Patent Grant
8818749
Not Applicable.
This invention relates generally to magnetic field sensors and, more particularly, to a magnetic field sensors having a self-test capability.
As is known, there are a variety of types of magnetic field sensing elements, including, but not limited to, Hall effect elements, magnetoresistance elements, and magnetotransistors. As is also known, there are different types of Hall effect elements, for example, a planar Hall element, a vertical Hall element, and a circular Hall element. As is also known, there are different types of magnetoresistance elements, for example, a giant magnetoresistance (GMR) element, an anisotropic magnetoresistance element (AMR), a tunneling magnetoresistance (TMR) element, and a magnetic tunnel junction (MTJ).
Hall effect elements generate an output voltage proportional to a magnetic field. In contrast, magnetoresistance elements change resistance in proportion to a magnetic field. In a circuit, an electrical current can be directed through the magnetoresistance element, thereby generating a voltage output signal proportional to the magnetic field.
Magnetic field sensors, i.e., circuits that use magnetic field sensing elements, are used in a variety of applications, including, but not limited to, a current sensor that senses a magnetic field generated by a current carried by a current-carrying conductor, a magnetic switch that senses the proximity of a ferromagnetic object, a rotation detector that senses passing ferromagnetic articles, for example magnetic domains of a ring magnet, and a magnetic field sensor that senses a magnetic field density of a magnetic field.
As is known, some integrated circuits have internal built-in self-test (BIST) capabilities. A built-in self-test is a function that can verify all or a portion of the internal functionality of an integrated circuit. Some types of integrated circuits have built-in self-test circuits built directly onto the integrated circuit die. Typically, the built-in self-test is activated by external means, for example, a signal communicated from outside the integrated circuit to dedicated pins or ports on the integrated circuit. For example, an integrated circuit that has a memory portion can include a built-in self-test circuit, which can be activated by a self-test signal communicated from outside the integrated circuit. The built-in self-test circuit can test the memory portion of the integrated circuit in response to the self-test signal.
Conventional built-in self-test circuits tend not to allow the integrated circuit to perform its intended function while the built-in self-test is being performed. Instead, during the built-in self-test, the built-in self-test circuit exercises all of, or parts of, circuits on the integrated circuit in particular ways that do not necessarily allow concurrent operation of functions that the integrated circuit is intended to perform. Therefore, the built-in self-test is typically only activated one time, for example, upon power up of the integrated circuit, or from time to time. At other times, the built-in self-test circuit and function are dormant and the integrated circuit can perform its intended function.
Furthermore, when used in magnetic field sensors, conventional built-in self-test circuits tend not to test the magnetic field sensing element used in the magnetic field sensor.
It would be desirable to provide built in self-test circuits and techniques in a magnetic field sensor that allow the self-test to be run from time to time or upon command while the magnetic field sensor concurrently performs its intended function. It would also be desirable to provide such a concurrent self-test that tests a magnetic field sensing element used within the magnetic field sensor.
The present invention provides self-test circuits and techniques in a magnetic field sensor that allow the self-test to be run from time to time or upon command while the magnetic field sensor concurrently performs its intended function. The present invention also provides such a concurrent self-test that tests a magnetic field sensing element used within the magnetic field sensor.
In accordance with one aspect of the present invention, a magnetic field sensor includes a magnetic field sensing element supported by a substrate. The magnetic field sensing element is for generating a composite magnetic field signal having a measured-magnetic-field-responsive signal portion and a self-test-responsive signal portion. The measured-magnetic-field-responsive signal portion is responsive to a measured magnetic field. The self-test-responsive signal portion is responsive to a self-test magnetic field. The magnetic field sensor also includes a self-test circuit having a self-test current conductor proximate to the magnetic field sensing element. The self-test current conductor is for carrying a self-test current to generate the self-test magnetic field. The magnetic field sensor also includes a processing circuit coupled to receive a signal representative of the composite magnetic field signal. The processing circuit is configured to generate a sensor signal representative of the measured-magnetic-field-responsive signal portion. The processing circuit is also configured to generate at least one of a diagnostic signal representative of the self-test-responsive signal portion or a composite signal representative of both the measured-magnetic-field-responsive signal portion and the self-test-responsive signal portion.
In accordance with another aspect of the present invention, a method of generating a self-test of a magnetic field sensor includes generating, with a magnetic field sensing element, a composite magnetic field signal comprising a measured-magnetic-field-responsive signal portion and a self-test-responsive signal portion. The measured-magnetic-field-responsive signal portion is responsive to a measured magnetic field. The self-test-responsive signal portion is responsive to a self-test magnetic field. The method also includes generating a self-test current in a self-test current conductor proximate to the magnetic field sensing element. The self-test current conductor is for carrying the self-test current to generate the self-test magnetic field. The method also includes generating a sensor output signal representative of the measured-magnetic-field-responsive signal portion. The method also includes generating at least one of a diagnostic signal representative of the self-test-responsive signal portion or a composite signal representative of both the measured-magnetic-field-responsive signal portion and the self-test-responsive signal portion.
The foregoing features of the invention, as well as the invention itself may be more fully understood from the following detailed description of the drawings, in which:
Before describing the present invention, some introductory concepts and terminology are explained. As used herein, the term “magnetic field sensing element” is used to describe a variety of electronic elements that can sense a magnetic field. The magnetic field sensing elements can be, but are not limited to, Hall effect elements, magnetoresistance elements, or magnetotransistors. As is known, there are different types of Hall effect elements, for example, a planar Hall element, a vertical Hall element, and a circular Hall element. As is also known, there are different types of magnetoresistance elements, for example, a giant magnetoresistance (GMR) element, an anisotropic magnetoresistance element (AMR), a tunneling magnetoresistance (TMR) element, an Indium antimonide (InSb) sensor, and a magnetic tunnel junction (MTJ).
As is known, some of the above-described magnetic field sensing elements tend to have an axis of maximum sensitivity parallel to a substrate that supports the magnetic field sensing element, and others of the above-described magnetic field sensing elements tend to have an axis of maximum sensitivity perpendicular to a substrate that supports the magnetic field sensing element. In particular, most types of magnetoresistance elements tend to have axes of maximum sensitivity parallel to the substrate and most types of Hall elements tend to have axes of sensitivity perpendicular to a substrate.
As used herein, the term “magnetic field sensor” is used to describe a circuit that includes a magnetic field sensing element. Magnetic field sensors are used in a variety of applications, including, but not limited to, a current sensor that senses a magnetic field generated by a current carried by a current-carrying conductor, a magnetic switch that senses the proximity of a ferromagnetic object, a rotation detector that senses passing ferromagnetic articles, for example, magnetic domains of a ring magnet, and a magnetic field sensor that senses a magnetic field density of a magnetic field.
Referring to
In some embodiments, the self-test magnetic field is within a range of about twenty to forty Gauss. However in other embodiments, the self-test magnetic field can be smaller than twenty Gauss or greater than forty Gauss.
The magnetic field sensor 10 can include power and bias and driver circuits 22. The power and bias and driver circuits 22 can include a circuit power and bias module 28 configured to provide various voltages and currents to the rest of the circuitry within the magnetic field sensor 10. The power and bias and driver circuits 22 can also include a sensor element driver module 26 (e.g., a current source) configured, for example, to generate a current signal 26a coupled to the magnetic field sensing element 32. The power and bias and driver circuits 22 can also include a coil driver module 24 (e.g., a current source) configured to generate a current signal 24a coupled to the self-test current conductor 30. However, in other embodiments, an external coil driver module, apart from the integrated circuit 10 can be used.
The magnetic field sensor 10 can also include a diagnostic request processor 58 coupled to receive a diagnostic input signal (Diag_In) 23. The diagnostic request processor 58 is described more fully below in conjunction with
The processing circuit 34 (also referred to herein as a signal processor 34) can include a processing module 36 having either an analog signal processor 38, a digital signal processor 40, or any combination of analog and digital processors 38, 40 that perform any combination of analog and digital processing of the composite magnetic field signal 32a. The arrow shown between the analog signal processor 38 and the digital signal processor 40 is used merely to indicate the combination of analog and digital signal processing and various couplings therebetween.
The signal processor 34 can also include a gain adjustment module 42, an offset adjustment module 44, and a temperature adjustment module 46, each coupled to the processing module 36. The gain adjustment module 42 is configured to contribute to a signal 48 received by the processing module 36, which signal 48 is configured to adjust or calibrate a gain of the processing module 36. The offset adjustment module 44 is also configured to contribute to the signal 48 received by the processing module 36, which signal 48 is also configured to adjust or calibrate a DC offset of the processing module 36. The temperature adjustment module 46 is also configured to contribute to the signal 48 received by the processing module 36, which signal 48 is configured to adjust or calibrate a gain and/or a DC offset of the processing module 36 over temperature excursions. It will be understood that that gain, offset, and temperature are but some common parameters that are compensated/adjusted, but that compensation/adjustment is not limited to those parameters only.
The processing module 36 is configured to generate the sensor signal 36a representative of the above-described measured-magnetic-field-responsive signal portion. The processing module 36 is also configured to generate at least one of the diagnostic signal 36c representative of the above-described self-test-responsive signal portion or the composite signal 36b representative of both the measured-magnetic-field-responsive signal portion and the self-test-responsive signal portion.
In some embodiments, the magnetic field sensor 10 can also include output circuits 50, for example, a sensor output formatting circuit 52, a diagnostic output formatting circuit 56, and a combining circuit 54. Operation of the sensor output formatting circuit 52, the diagnostic output formatting circuit 56, and the combining circuit 54 will be further understood from discussion below in conjunction with
The magnetic field sensor 10 can also provide an external coil drive signal 16 and an external ground 20, which can be coupled to an external conductor or coil 18. The coil 18 can be used in place of the self-test current conductor 30 to generate the above-described self-test magnetic field.
In operation, the current signal 24a can be a pulse signal, and therefore, the self-test magnetic field can be a pulsed magnetic field generated by the self-test current conductor 30 or by the external coil 18. The self-test magnetic field can physically combine with the above-described measured magnetic field, which is a field associated with that which the magnetic field sensor 10 is intended to measure. For example, the magnetic field sensor 10 can be intended to measure a magnetic field associated with a ferromagnetic or magnetic object, which generates the measured magnetic field. For another example, the magnetic field sensor 10 can be intended to measure a current flowing in a conductor (not shown), which generates the measured magnetic field.
In operation, the combination of the measured magnetic field and the self-test magnetic field is received by the magnetic field sensing element 32. The self-test magnetic field can be initiated by way of the diagnostic input signal 23, described more fully below in conjunction with
In some embodiments, the processing circuit 36 can operate to separate the measured-magnetic-field-responsive signal portion from the self-test-responsive signal portion to generate the sensor signal 36a representative of the magnetic field-signal portion and the diagnostic signal 36c representative of the self-test-responsive signal portion. However, in some embodiments, the processing circuit can generate the composite signal 36b representative of both the measured-magnetic-field-responsive signal portion and the self-test-responsive signal portion in addition to or in place of the signal 36c.
In operation the output circuits 50 can reformat the signals 36a-36c into at least the formats described below in conjunction with
Referring now to
The self-test magnetic field 60a can be a pulsed magnetic field generated by a pulsed current carried by the self-test current conductor 30′. The self-test magnetic field 60a physically adds to any other magnetic field (not shown), e.g., the measured magnetic field, experienced by the magnetic field sensing element 32.
Referring now to
It will be understood that the self-test magnetic field 60b is larger than the self-test magnetic field 60a of
The self-test magnetic field 60b can be a pulsed magnetic field generated by a pulsed current carried by the self-test current conductor 30″. The self-test magnetic field 60b physically adds to any other magnetic field (not shown), e.g., the measured magnetic field, experienced by the magnetic field sensing element 32.
Referring now to
It will be understood that the self-test magnetic field 60c is larger than the self-test magnetic field 60a of
The self-test magnetic field 60c can be a pulsed magnetic field generated by a pulsed current carried by the self-test current conductor 30′″. The self-test magnetic field 60c physically adds to any other magnetic field (not shown), e.g., the measured magnetic field, experienced by the magnetic field sensing element 32.
Referring now to
The self-test magnetic field 60d can be a pulsed magnetic field generated by a pulsed current carried by the self-test current conductor 30″″. The self-test magnetic field 60d physically adds to any other magnetic field (not shown), e.g., the measured magnetic field, experienced by the magnetic field sensing element 32.
Referring now to
The self-test magnetic field 60e can be a pulsed magnetic field generated by a pulsed current carried by the self-test current conductor 30′″″. The self-test magnetic field 60e physically adds to any other magnetic field (not shown), e.g., the measured magnetic field, experienced by the magnetic field sensing elements 32a-32d. In some arrangements, node 62a can be coupled to a power supply voltage, for example, Vcc, node 62d can be coupled to a voltage reference, for example, ground, and nodes 62b, 62c can provide a differential output signal.
Referring now to
The magnetic field sensor 70 can include metal layers 84, 86, 88 separated by insulating layers 76, 78, 80. Other metal and insulating layers (not shown) can be disposed between the conductive layer 76 and the metal layer 84. An electromagnetic shield 72 can be disposed over another insulating layer 74.
Sections 94a-94c are representative of a coil self-test conductor, such as the self-test conductor 30′″ of
Referring now to
Referring now to
The magnetic field sensing element 112 may be disposed on or near the surface 82a of the substrate 82, such as is known for manufacturing of magnetoresistance elements. The magnetic field sensing element 92 can have a maximum response axis 116 generally parallel to the surface 82a of the substrate 82. A self-test current carried by the self-test conductor 114 tends to form a self-test magnetic field along the maximum response axis 116.
Referring now to
A self-test current carried by the self-test conductor 122 tends to form a self-test magnetic field along the maximum response axis 116.
Referring now to
A self-test current carried by the self-test conductor 132 tends to form a self-test magnetic field along the maximum response axis 116.
While
While
Referring now to
Referring now to
Also shown, in some alternate embodiments, the leads can be coupled with a measured conductor 158, which can be formed as a part of the lead frame of which the leads 160a, 160b are another part. A measured current carried by the measured conductor 158 tends to form a magnetic field 162 going into or out of the page, depending upon a direction of the current carried by the measured conductor 158. For these arrangements, the magnetic field sensor 156 can be a current sensor and the magnetic field sensor 156 can instead be responsive to the magnetic field 162 perpendicular to the major surface of the magnetic field sensor 156 (i.e., to the current) rather than to the magnetic field 164.
Referring now to
Referring now to
The diagnostic request processor 190 can also include a pulse generator 198 coupled to receive the decoded diagnostic signal 204a and configured to generate a diagnostic control signal 198a having pulses in response to the decoded diagnostic signal 204a. The diagnostic control signal 198a can be the same as or similar to the diagnostic control signal 58a of
The diagnostic request processor 190 can also include a clock generator 194 configured to generate a periodic clock signal 194a. The diagnostic request processor 190 can also include an internal diagnostic clock generator 196 coupled to receive the clock signal 194a and configured to generate a periodic diagnostic clock signal 196a.
The pulse generator 198 can be coupled to receive the diagnostic clock signal 196a and can be configured to generate the diagnostic control signal 198a having pulses synchronized with the diagnostic clock signal 196a.
Thus, there can be at least two ways to control the pulse generator 198 and associated diagnostics events, i.e., pulses within the diagnostic input signal 198a. As described above, the pulse generator 198 can be responsive to the diagnostic input signal 192. Alternatively, the pulse generator 198 can be responsive to the control signal 196a instead of, or in addition to, the diagnostic input signal 192. When responsive to the control signal 196a, the pulse generator 198 can generate pulses at periodic time intervals, or groups of pulses at periodic time intervals.
The diagnostic request processor 190 can also include a power on circuit 202 coupled to generate power on signal 202a having a first state for a predetermined period of time after the magnetic field sensor, e.g., the magnetic field sensor 10 of
In some embodiments, the diagnostic clock signal 196a has a frequency in the range of about ten Hz to one hundred Hz. However, the diagnostic clock signal 196a can also have a frequency higher than one hundred Hz (e.g., one thousand Hz) or lower than ten Hz (e.g., one Hz) or anywhere in between ten Hz and one hundred Hz.
In some embodiments, the pulse generator 198 generates pulses having a period between about one μs and ten μs in the diagnostic control signal 198a. However, the pulse generator 198 can also generate pulses having a period greater than ten μs (e.g., one hundred μs) or less than one μs (e.g., 0.1 μs) or anywhere in between one μs and ten μs.
The diagnostic control signal 198a can be received by a coil driver circuit 200, for example, a current source, which can be the same as or similar to the coil driver circuit 24 of
Referring now to
The magnetic field sensor 210 can also include a self-test current conductor 224 coupled to receive and carry the self-test current signal 218. While the self-test current conductor 224 is shown to be a coil, from
The magnetic field sensor 210 can also include a magnetic field sensing element 226 proximate to the self-test current conductor 224 such that the magnetic field sensing element 226 can receive a self-test magnetic field generated by the current 218 carried by the self-test current conductor 224. The magnetic field sensing element 226 can also receive a measured magnetic field associated with a magnetic field generator (not shown) that the magnetic field sensor 210 is intended to measure. Thus, the magnetic field sensor is configured to generate a differential composite magnetic field signal 226a, 226b comprising a measured-magnetic-field-responsive signal portion and a self-test-responsive signal portion.
The magnetic field sensor 210 can also include an amplifier 228 coupled to receive the composite magnetic field signal 226a, 226b and configured to generate an amplified signal 228a representative of the composite magnetic field signal 226a, 226b.
The magnetic field sensor 210 can also include a low pass filter 230 and a high pass filter 248, each coupled to receive the amplified signal 228a. The low pass filter 230 is configured to generate a filtered signal 230a and the high pass filter 248 is configured to generate a filtered signal 248a.
A comparator 240 can be coupled to receive the filtered signal 230a. The comparator 240 can have hysteresis or other circuit techniques to result in two thresholds 242, a magnetic field operate point (BOP) and a magnetic field release point (BRP). The BOP and BRP thresholds 242, in some embodiments, can be separated by a voltage equivalent to about five Gauss received by the magnetic field sensing element 226. In other embodiments, the BOP and BRP thresholds 242 can be separated by a voltage equivalent to about fifty Gauss received by the magnetic field sensing element 226. However, the BOP and BRP thresholds 242 can be separated by a voltage equivalent to a magnetic field anywhere between about five and fifty Gauss. The BOP and BRP thresholds 242 can also be separated by a voltage equivalent to a magnetic field smaller than five Gauss or larger than fifty Gauss. The comparator 240 is configured to generate a two state comparison signal 240a.
A comparator 250 can be coupled to receive the filtered signal 248a. The comparator 250 can have hysteresis or other circuit techniques to result in two thresholds, which can be relatively closely spaced about a diagnostic threshold voltage (TH_Diag) 252. In some embodiments, the hysteresis associated with the diagnostic threshold voltage 252 is about fifty millivolts. The comparator 250 is configured to generate a two state comparison signal 250a.
The magnetic field sensor 210 can also include a sensor output formatting circuit (SOFC) 244 coupled to receive the comparison signal 240a and configured to generate a sensor non-linear output signal 244a. The SOFC 244 can be the same as or similar to the sensor output formatting circuit 52 of
The magnetic field sensor 210 can also include a diagnostic output formatting circuit (DOFC) 254 coupled to receive the comparison signal 250a and configured to generate a diagnostic output signal 254a. The DOFC 254 can be the same as or similar to the diagnostic output formatting circuit 56 of
The magnetic field sensor 210 can also include a combining circuit 256 coupled to receive the sensor non-linear output signal 244a, coupled to receive the diagnostic output signal 254a, and configured to generate a combined output signal 256a. The combining circuit 256 can be the same as or similar to the combining circuit 54 of
The magnetic field sensor 210 can also include another SOFC 246 coupled to receive the filtered signal 230a and configured to generate a sensor linear output signal 246a. The SOFC 246 can be the same as or similar to the sensor output formatting circuit 52 of
The magnetic field sensor 210 can also include a diagnostic request processor 260 coupled to receive a diagnostic input signal 258 and configured to generate a diagnostic control signal 260a. The diagnostic request processor 260 can be the same as or similar to the diagnostic request processor 58 or
In operation, upon activation of the diagnostic control signal 260a, the current source 216 can generate one or more current pulses 218, which are carried by the self-test conductor 224 resulting in a self-test magnetic field received by the magnetic field sensing element 226. It will be understood that the self-test magnetic field, and therefore, the self-test-responsive signal portion of the composite magnetic field signal 226a, 226b, can have a frequency content that is generally above a frequency content of a measured magnetic field that the magnetic field sensor 210 is intended to measure. Therefore, the filtered signal 248a can be comprised predominantly of the self-test-responsive signal portion, i.e., pulses, and the filtered signal 230a can be comprised predominantly of the measured-magnetic-field-responsive signal portion. Therefore, by way of the filters 230, 248, the composite magnetic field signal 226a, 226b is split into its two components, the self-test-responsive signal portion and the measured-magnetic-field-responsive signal portion.
In one particular embodiment, the low pass filter 230 has a break frequency of about two hundred kHz and the high pass filter 248 has a break frequency above about two hundred kHz, such that the signal 248a tends to represent the self-test-responsive signal portion of the composite magnetic field signal 226a, 226b. Accordingly, in some embodiments, the measured magnetic field can have a frequency below about two hundred kHz.
It will be understood that the comparator 250 and the diagnostic threshold 252 can assure that the pulses in the filtered signal 248a are of proper and sufficient magnitude to be indicative of proper operation of the magnetic field sensing element 226, amplifier 228, and filter 248. In operation, the comparator 250 generates the two-state comparison signal 250a, i.e., pulses, only when the pulses in the filtered signal 248a are proper. Pulses of the comparison signal 250a can be reformatted into any format by the DOFC 254 to generate the diagnostic output signal 254a. Exemplary formats of the diagnostic output signal 254a are described below in conjunction with
As described above, the filtered signal 230a is predominantly comprised of the measured-magnetic-field-responsive signal portion. The SOFC 246 can reformat the filtered signal 230a into any format to generate the sensor linear output signal 246a. In one particular embodiment, the SOFC 246 merely passes the filtered signal 230a through the SOFC 246, in which case no reformatting occurs.
The comparison signal 240a can be indicative of the magnetic field sensor 210 that operates as a magnetic switch. For example, when the magnetic field sensing element 226 is close to a measured magnetic object, resulting in a magnetic field at the magnetic field sensing element 226 greater than an operating point, the comparison signal 240a has a first state, and when the magnetic field sensing element 226 is not close to the measured magnetic object, resulting in a magnetic field at the magnetic field sensing element 226 less than a release point, the comparison signal 240a has a second different state. The SOFC 244 can reformat the comparison signal 240a into any format to generate the sensor non-linear output 244a. In one particular embodiment, the SOFC 244 merely passes the comparison signal 240a through the SOFC 244, in which case no reformatting occurs.
While many of the blocks of the magnetic field sensor 210 are shown to be analog blocks, it should be appreciated that similar functions can be performed digitally.
Referring now to
The logic circuit 306 can include an AND gate 308 coupled to receive the diagnostic comparison signal 304a, coupled to receive the non-linear sensor comparison signal 240a, and configured to generate a logic signal 308a. The logic signal 308a can be received at a set node of a set/reset flip-flop 310. The set/reset flip-flop 310 can also be coupled to receive the inverted diagnostic control signal 302a at a reset node. The set/reset flip-flop 310 can be configured to generate a control signal 310a received by a p-channel FET 312 acting as a switch to a power supply, Vcc.
The logic circuit 306 can include an inverter 316 coupled to receive the non-linear sensor comparison signal 240a′ and configured to generate an inverted signal 316a. The logic circuit 306 can also include another AND gate 318 coupled to receive the diagnostic comparison signal 304a, coupled to receive the inverted signal 316a, and configured to generate a logic signal 318a. The logic signal 318a can be received at a set node of another set/reset flip-flop 320. The set/reset flip-flop 320 can also be coupled to receive the inverted diagnostic control signal 302a at a reset node. The set/reset flip-flop 320 can be configured to generate a control signal 320a received by an n-channel FET 322 acting as a switch to ground. A source of the FET 312 can be coupled to a drain of the FET 322, forming a junction node. The BOP/BRP thresholds can also be received at the junction node. At the junction node, the sensor output non-linear threshold signal 314 is generated.
With this arrangement, it should be understood that at some times, the sensor output non-linear threshold 314 is equal to BOP, at other times it is equal to BRP, at other times it is equal to Vcc, and at other times it is equal to ground.
Referring briefly to
Referring again to
The addition of the AND gate 304 having an input node coupled to receive the diagnostic control signal 260a results in removal of a possibility that any extraneous spikes or noise pulses in the comparison signal 250a could pass though to the diagnostic output signal 254a when no self-test current pulse 218 is ongoing. Such spikes could result from external magnetic field noise or pulses experienced by the magnetic field sensor 300.
The switch 222 also provides improved function. The switch 222 is only opened when a self-test current pulse 218 is ongoing. The switch is closed at other times. Thus, any external noise or magnetic fields experienced by the magnetic field sensor 300 will not be picked up by the self-test conductor at times when no self-test current pulses 218 are occurring.
Basic operation of the current sensor 300 is described above in conjunction with
Referring now to
In some embodiments, the FETs 354a-354c are within an integrated magnetic field sensor, and the resistors 352a-352c and the power supply, Vdd, are outside of the integrated magnetic field sensor. However, in other embodiments, both the FETs 354a-354c and the resistors 352a-352c are within the integrated current sensor. In still other embodiments, other output circuit arrangements can be used, for example, using bipolar transistors or using a push pull configuration.
Referring now to
The magnetic field sensor 370 also includes a track-and-hold circuit 374 coupled to receive the amplified signal 228a and configured to generate a tracking signal 374a. The track-and-hold circuit 374 is also coupled to receive the diagnostic control signal 260a at a control node such that the track-and-hold circuit holds whenever a current pulse appears in the self-test current signal 218 and tracks otherwise. The magnetic field sensor 370 also includes a differencing circuit 376 coupled to receive the amplified signal 228a, coupled to receive the tracking signal 374a, and configured to generate a difference signal 376a received by the comparator 250 in place of the filtered signal 248a of
In operation, the transparent latch 372 is transparent only when the self-test current signal 218 does not contain a current pulse. Therefore, the latched signal 372a, which is intended to be representative of only the measured-magnetic-field-responsive signal portion of the composite magnetic field signal 226a, 226b is less likely to contain spurious transitions due to the current pulses.
In operation, the tracking signal 374a contains predominantly the measured-magnetic-field-responsive signal portion of the amplified signal 228a, since the track-and-hold circuit holds during the self-test-responsive signal portion of the amplified signal 228a. Thus, the tracking signal 374a is similar to the filtered signal 378a, which is the same as or similar to the filtered signal 230a of
General operation of the magnetic field sensor 370 is similar to that described above in conjunction with
Referring to
The graph 400 includes a sensor non-linear output signal 402 and a sensor linear output signal 408, which can be the same as or similar to the sensor non-linear output signal 244a and the sensor linear output signal 246a of
The sensor linear output signal 408 is shown here as a triangle signal, but can be any linear signal. The sensor linear output signal 408 includes sections with positive slopes, for example, sections 410a, 410b, and sections with negative slopes, for example, a section 412.
The graph 420 includes an exemplary diagnostic control signal 422, which can be the same as or similar to the diagnostic control signal 260a of
The signal 422 can include pulses, of which a pulse 424 is but one example. While the signal 422 is shown to include five pulses, other such signals 422 can include more than five or fewer than five pulses.
The graph 430 includes an exemplary diagnostic input signal 432, which can be the same as or similar to the diagnostic input signal 258 of
While the signal 432 is shown to include five pulses, other such signals 432 can include more than five or fewer than five pulses.
The graph 440 includes another exemplary diagnostic input signal 442, which can be the same as or similar to the diagnostic input signal 258 of
The graph 450 includes yet another exemplary diagnostic input signal 452, which can be the same as or similar to the diagnostic input signal 258 of
The graph 460 includes yet another exemplary diagnostic input signal 462, which can be the same as or similar to the diagnostic input signal 258 of
The graph 470, which has a time scale expanded from that of
The diagnostic input signal 478 can be in one of a variety of formats or protocols, for example, a custom protocol or a conventional protocol, for example, I2C, SENT, BiSS, LIN, or CAN.
It should be understood that each one of the diagnostic input signals 432, 442, 452, 462, and 478 can be decoded by the diagnostic input decoder 204 of
It should be recognized that
Referring now to
The graph 480 includes an exemplary diagnostic input signal 482, which can be the same as or similar to the diagnostic input signal 258 of
The graph 490 includes an exemplary diagnostic control signal 492, which can be the same as or similar to the diagnostic control signal 260a of
The signal 492 can include pulses, of which a pulse 494 is but one example. While the signal 492 is shown to include five pulses, other such signals 492 can include more than five or fewer than five pulses.
Each pulse of the diagnostic input signal 482 can result in one corresponding pulse of the diagnostic control signal 492 and one corresponding pulse of the diagnostic output signal 492. The pulses 494 of the diagnostic output signal 492 are indicative of a self-test that is passing.
While the signal 492 is shown to include five pulses, other such signals 492 can include more than five or fewer than five pulses.
The graph 500 includes yet another exemplary diagnostic output signal 502, which can be the same as or similar to the diagnostic output signal 254a, 254a′ of
The graph 510 includes yet another exemplary diagnostic output signal 512, which can be the same as or similar to the diagnostic output signal 254a, 254a′ of
The graph 520, which has a time scale expanded from that of
The diagnostic output signal 528 can be in one of a variety of formats or protocols, for example, a custom protocol or a conventional protocol, for example, I2C SENT, BiSS, LIN, or CAN.
It should be recognized that
Referring now to
The graph 530, like the graph 400 of
The sensor linear output signal 538 is shown here as a triangle signal, but can be any linear signal. The sensor linear output signal 538 includes sections with positive slopes, for example, sections 540a, 540b, and sections with negative slopes, for example, a section 542.
The graph 550, like the graph 430 of
The graph 560 includes an exemplary combined output signal 562, which can be the same as or similar to the combined output signal 256a, 256a′ of
The graph 570 includes another exemplary combined output signal 572, which can be the same as or similar to the combined output signal 256a, 256a′ of
The graph 580 includes yet another exemplary combined output signal 582, which can be the same as or similar to the combined output signal 256a, 256a′ of
The graph 590 includes yet another exemplary combined output signal 592, which can be the same as or similar to the combined output signal 256a, 256a′ of
Referring now to
The graph 600, like the graph 420 of
The signal 602 can include pulses, of which a pulse 604 is but one example. While the signal 602 is shown to include five pulses, other such signals 422 can include more than five or fewer than five pulses.
The graph 610 includes a sensor non-linear comparison signal 612, which can be the same as or similar to the sensor non-linear comparison signal 240a′ of
The graph 620 includes an exemplary sensor non-linear output signal 622, which can be the same as or similar to the sensor non-linear output signal 244a′ of
Referring now to
The electromagnetic shield 800 can be formed from a metal layer during manufacture of a magnetic field sensor, for example, the magnetic field sensor 70 of
It should be understood that an electromagnetic shield is not the same as a magnetic shield. An electromagnetic shield is intended to block electromagnetic fields. A magnetic shield is intended to block magnetic fields.
In the presence of an AC magnetic field (e.g., a magnetic field surrounding a current carrying conductor), it will be understood that AC eddy currents 812, 814 can be induced in the electromagnetic shield 800. The eddy currents 812, 814 form into closed loops as shown. The closed loop eddy currents 812, 814 tend to result in a smaller magnetic field in proximity to the electromagnetic shield 800 than the magnetic field that induced the eddy currents 812, 814. Therefore, if the electromagnetic shield 800 were placed near a magnetic field sensing element, for example, the magnetic field sensing element 92 of
The slit 806 tends to reduce a size (i.e., a diameter or path length) of the closed loops in which the eddy currents 812, 814 travel. It will be understood that the reduced size of the closed loops in which the eddy currents 812, 814 travel results in smaller eddy currents 812, 814 and a smaller local effect on the AC magnetic field that induced the eddy current. Therefore, the sensitivity of a magnetic field sensor on which the magnetic field sensing element 816 and the electromagnetic shield 800 are used is less affected by the smaller eddy currents.
Furthermore, by placing the shield 800 in relation to the magnetic field sensing element 816 as shown, so that the slit 806 passes over the magnetic field sensing element 816, it will be understood that the magnetic field associated with any one of the eddy currents 812, 814 tends to form magnetic fields passing through the magnetic field sensing element 816 in two directions, canceling over at least a portion of the area of the magnetic field sensing element 816.
Referring now to
In the presence of a magnetic field, it will be understood that eddy currents 868-874 can be induced in the electromagnetic shield 850. Due to the four slits 860-866, it will be understood that a size (i.e., a diameter or a path length) of the closed loops eddy currents 866-874 tends to be smaller than the size of the closed loop eddy currents 812, 814 of
Furthermore, by placing the shield 850 in relation to the magnetic field sensing element 880 as shown, so that the slits 860-866 pass over the magnetic field sensing element 880, it will be understood that the magnetic field associated with any one of the eddy currents 868-874, tends to form magnetic fields passing through the magnetic field sensing element 880 in two directions, canceling over at least a portion of the area of the magnetic field sensing element 880.
Referring now to
It will be recognized that the electromagnetic shield 900 is able to support eddy currents having a much smaller size (i.e., diameter of path length) than the electromagnetic shield 850 of
Referring now to
While shields having features to reduce eddy currents are described above, the shield 72 of
Referring now to
The gearshift lever 1000 can have a magnet 1002 disposed on an end thereof nearest to the magnetic field sensors 1004a-1004f. In operation, a magnetic field sensor, e.g., the magnetic field sensor 1004d, senses when the gearshift lever 1000 is at a position of the particular magnetic field sensor, e.g., 1004d, and thus, senses the particular gear associated with the position of the gear shift lever. In this way, the magnetic field sensors 1004a-1004f can provide respective signals to a computer processor or the like, which can electronically/mechanically configure the automobile transmission into the selected gear.
This particular arrangement is shown to point out a potential problem with the arrangements of
In some embodiments, this shortcoming can be overcome merely by selecting the magnetic field generated by the magnet 1002 to be in a direction opposite to the direction of the magnetic field generated by the self-test conductor 224. However, in other embodiments, it may be desirable to have a magnetic field sensor that can select and/or change a direction of the magnetic field generated by the self-test conductor 224. An exemplary arrangement having this ability is shown in
Referring now to
Two comparators 1010, 1012 can be coupled to receive the signal 228a from the amplifier 228. The comparator 1010 can also be coupled to receive a comparison signal 1014a representative of a signal from the amplifier 228 when the magnetic field sensing element experiences zero Gauss (or a background magnetic field, e.g., the earth's magnetic field) plus a delta. The comparator 1012 can also be coupled to receive a comparison signal 1014b representative of a signal from the amplifier 228 when the magnetic field sensing element experiences zero Gauss (or a background magnetic field, e.g., the earth's magnetic field) minus a delta.
The comparator 1010 can generate a first comparison signal 1010a, and the comparator 1012 can generate a second comparison signal 1012a.
A flip-flop (i.e., a latch) 1020 can be coupled to receive the first and second comparison signals 1010a, 1012a, respectively at set and reset inputs and can be configured to generate a first output signal 1020a and a second output signal 1020b.
A first logic gate, for example, an AND gate 1022, can be coupled to receive the first output signal 1020a, coupled to receive the diagnostic control signal 260a (
A second logic gate, for example, an AND gate 1024, can be coupled to receive the second output signal 1020b, coupled to receive the diagnostic control signal 260a, and configured to generate a control signal 1024a (Control B).
The self-test conductor 224 can be arranged in the cross arm of an H-bridge surrounded by switches 1026a, 1026b, 1028a, 1028b. The switches 1026a, 1026b are controlled by the first control signal 1022a, and the switches 1028a, 1028b are controlled by the second control signal 1024a.
Thus, in operation, when the current generator 216 generates the current 218 in response to the diagnostic control signal 260a, the current 218 flows through the self-test conductor 224 in one of two directions determined by the first and second control signals 1022a, 1024a.
The comparators 1010, 1012 and the flip flop 1020 operate essentially as a window comparator, so that when the magnetic field experienced by the magnetic field sensing element 226 is large in a first direction, the diagnostic current passing through the self-test conductor 224 generates a magnetic field in an opposite second direction (when the diagnostic control signal 260a is also high). Conversely, when the magnetic field experienced by the magnetic field sensing element 226 is large in the second direction, the diagnostic current passing through the self-test conductor 224 is in the opposite first direction (when the diagnostic control signal 260a is also high).
With this arrangement, even in the presence of a fairly large magnetic field in either direction, which tends to saturate the magnetic field sensing element 226, or electronics coupled to the magnetic field sensing element, for example, the amplifier 228, still the self-test signal 218 can generate a magnetic field in the opposite direction, which can propagate to the diagnostic output signal 254, 254a′ of
It will be apparent that the circuit of
All references cited herein are hereby incorporated herein by reference in their entirety. Having described preferred embodiments of the invention, it will now become apparent to one of ordinary skill in the art that other embodiments incorporating their concepts may be used. It is felt therefore that these embodiments should not be limited to disclosed embodiments, but rather should be limited only by the spirit and scope of the appended claims.
This application is a Continuation Application of U.S. patent application Ser. No. 12/706,318, filed Feb. 16, 2010, now U.S. Pat. No. 8,447,556, which application claims the benefit under 35 U.S.C. §119(e) U.S. Provisional Application No. 61/153,059 filed Feb. 17, 2009, which applications are incorporated herein by reference in their entirety.
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| Number | Date | Country | |
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| Number | Date | Country | |
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| 61153059 | Feb 2009 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12706318 | Feb 2010 | US |
| Child | 13743451 | US |
