Abstract:
A closed-loop calibration scheme is configured to allow a device to remain in continuous operation. A signal generator device provides a pseudorandom sequence for a signal received by a magnetic field magnetic field sensor, such as a Hall-effect sensor. A signal decoder circuit receives the output signal and decouples the generated spread spectrum signal from the interference by measuring the gain in the overall signal. The decoder device distinguishes the known spread spectrum signal from any perturbation effects of particular bandwidths. A processing circuit then outputs a signal that has an operation parameter that has been adjusted to compensate for the perturbation effects. The processing circuit provides the receiver circuit with the compensation signal, hence forming a closed-loop calibration configuration.

Description:
RELATED APPLICATION(S) 
       [0001]    This application claims the benefit of U.S. provisional patent application number 62/273,033 filed Dec. 30, 2015, the contents of which are incorporated by reference as if fully rewritten herein. 
     
    
     TECHNICAL FIELD 
       [0002]    This invention relates generally to calibration of devices and, in particular, to using application of a signal to a device to derive feedback information for the device&#39;s operation such as closed-loop calibration of a Hall-effect sensor. 
       BACKGROUND 
       [0003]    Open and closed loop calibration methods are generally known and applied in a variety of contexts. One such context is in the calibration of Hall-effect magnetic field sensors. Hall-effect magnetic field sensors are solid state magnetic sensor devices that can be used to measure magnetic fields. Applications of Hall-effect magnetic field sensors require high accuracy; however, they are known to suffer from variation and drift in sensitivity with process variations, temperature, and package stress changes. The conventional solution to control for the complex temperature dependence that Hall-effect sensors exhibit is to implement so-called “open-loop” temperature compensation circuitry configurations. Fine-tuning (or “trimming”) the sensitivity of each part for the process variation may be carried out, and the changes in sensitivity with temperature and stress may be compensated for by using on-chip temperature and stress sensors and pre-evaluated compensation tables. This approach requires expensive multi-point characterization of individual devices and re-calibration over time. The magnetic field excitation for calibration of the sensor can be created using an on-chip current coil or external magnetic field sources. Calibration, however, can only be performed when the device is offline and hence, not in operation, as the signal to be measured can interfere with the calibration signal. 
         [0004]    As an alternative to the open-loop scheme, closed-loop methods have been implemented to perform continuous calibration in the absence of external magnetic fields. Closed-loop calibration typically works as follows: a known magnetic field is applied to the device (a method of generating known magnetic field would be: a known temperature-insensitive current is passed through an on-chip/off-chip coil/other suitable trace near the sensor), the sensor output is then compared with the desired response, and the sensor sensitivity/gain is adjusted to minimize the comparator error. This results in much higher accuracy than the open-loop configuration. 
         [0005]    A known issue with conventional closed-loop calibration of a Hall-effect sensor is that the calibration current near the Hall-effect sensor can generate enough heat that it changes the operating temperature, resulting in a change of sensitivity and affecting the primary measurement. Additionally, closed-loop calibrations have been demonstrated to perform well in the absence of external magnetic fields, but completely eliminating interference in real-world applications is non-trivial and can require offline calibration in a magnetically shielded environment. 
       SUMMARY 
       [0006]    Generally speaking, pursuant to these various embodiments, a closed-loop calibration scheme may be configured in such a manner for a device to remain in continuous operation (i.e., online). In one particular example, a signal generator device is configured to provide a pseudorandom sequence spreading the signal over a wide range of frequencies. This “spread spectrum” signal is received by a magnetic field generator, which provides an encoded or “spread spectrum” magnetic field signal to a magnetic field sensor, such as a Hall-effect sensor. External interference of particular bandwidths can influence the overall sensor output signal. A signal decoder circuit receives the output signal, however, and can decouple the generated spread spectrum signal from the interference by using an appropriate decoding scheme on the overall received signal. By definition, the spread spectrum signal is spread over the frequency domain, so the decoder device acts to distinguish the known spread spectrum signal from any interference of particular bandwidths. The output corresponding to the spread spectrum signal, however, is dependent on any perturbation effect that changes the sensitivity of the magnetic sensor. A processing circuit can then output a signal that has an operation parameter that can be adjusted to compensate for said perturbation effects. The processing circuit provides the receiver circuit with the compensation signal, hence forming a closed-loop calibration configuration. 
         [0007]    This scheme enables the use of a small calibration signal (current) avoiding the previously presented problem of heat generation near the Hall-effect sensor, thereby maintaining the operating temperature. Such a configuration allows for continuous calibration, eliminating the need for expensive multi-point temperature testing. Furthermore, the device is thus able to continually remain in operation 
         [0008]    These and other benefits may become clearer upon making a thorough review and study of the following detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a block diagram of an example device with a closed-loop calibration configuration in accordance with various embodiments of the invention. 
           [0010]      FIG. 2  is a block diagram of another example device with a closed-loop calibration further configured to consist of a spread spectrum signal and decoder circuit in accordance with various embodiments of the invention. 
           [0011]      FIG. 3  is circuit diagram of an example device similar to  FIG. 2 , further including a Hall-effect sensor and additional circuitry elements in accordance with various embodiments of the invention. 
           [0012]      FIG. 4  is a flow chart illustrating a method of operation in accordance with various embodiments of the invention. 
           [0013]    Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and/or relative positioning of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments. It will further be appreciated that certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. It will also be understood that the terms and expressions used herein have the ordinary technical meaning as is accorded to such terms and expressions by persons skilled in the technical field as set forth above except where different specific meanings have otherwise been set forth herein. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Referring now to the drawings, and in particular to  FIG. 1 , a simplified closed-loop calibration circuitry device example  140  is shown. In this configuration, a signal generator device  141  provides a pseudorandom wideband calibration signal  142 , wherein a nearly random sequence of bits (e.g., ones and zeros) is spread over a wide range of frequencies. A receiver circuit device  143  then receives the calibration signal  142  and outputs a new signal  144  that is at least dependent on said wideband calibration signal  142 , any input signal  130  that the device is supposed to measure, as well as other possible perturbation effects  145  that changes the response/characteristics of the receiver  143  such as temperature effects. A processing circuit  146  receives the output signal  144  and a desired response signal  147 . In this manner, the processing circuit  146  may determine what compensation signal  148  should then be applied back to the receiver circuit device  143 . The compensation signal  148  effects adjustment of an operation parameter thereby countering said perturbation effects  145  based on a comparison of at least an aspect of the output  144  based on the pseudorandom wideband calibration signal  142  and the desired response signal  147 . The receiver circuit device  143  receives said compensation signal  142 , thereby forming a closed-loop calibration configuration, and the device  140  can remain in continuous operation. Separately, a de-embedding circuit  160  provides a detected output  170  that includes only the aspects of the input signal  130  while removing the effects of the pseudorandom wideband calibration signal. 
         [0015]    Generally speaking, the receiver circuit device  143  can be any device that receives outside signals and provides an output that is dependent on the received outside signals. Examples include magnetic field detectors such as a Hall-effect sensor, magneto-resistive sensor (XMR) like anisotropic magneto-resistive (AMR), giant magneto-resistive (GMR), tunneling magneto-resistive (TMR), colossal magneto-resistive (CMR), fluxgate sensor etc. The approaches described herein are further applicable to other types of sensors such as infrared sensors, photosensors, audio sensors, ultrasound sensors, and the like. In the example where the receiver circuit device  143  is a magnetic field detector, the de-embedding circuit  160  effectively separates out from the output signal  144  aspects due to the calibration signal  142  such that the de-embedding circuit  160  can then provide a detected output that accurately depicts the otherwise sensed magnetic field. 
         [0016]    In another approach illustrated in  FIG. 2 , the device is configured in such a manner that the signal generator  241  is further comprised of a spread spectrum signal. The spread spectrum technique takes a generated signal of a particular bandwidth (the pseudorandom wideband calibration signal  242  in this embodiment) and expands it in the frequency domain. The encoded spread spectrum signal is known to resist interference and hence may remain distinguishable from any perturbation effects  245 . 
         [0017]    A receiver circuit  243  is configured to receive the pseudorandom wideband calibration signal  242 , which now comprises a spread spectrum signal  251 . A (spread spectrum) decoder circuit  250  then receives the output signal  244  from the receiver circuit  243  that is comprised of the pseudorandom wideband calibration signal  242  as well as any input signal  230  sensed by the receiver circuit  243 . The response or transfer function of the receiver is also affected by any additional perturbation  245 . The decoder circuit  250  detects the spread spectrum signal and, in turn, separates the known pseudorandom wideband calibration signal  242  from the input signal  230 . This decoded signal  249  is sent to the processing circuit  246  that may then compare the decoded signal  249  to the desired response signal  247 . A compensation signal  248  may now be sent from the processing circuit  246  back to the receiver circuit  243 , thus forming a closed-loop configuration, and allowing for an highly accurate, iterative process. Separately, the de-embedding circuit  260  provides a detected output  270  that includes aspects of the output not based on the pseudorandom wideband calibration signal, but only based on the input signal  230  detected by the receiver circuit  243 . 
         [0018]      FIG. 3  illustrates another example of a closed-loop calibration apparatus. In this configuration, the signal generator circuit is a pseudorandom bit sequence (“PRBS”) signal generator  341 . The PRBS generator  341  provides a signal to generate a magnetic field of known frequency to be supplied to the receiver circuit device that, in this example, is a magnetic field detector  343 . A reference current generator  351  provides current to a coil  352  to create the calibration magnetic field for the magnetic field detector  343  such that it receives the magnetic field that changes with the pseudorandom wideband calibration signal. The H-bridge-like switch combination  344  is the modulator that changes the direction of current through the coil  352  depending on the PRBS electrical signal to facilitate provision of a PRBS magnetic signal. The PRBS magnetic field signal is received by a Hall-effect sensor  353 , which may be a nearby the coil  352 . A Hall-effect sensor frontend circuit  354  receives the generated magnetic field current from the Hall-effect sensor  353  and interfaces with the decoder circuit  350 . 
         [0019]    Generally speaking, the decoder circuit  350  allows for discrete time signal processing of the output from the sensor. In this example, the decoder circuit  350  receives the output from the Hall-effect sensor frontend circuit  354  and the pseudorandom wideband calibration signal and provides the aspect of the output based on the pseudorandom wideband calibration signal for comparison to the desired device response signal. As illustrated in  FIG. 3 , this circuit includes the switched capacitor demodulator  364 , SC integrator circuit  363 , and a sample and hold circuit  365 . The SC demodulator  364  is configured to receive the output from the receiver circuit device  343  and the pseudo random bit sequence generated by the PRBS generator  341  and generates a demodulated signal. The SC integrator  363  receives the demodulated signal and a clock signal provided by a clock  342  for the pseudorandom wideband calibration signal to create an integrated signal. The SC integrator circuit  363  derives the aspect of the output based on the pseudorandom wideband calibration signal and integrates the aspect of the output based on the pseudorandom wideband calibration signal over a time period to provide an integrated output. The integrated output is stored in the sample and hold circuit  365  for the entire length of the PRBS sequence until the next integrated signal. The stored signal is used for comparison to the desired device response signal. 
         [0020]    More specifically, in this example of  FIG. 3 , a differential signaling is used. The PRBS signal S  360  and its inverse Sbar  361  are used as a modulating signal for the PRBS modulator  344 . The output from the receiver circuit device  343  is also a differential signal, which is demodulated using the PRBS signal S and Sbar. 
         [0021]    The processing circuit  346  further includes an error circuit  358 . The error circuit  358  includes an error amplifier  357  configured to receive the desired device response signal  347  and the integrated output from the sample and hold circuit  365 . The error amplifier  357  outputs an error signal through comparison between the received signals. A loop stabilizing switched capacitor integrator circuit  359  is configured to receive the error signal and to provide the compensation signal based on the error signal. The compensation signal is routed as feedback to the Hall bias current generator  348  to help control the Hall effect sensor  353 . 
         [0022]    The processing circuit  346  also includes a calibration signal cancellation/de-embedding circuit  375  configured to receive the output from the Hall-effect sensor frontend circuit  354  and the pseudorandom wideband calibration signal. The calibration signal cancellation circuit  375  provides a clean output signal removing effects of application of the pseudorandom wideband calibration signal to the Hall Effect sensor  353 . 
         [0023]    An example method of operation in accord with these disclosures is illustrated in  FIG. 4 . The method includes applying a pseudorandom wideband calibration signal generated by a signal generator to a receiving device  400 ; an example of a generated pseudorandom wideband calibration signal is a spread spectrum signal  400   a . This application can be effected using an integrated or nearby coil disposed with the device, for example, in the case where the device is a Hall-effect sensor, which detects  401  the applied magnetic field that changes with the pseudorandom wideband calibration signal together with other magnetic fields that engage the device. Accordingly, the receiver device provides  402  an output dependent on at least the pseudorandom wideband calibration signal and perturbation effects as well as the other sensed signals (e.g., magnetic fields). 
         [0024]    The output signal is then decoded  403  by a decoder circuit that disentangles the known pseudorandom wideband calibration signal from the other sensed signals but while retaining the effect of the external perturbations. The decoded signal is received  404  by a processing circuit and compared to a desired device response signal to create  405  a compensation signal. 
         [0025]    The creation and provision  405  of the compensation signal can be performed in any number of ways including those described above. By one approach, this step can be performed by receiving the output and the pseudorandom wideband calibration signal by a decoder circuit and providing by the decoder circuit the aspect of the output based on the pseudorandom wideband calibration signal for comparison to the desired device response signal. 
         [0026]    In one particular implementation of the method, for instance as performed by the circuit of  FIG. 3 , a demodulator circuit receives the output and the pseudorandom wideband calibration signal. The aspect of the output based on the pseudorandom wideband calibration signal is derived and integrated over a time period to provide an integrated output. The integrated output is provided to a sample and hold circuit configured to receive and store for comparison to the desired device response signal. An error amplifier receives the desired device response signal in an error amplifier and the integrated output from the sample and hold circuit. The error amplifier outputs an error signal received by a loop stabilizing switched capacitor integrator circuit, which in turn provides the compensation signal based on the error signal. The compensation signal is used to adjust  406  an operation parameter to counter the perturbation effects for the device based on a comparison of an aspect of the output based on the pseudorandom wideband calibration signal and the desired device response signal. Now the configuration of the device can form a closed loop as the receiver circuit is provided with signal that compensates for the perturbation effects. 
         [0027]    So configured, the closed loop approach allows for fine-tuning of the sensor device without having to remove outside influences from the sensor. In the Hall-Effect example, there is no need to shield the Hall-Effect sensor from outside magnetic fields to adjust its parameters. Similarly, perturbation effects based on temperature or on-chip environmental factors can be addressed on the fly. 
         [0028]    Those skilled in the art will recognize that a wide variety of modifications, alterations, and combinations can be made with respect to the above described embodiments without departing from the scope of the invention, and that such modifications, alterations, and combinations are to be viewed as being within the ambit of the inventive concept.