending at the etched lines 38 and 40. The conical projections 34 and 36 fulfill the double function of protecting the wire bonds to the chip 18 during handling and also provide a positive stopfor the location of the assembly in the final mold forthe second encapsulation process. Referring nowto Figure 4, there is shown a partial cross-section of the inventive sensor assembly in a mold 46 forthe final encapsulation process. The leads 14 and 16 have now been bent in a direction perpendicularto the plane of the encapsulated chip 18. Lead wires 48 and 50 extend from a multi-lead wire or cable 52. The wires 48 and 50 are attached to the leads 14 and 16 bywelding, brazing orsoldering or other means well known in the art, in orderto make a positive electrical connection. The conical projections 34 and 36 serve as a guide for positioning the sensor assembly in the encapsulation mold 46. The projections 34 and 36 assure that the sensing device 18 is spaced a predetermined distance from the end surface of the final encapsulated sensor assembly.Forthe second encapsulation, the mold 46 containing the end of the wire cable 52 is filled with a transfer-mold insulating material which isthen allowed to set before removing the encapsulated assembly. It should be noted that the radial corners 30 abutthe sides of the mold cavity 54 in orderto position the first encapsulated sensor accurately within the cavity for the second encapsulation. After the second and final encapsulation, the sensor element and wire 52 constitute a single unit. Suitably, the final encapsulated sensor assembly is of a size to fit in the passageway corresponding to the passageway in a fuel injection nozzle (for example, see reference numeral 52 in U.S. Patent 4,386,522) and is positioned in the bottom of the passageway in a holder of a non-magnetic material such as stainless steel.The sensor works in conjunction with a permanent magnet also positioned in the fuel injection system such that the opening or closing of a fuel injection nozzle can be detected by relative movement of the magnet with respect to the sensor. Asecond embodiment of an integrated sensor and a related fabricating method will now be described with reference to Figures 5-8. Referring firstto Figure 5, there is shown an integrated circuit chip 118 on the associated lead frame, with two leads 114 and 116 connected to that lead frame, and which connection is severed after the first encapsulation in a manner similar to that described above with reference to Figure 1. Figure 5 also illustratesthe electrical connection ofthe integrated circuit chip 118 bywire bonding from the contact pads 120 and 122 to the contact surfaces 110 and 112. in the embodiment of Figures 5-10, and as is clearly illustrated in Figure 10,this embodiment includes an extension 160 which is inserted into the end of a tube 161 and extends from the lead frame and into the end ofthe multi-wire lead. The tube 161 is mounted, as shown in Figure 10, axially along the outside of the multi-lead wire 164.The extension 160 has two longitudinal cavities 162 and 163 formed during thefirst encapsulation to accommodate the insulated lead wires of the multi-wire lead, one of such lead wires being illustrated by reference numeral 164 in Figures 7 and 10. Thewire portion 165 of the lead wire 164 is welded to the bent lead 114, the other bent lead 116 likewise being welded to the other lead wire (notshown,for purpose of illustration). The cavities 162 and 163 are shaped such that both are closed off toward the inside of the tube 161 by the insulation of the lead wires 164,thus preventing the encapsulantfrom entering the tube during the second encapsulation. As is shown in Figure 10, the tube 161 has radial holes 166 and 167 therein. Those holes are preferably round, but any other shape is suitable. During the second encapsulation described above with reference to Figures 1-4, the encapsulantflows into the area 168, about the bent lead frame including leads 114 and 116, and thence into the cavities 162 and 163 and thereafter intothe holes 166 and 167. This secures and anchors the tube 161 to the second encapsulation. Preferably, the extension 160 of the first encapsulation has an outside diameter equivalentto the inside diameter of the tube 161 and has a chamfered end 172 permitting easy insertion into the tube 161. Stops 173 and 174 are provided on thefirst encapsulation, preventing the first encapsulation from being pushed too far into the tube 161; this avoids any difficulties resulting from an insufficient flow area forthe encapsulantto fill the cavities 170 and 171 and perforations 166 and 167. Another embodiment in accordance with the present invention will now be described with reference to Figures 11-14. Referring firstto Figure 11, there are illustrated two contact surfaces 210 and 212 and two corresponding leads 214 and 216, respectively. An integrated circuit device 18, preferably a Hall-effect sensor like that described below with reference to Figures 15-20, is mounted upon the contact surfaces 210 and 212, but electrically isolated therefrom. The integrated circuit (IC) chip includes contact pads 220 and 222 which serve as electrical input and outputterminals forthe electrical circuit on the IC chip. Each of the contact pads 220 and 222 are electrically connected to a corresponding one of the contact surfaces 210 and 212 by wire bonds. The wire bonding techniques for electrically connecting the contact pads and contact surfaces are well known in the art. The contact surfaces 210 and 212 and the associated leads 214 and 216 are plated in orderto facilitate the mechanical and electrical bonding of the chip 218to the lead frame. This plating may be in theform ofcomplete plating of the lead frame or alternately the plating may be limited to onlythose areas of the lead frame to which contact, either mechanical orelectrical, is to be made. It should be noted thatthe chip 218 is mechanically mounted off center of the contact surfaces 210 and 212 in orderto expose a sufficient portion of the lead frame surface for wire bonding. Afterthe chip 218 has been mechanically and electrically connected to the contact surfaces 210 and 212, the assembly is placed in a mold having a shape essentially as hatched and with a contour as shown by line 228. The assembly isthen encapsulated, preferably using a transfer-molding insulating material. The insulating material forms a planar surface 230, near the chip 2.1 8 for the bonding of a magnet 232. The magnet 232 is bonded to the surface sothat magnetic flux lines caused by the proximity of the gear tooth 234 pass through a Hall-effect sensor in chip 218. The strength of the magnetic field generated by the magnet is chosen in orderthatthe electronic circuit of the chip 218 can null the effects of the residual magneticfield and still measure any changes in the magneticfield due to the movement ofthe geartooth. The moving magneto-responsive material ofthegeartooth moving by the Hall-effect cell of chip 218 causes a flux increase in the magnetic field sensed by the cell. Theterm magneto-responsive is used to denote any material that has a higher conductivity to magnetic flux than air and is attracted by a magnet. The Hall-effect sensor senses the change in the magneticfield, and if the change exceeds the chip 218 threshold, the chip 218 switches and changes its resistance. This causes a change in the current flow of the chip 218 which is detected by a sensor output responsive circuit. The sensor output responsive circuit is preferably part of or connected to a microprocessor system. Asthegeartooth continues its movement, the magnetic field decreases and the sensor switches again, reverting to its former resistance, which change is again detected by the output responsive circuit. In this way, the instantaneous position of the geartooth can be determined. The same event happens as each consecutive gear tooth moves pastthe sensor, thereby causing a series of electrical pulses whose frequency is then indicative of the peripheral speed of the gear. Thus, the peripheral speed of the gear can also be measured in a manner well known in the art. The leads 214 and 216 are bent in a direction perpendicularto the plane of the encapsulated chip 218. Lead wires 248 and 250 extend from a multi-lead wire or cable 252 as shown in Figure 12. The wires 248 and 250 are attached to the leads 214 and 216 by welding, brazing orsoldering orothermeanswell known in the artfor making a positive electrical connection. Forthe second encapsulation, the end of wire cable 252 is connected to connector blades, as will be described later. The first encapsulation covers the chip 218, contact pads 220, 222 and a portion of the lead frame, and forms the sensing element. The second encapsulation encloses the sensing element, the leads 214 and 216, the magnet 232 and a portion of the connecting leads 248 and 250, and forms the sensing element and magnet assembly 242. The connecting leads are attached to a multi-lead wire as will be described with respect to Figure 12. There is also shown an air gap 238which is the distance between the sensing element and magnet assembly 242 and the geartooth 234. Also shown is a flux concentrator 136 that acts as a pole piece to concentrate the magneticfield in a manner well known in the art. Figure 12 showsthe sensing element and magnetic assembly as described in Figure 11 inserted into a hollow cylindrical threaded member 244. The member244 is manufactured of non-magnetic material. The multi-lead wire cable 252 passes through the hollow cylindrical member and is connected to respective connector blades 246. The wire cable is connected to the connecting leads 248 and 250 and to the corresponding connector blades bywelding, brazing or soldering. The sensing element and magnet assembly is fixed in the end of the cylindrical member 244, so that the Hall-effect sensor in the chip lies on the longitudinal axis of the cylindrical member 244, and is coterminouswith the end of the hollow member. In this position, the rotation of the cylindrical member 244 will not affect the position of the Hall-effect sensor. Since the cylindrical member 244 may rotate during positioning about the Hall-effect sensor, the rotational movement of the cylindrical member 244 does not affectthe flux measurements of the geartooth sensor assembly. The position of the Hall-effect sensor is very important, since a positional change often can cause inaccurate measurements of the instantaneous position of the gea r tooth. The third encapsulation forms the unit as shown by the hatched area. The unit encloses a portion of the cylindrical member 244 and the connector blades 246to form a solid unified body. The material is resilient enough to support a quick connect-disconnect connector coupled to the connector blades. The molded unit 247 forms a male quick connect-disconnect unit in a mannerwell known in the art. Referring again to Figure 12, there is described a sensor assembly requiring three consecutive molding operations. In the alternative, the first and the second molding operation can be combined by either attaching the magnet to the lead frame at the time the Hall-effect IC is attached to it or inserting the magnets into the mold priorto the lead frame atthe time the Hall-effect IC is attached to it and encapsulating the Hall-effect IC chip assembly and the magnet in one operation. The encapsulated sensing element and magnet assembly as shown in Figure 14 is preferably formed with protrusions 256 which locate and center the sensing element in the mold forthe consecutive injection molding operation. Referring to Figure 13, the injection molding operation forms the total geartooth sensor assembly 254 including the threaded cylindrical part 258. The multi-lead wires 252 are electrically connected to the connector blades as described before, and the geartooth sensor assembly 254 comprises the sensing element and magnet assembly 242, the multi-lead wires 252 and the connector blades 246. The encapsulation process forms a unified solid body with the sensing element on one end and the quick connect-disconnect connector on the other. This embodiment of the invention is more cost effective for high volume production. The sensing element and magnet assembly, cylindrical member, and third encapsulation form a single unitwhich can serve asthe geartooth sensor assemblyforan internal combustion engine. The geartooth sensor assembly may be inserted into an internal combustion engine orthe like by an appropriate means such as screwing into the timing gear housing, with the connector blades connected to an appropriate signal processing circuit, such as an oscilloscope or a microprocessor system. As a gear-tooth or other magneto-responsive material passes in front ofthe Hall-effect integrated circuit, the tooth acts as a flux concentrator, increasing the magneticfield over a "no-tooth" condition. Since the integrated circuit is sensitive to the change in magnetic field, it is responsive to the leading and trailing edge of the geartooth. Thus, the instant position can be easily determined by sensing the frequency of the signal. The integrated circuit preferably includes a Hall-effect sensorforsensing a change in a magnetic field external to the circuit and providing an output representative of the change in the magnetic field. A suitable integrated Hall-effect sensor is fully disclosed in United States Patent Application 633,235filed July 23,1984, which is commonly owned with this application and the above-identified applications Serial Numbers 701,935 and 776,533. The Hall-effect sensor is also fully disclosed below with reference to Figures 15-20. Briefly, however, circuit means are electronically coupled with the output of the sensing means for providing an output indicating the presence of the magneticfield change.A low current circuit is coupled with the output of the sensing means and across the indicating circuit means for nulling the electronic circuit responsiveto the sensing means output, to thereby eliminate the influence of static magnetic fields generated by the permanent magnet and any extrinsic magnetic fields. The nulling circuit operates at a very low current range, on the order of 2 to 3 nanoamperes, in conjunction with a capacitor coupled to the output of the low current nulling circuit, and with means for charging and discharging the capacitor responsive to any imbalance of the inputto the indicating circuit means. The electronic circuit is designed to perform the function of sensing a magnetic pulse while ignoring any background field, and operates without external components in atwoterminal configuration overa wide temperature range. In connection with this function, the circuit is integrated into a monolithic semiconductor body utilizing a geometry with very low leakage transistors, in orderto obtain very low current characteristics. Both the indicating circuit and the low current nulling circuit comprise comparators formed by planartransistors in a single monolithic semiconductor body, and in which low junction leakage chracteristics are obtained with a specific semiconductor region configuration and the utilization of a highly doped base region extending outwardly and overlapping the base-collector junction in at least a portion of the base region.This feature is employed together with a highly doped substrate to achieve the low junction leakage characteristics. The magnetic sensing means comprises a Hall-Effect sensor integrated with the electronic circuit in the monolithic semiconductor body, and with the outputthereof coupled with an amplifier which in turn provides outputs responsive to changes in the magneticfield as detected by the sensor, and which outputs are in turn provided to the indicating circuit and nulling circuitfunctions. Referring now to Figures 15-20, there is disclosed a two-terminal integrated Hall-effect sensor circuit useful with the sensor arrangements of Figures 1-14 and the aforementioned applications Serial Numbers 701,935 and 776,533, as well as the header, lead and package configurations taught in U.S. Patents 4,359,895; 4,366,706; 4,386,522; and 4,397,180 to Wolff or to Wolff and Ziemacki. Referring firstto Figure 15, there is shown an electronic circuit for dynamically sensing and processing signals representative of changes in a magneticfield. While the circuit 31 0 of Figure 15 may take the form of discrete circuit components, it is preferred that the entire circuit be integrated in a single monolithic semiconductor body, except for certain external components, as described in greater detail below. The circuit 310 in accordance with the present invention includes a Hall-effect sensor 312 having a function similar to the Hall-effectsensor344 disclosed in the aforementioned U.S. Patent 4,359,895 to Wolff and Ziemacki (note Figures 2 and 3 of that patent). Temperature compensating diodes 14 are connected in series with the Hall sensor 312. An amplifier 316 is coupled across the two terminal output of the Hall-effect sensor 312, and in turn has a positive and negative output, A and B, respectively. Outputs A and B from amplifier 316 form an inputto comparator circuits 318 and 320, which are coupled in parallel to the respective outputs in the manner shown in Figure 15. An impedance matching circuit 322 is coupled to each inputto comparator 318 in orderto prevent impedance loading of comparator 320 and amplifier 316 by comparator 318. As will be described in greater detail below, comparator 320 relies on very low current characteristics in order to function as a nulling circuitforthe entire electronic system 310. The output of comparator 318 is coupled to the base of an output transistor 324, which is shunted by a high frequency roll-over limiting capacitor 326.A load impedance 328 is coupled in series with transistor 324 between output terminals 332 and 330. As is described in greater detail below, terminals 332 and 330 (supply and ground respectively) form the only input and output terminal connections to the circuit 310, which greatly simplifies its operation. An external current sensing resistor 334 is also provided in connection with the operation of the circuit 310. Referring again to the input A to comparator 318, there is shown an offset impedance 336 between the impedance matching circuit 322 and the inputto comparator 318. This offset resistance 336 determines the threshold for changes in the magneticfield, which typically would be adjusted in orderto permit the sensing of changes in the magnetic field on the order of 30 to 200 Gauss. Current sources 11 and 12 are shunted across respective outputs Aand B ofthe amplifier atthe input side of comparator 318. Thefunction and makeup of these current sources 11 and 12 will be more fully described belowwith reference to Figures 16 and 17; however, for purposes of this discussion, it should be noted that current sources 11 and 12 require a negative temperature coefficient. Attention is now directed to the nulling circuit connected to the output of comparator 320 for controlling the voltage at outputA of amplifier 316.The function of the nulling circuitoutput istoforma feedback loop that constantly seeks to null the voltage out of output A for amplifier316, and thereby avoid effects caused by ambient magneticfields, temperature variations and deviations in processing of the integrated circuit in which this circuit is constructed, as is shown in Figures 18 through 20 and described belowin detail. The nulling circuit includes a capacitor338 shunted between the output of comparator 320 and ground. A series-connected transistor 342 and nulling impedance 344 are shunted between the output A and ground, with the base of transistor 342 coupled to the output of comparator 320 through a nulling impedance matching circuit340. In operation,the nulling rate is constant, but dependent upon the values and characteristics of the various components forming the nulling circuit.As will be appreciated,the nulling circuit serves to control the feedback loop between outputAof amplifier 316 and ground, as that current passes through transistor 342. In accordance with the present invention, the current level atthe output of comparator 320 is on the order of 2 to nanoamperes, and thus the characteristics of the transistors which form the comparator 320 require exceptionally low junction leakage characteristics. Attention is now drawn to Figures 16and 17, which more specifically illustrate schematically the electronic circuit of Figure 15. Noting the left-middle portion of Figure 16, there is illustrated the Hall-effect sensor 312, and temperature compensating diodes 314. The amplifier316 of Figure 15 is made up ofthefollowing circuit components: transistors Q1 and Q2, resistors R1 - R4 and current source 13. Current source 13, as shown in Figure 17, consists of transistor Q2 and resistor R16. Typically, current source 13 provides a current on the order of 147 microamperes. Now noting the right-middle portion of Figure 16, the comparator 318 is characterized by transistors Q7, Q8, Q103 and Q104. Current sources 11 and 12, as shown in Figure 17, consist of transistors Q12 and Q13. resistors R14 and R15 and diodes D10 and D11. Typically, current sources 11 and 12 provide a current on the order of 30 microamperes. Impedance matching circuit322 of Figure 15 is defined by transistors Q3 and Q4 in the upper right-middle of Figure 16. The output driver section of the electronic circuit 310 of Figure 15 includes transistors Q14 and Q15 (note extreme right hand portion of Figure 16), togetherwith capacitor 326 and resistor R7; it will be understood that transistors Q14 and Q15form the circuit defined by transistor 324 of Figure 15. Current source 14 is connected to the driver section of the circuit between transistors Q14 and Q15, and is shown more particularly in Figure 17 where current source 14 is defined by transistor Q31 and Q32. Attention is now drawn to the very center of Figure 16. Comparator 320 of Figure 15 is defined by transistors Q5, Q6, Q101 and 0102, together with current source 15. As shown in Figure 17, current source 15 is defined by transistors Q25 (a multiple collectortransistorfor beta compensation) and Q23. Typically, current source 15 provides a current input to comparator320 on the order of about 2 nanoamperes,forthe reasons discussed above. Temperature and supply compensation with respect to current source 15 is provided by the combinations of transistors Q15, Q22, diode D21, and associated resistors as shown in Figure 17. PNP beta compensation of transistor Q25 is provided by an identical multi-collectortransistorQ20. Reference is now made to the extreme left hand portion of Figure 16, where there is depicted the nulling circuit. The nulling circuit includes capacitors C1, which is the nulling capacitor 338 of Figure 15. Outputs ofamplifier316 are shown in Figure 16 by the same designations, that is points A and B. The nulling circuit includes transistors Q9, Q11, Q12, Q13 and 0105, together with diode D12 and resistorR5. The nulling circuit includes two current sources, 16, and 17, which are more particularly shown in Figure 17. Current source 16 includes transistor 024, the base of which is coupled across transistor Q22 and associated resistors. Typically, current source 16 is on the order of3nanoamperes. Current source 17, as shown in Figure 17, is defined by transistor Q17 and Q1 8, which typically provide a current on the order of 0.1 microamperes. Current source 15 is coupled to the high side of transistors 0101 and Q102 in comparator 320 (note the top middle portion of Figure 16). Similarly, current source 18 is coupled to the high side of comparator 318 to transistors Q103 and Q104, and is defined by transistor 07 in Figure 17. Typically, current source 18 provides a current input on the order of about 10 microamperes. A construction of the electrical circuit 310 of Figures 15-17 in an integrated circuit configuration will now be described with reference to Figures 1820. As shown in Figure 18, the starting material is typically a monolithic silicon wafer having a 1-1-1 orientation off 4[deg] 0.5[deg]and on the order of 10 mils thick. As shown, the monolithic wafer 350 has upper and lower surfaces 351 and 353, respectively, and is highly doped to the order of about .08-.25 ohm-cm. A relatively highly doped N buried collector region 352 is diffused into the upper surface 353 of the monolithic chip 350, having a doping level about 1020. Next, an epitaxial layer of silicon is grown on the upper surface 353 of the monolithic chip 350. In accordance with this invention, the epitaxial layer 356 comprises a lightly doped N region having a concentration on the order of 2x 1 016. Deposition of layer356 results in the spreading of the buried portion of the collector region 352 upwardly, as shown at 354. Referring nowto Figure 19, a P+ isolation ring 358 and an N+ collector contacting region 360 are diffused from the top surface of the epitaxial layer 356 into that layer. Typically, the collector ring 360 is diffused down to the buried N+ region 354. Next, a moderately doped base region 362 is diffused from the upper surface of the epitaxial layer into the relatively lightly doped N region 356 of the collector. In accordance with this invention, the interface of the moderately doped P+ region 362, which interface is designated as element 363, overlaps and extends into the collector ring 360. Typically, the moderately doped P+ base contact region 362 has a doping concentration on the order of 1 018, and a sheet resistivity on the order of 150-400 ohms/sq. Now referring to Figure 20, a relatively high doped emitter region 364 is diffused into the base contact region 362 from the upper surface of the epitaxial layer 356. Typically, the emitter region 364 has a doping level on the order of 10 . While notshown, it will be understood that the various diffusion techniques described above require the opening of diffusion passageways in a silicon dioxide layer on the upper surface of the epitaxial layer 356, and that the opening of those passageways controls the location of the various planar regions 358, 360, 362 and 364. Further, while not shown, as a final step the last silicon dioxide layer may be opened up to permit metalization patterns to be deposited in orderto make contact to the various regions as desired. When the various transistors of the comparators 318 and 322 and the null circuit are fabricated in a monolithic integrated circuit in accordance with the diffusion profile and geometry of Figures 18-20, the resulting transistors are provided with a junction leakage current characteristic on the order of about 0.2 nanoamperes maximum, under non-operating conditions and at maximum operating temperatures (on the order of 125[deg]C). This characteristic permits the nulling circuit of Figure 15 to null the current out of pointA of amplifier316with extraordinary low current characteristics, This in turn permitsthe entire circuit 310 of Figure 15 to detect relatively small changes in the ambient magnetic field, as noted above, on the order of about 10 to 200 Gauss. More particularly, the circuit 310 of Figure 15 is capable of performing thefunction of sensing a magnetic pulse on the order discussed above, while ignoring the background field. Further, the circuit 310 operates without significant external components in a two-terminal configuration, over a wide temperature range, all while requiring very low (nanoamperes) currents and while incorporating the circuit310 in a monolithic integrated circuit and permitting the use of an on-chip metal-oxide-semiconductor capacitorfor use as a nulling capacitor338. The current source forthe nulling stage associated with comparator320 of Figure 15 achieves reduced power sensitivity, temperature compensation and reduced supply sensitivity to transistor beta variations, which together with the features of the nulling circuit and the transistors associated with the comparators 318 and 320, permits the comparator 320 to operate at 2 to 3 nanoamperes ranges. The two-terminal configuration of the circuit 310 of Figure 15, in which terminal 332 provides supply and terminal 330 is ground, utilizes the external resistor 334 to provide hysteresis to prevent chatter, by adding positive feedback to the Hall-effect sensor 312. This occurs because the signal increases as the circuit operates, increasing the voltage across the Hall-effect sensor 312, thereby increasing its output which is proportional to the voltage across it.In operation, the signal from the Hall-effect sensor 312 is first amplified byamplifier316which operates in a linear temperature compensated differential mode. The switching threshold between comparator 318 and the output of amplifier 316 is accomplished using emitterfollowers between the amplifier316 and the output comparator 318 (note Figure 16) and the offset generating resistor 336 coupled to the pointA output of amplifier316. Temperature compensation is accomplished with the associated current source. Thus, the electronic circuit 310 of Figure 15, which is shown in greater detail in Figures 16 and 17, provides a means for dynamically sensing and processing signals representative of changes in a magneticfield.

Claims (18)

1. A method forfabricating a position sensor, said method comprising the steps of: providing a lead frame having a predetermined pattern of contact surfaces, selected ones of the surfaces being connected to a corresponding lead; attaching mechanically an integrated circuit sensing elementto the lead frame atthe contact surfaces; bonding contact wires from selected ones of the contact surfaces to a corresponding contact pad on the integrated circuit sensing element; encapsulating the integrated circuit sensing element and contact surfaces in a first encapsulating mold to form an encapsulated assembly having a predetermined configuration including an elevated portion over each contact pad; severing each lead at a predetermined length; attaching each lead of the encapsulated assembly to a corresponding lead of a multi-lead wire; placing the encapsulated assembly and attached wire in a second encapsulating mold such that each elevated portion positions the assembly a predetermined distance from an end of the second mold; and encapsulating the assembly and multi-lead wire to form an encapsulated sensor having the sensing element positioned a predetermined distancefrom a face of the sensor.

2. A method according to claim 1, wherein the step of attaching the multi-lead wire includes the steps of: bending each lead of the encapsulated assembly substantially perpendicularly to a plane of a surface of the integrated circuit sensing element; and welding each lead to a corresponding lead of the multi-lead wire.

3. A method according to clajm 2, including the steps of: providing a tube about said multi-lead wire atthe extremity thereof; forming a longitudinal void in one end of said multi-lead wire adjacent said lead frame and positioning at least one of said welded leads in said void; and flowing said encapsulation into said void and about said welded lead during said second encapsulation step.

4. A method according to claim 3, including the steps of: forming at least one hole radially in said tube at an end thereof adjacent said void and in communication therewith; and flowing said encapsulation into said hole during said second encapsulation step.

5. A position sensor assembly including: an integrated circuit sensing element; a lead frame assembly having a plurality of leads of a predetermined length; electrically conductive means attaching contact pads on said integrated circuit sensing elementto corresponding ones of said leads; a multi-lead wire having a plurality of lead wires, each of said lead wires having an end attached to a corresponding one of said leads of said lead frame assembly, and said multi-lead wire having a tube about said end; and encapsulation means about said sensing element, said lead frame assembly and in said tube at said end of said multi-lead wire.

6. Asensorassemblyaccordingtoclaim5, wherein said sensing element comprises a Hall-effect sensor.

7. A sensor assembly according to claim 6, wherein each of said leads of said lead frame assembly are perpendicularto a plane of a surface of said sensing element.

8. A sensor assembly for detecting the position of a magneto-responsive mass, said sensor assembly comprising: (a) a two terminal integrated circuit with an integrated Hall-effectsensorforsensing any changes in magneticfluxfrom said mass; (b) a leadframe having a plurality of leads; (c) means electrically connecting saidtwo terminals of said circuit to corresponding leads of said leadframe; and (d) encapsulating means about said sensing means and at least a portion of said leads.

9. An assembly according to claim 8, including means with said circuit and said lead framefor generating a magneticfield.

10. An assembly according to claim 8, including a multi-wire lead, each of said wires of said lead having an end attached to a corresponding lead from said leadframe.

11. A method for sensing the position of member having a magneto-responsive mass, said method including the steps of: (a) positioning an electronic circuit having a nulling circuit and a Hall-effect sensing element capable of measuring a change in a magneticfield between said member and said circuit; (b) generating a changing magneticfield between the member and the Hall-effect sensor; (c) eliminating the effects of any background residual magneticfield by means of said nulling circuit; and (d) sensing the magnetic field change due to the movement of said member.

12. A method according to claim 11, including the steps of: providing said electronic circuit with two terminals; providing a lead frame having two leads and electrically attaching said two circuit terminals to said two leads; and contouring said lead frame and said leads so asto befastenable atthe end of a multi-wire lead, so that said sensor assembly may be positioned within narrow confines.

13. A sensor assembly having an electronic circuit for detecting the position of a magneto-responsive mass moving with respectto the sensor assembly, said sensor assembly comprising: (a) a two-terminal integrated circuit having an integrated Hall-effect sensorfor sensing a change in a magneticfield extrinsicto said circuitand providing an output representative of said change; (b) a lead frame with two leads electronically coupled with said two terminals of said circuit; (c) a permanent magnet generating a static magneticfield and mounted with said leads and said circuit; (d) a multi-wire lead with said lead frame mounted on one end thereof with said each of said leads of said lead frame electrically connected to one wire of said multi-wire leads; (e) meansfor encapsulating and surrounding said meansforsensing, said leads and said permanent magnet, and forming a sensing element and magnet assembly; and wherein (f) said circuit includes meansfor nulling the effects of any background noise.

14. A sensor assembly according to claim 13, including a tube axially about the outside periphery of said multi-wire lead at said one end thereof, and encapsulation within said tube and surrounding said connection between said leads of said lead frame and said wires.

15. A sensor assembly according to claim 14, including an extension from said lead frame and extending axially into said one end of said one-end of said multi-wire lead, said encapsulation surrounding said extension.

16. Asensorassemblyaccordingtoclaim15, including radial holes in said tube beyond said one end of said multi-wire lead with said encapsulation extending through and anchored in said holes.

17. A method forfabricating a position sensor substantially as hereinbefore described with reference to the accompanying drawings.

18. A position sensor assembly substantially as hereinbefore described and as illustrated in Figures 1 to 4, Figures 5to 10, Figures 11 to 14, Figure 15, Figures 16 and 17 or Figures 18to 20 of the accompanying drawings.