Integrated electronic device including a full scale adjustment stage for signals supplied by a MEMS sensor
10921164 ยท 2021-02-16
Assignee
Inventors
Cpc classification
B81B7/008
PERFORMING OPERATIONS; TRANSPORTING
International classification
Abstract
A MEMS sensor generates an output multiscale reading signal supplied to a full scale adjustment stage. The full scale adjustment stage includes a signal input configured to receive the reading signal, a saturation assessment block, and a full scale change block. The saturation assessment block is coupled to the signal input and configured to generate a scale increase request signal upon detection of a saturation condition. The full scale change block is coupled to the saturation assessment block and configured to generate a full scale change signal upon reception of the scale increase request signal.
Claims
1. An electronic device, comprising: a signal input configured to receive a reading signal produced by a MEMS sensor device that is subject to saturation; and circuitry coupled to the signal input and configured to: generate a saturation detection signal based on the reading signal produced by the MEMS sensor device; generate a saturation prediction signal that predicts when saturation will occur based on the reading signal produced by the MEMS sensor device; and generate a full scale change signal based on the saturation detection signal and the saturation prediction signal, wherein the full scale change signal, in operation, is provided to the MEMS sensor device and directs the MEMS sensor device to adjust its full scale in accordance with the full scale change signal.
2. The electronic device according to claim 1, wherein the circuitry comprises: a saturation detector.
3. The electronic device according to claim 2, wherein the saturation detector comprises: a comparator configured to compare the reading signal with at least one saturation threshold value and further configured to generate the saturation detection signal based on the comparison of the reading signal with the at least one saturation threshold value.
4. The electronic device according to claim 1, wherein the circuitry comprises: a saturation predictor configured to generate the saturation prediction signal.
5. The electronic device according to claim 4, wherein the saturation predictor is configured to generate a normalized signal sample; store a previous normalized signal sample; generate a predicted signal sample based on the normalized signal sample and the previous normalized signal sample; and generate the saturation prediction signal if the predicted signal sample exceeds at least one normalization limit threshold.
6. The electronic device according to claim 1 wherein the circuitry is configured to: compare the reading signal with a decrease threshold; and generate a scale-decrease request signal based at least in part on the comparison of the reading signal with the decrease threshold.
7. The electronic device according to claim 6, wherein the circuitry is configured to: generate a full scale decrease request signal upon reception of a threshold number of scale decrease request signals.
8. The electronic device according to claim 6, wherein the circuitry is configured to: generate a first scale increase request signal upon reception of a threshold number of saturation prediction signals.
9. The electronic device according to claim 8, wherein the circuitry is configured to: generate a second scale increase request signal upon reception of a threshold number of saturation detection signals.
10. The electronic device according to claim 9, wherein the circuitry is configured to generate a full scale increase signal when the scale-decrease request signal and at least one of the first scale increase signal and the second scale increase signal is received.
11. The electronic device according to claim 1, wherein the circuitry is configured to: output a replacement signal sample when a saturation condition of the reading signal is determined.
12. The electronic device according to claim 11, wherein the circuitry is configured to: store a previous normalized signal sample; and generate the replacement signal sample based on a normalized signal sample and the previous normalized signal sample.
13. The electronic device according to claim 11, wherein the circuitry is configured to: store a normalized signal sample; and use interpolation to generate the replacement signal sample based on the normalized signal sample and the previous normalized signal sample.
14. The electronic device according to claim 11, wherein the circuitry is configured to: amplify the replacement signal sample.
15. The electronic device according to claim 14, wherein the circuitry is configured to select the reading signal or the replacement signal sample.
16. The electronic device according to claim 1, wherein the reading signal is a digital signal and the circuitry is configured to process digital signals.
17. A sensing system, comprising: a MEMS sensor having an input arranged to receive a full scale change signal and an output, wherein the MEMS sensor is arranged to adjust its full scale in accordance with the full scale change signal; and signal processing circuitry coupled to the input and the output of the MEMS sensor and configured to: generate an analog reading signal; generate a digital reading signal based on the analog reading signal; generate a saturation detection signal based on the digital reading signal; generate a saturation prediction signal that predicts when saturation will occur based on at least one of the analog reading signal and the digital reading signal; and generate the full scale change signal based on the saturation detection signal and the saturation prediction signal.
18. The sensing system according to claim 17, wherein the MEMS sensor element and a first portion of the circuitry are formed in a first integrated circuit and a second portion of the circuitry is formed in a second integrated circuit.
19. The sensing system according to claim 17, wherein the circuitry is configured to: generate a replacement signal sample when a saturation condition of the digital reading signal is determined.
20. The sensing system according to claim 19, wherein the circuitry is configured to: generate an amplified signal.
21. A sensing system method, comprising: producing a digitized reading signal with a MEMS sensor device; and providing an amplified reading signal based on a full scale adjustment of the digitized reading signal, the full scale adjustment including: generating a saturation detection signal based on the digitized reading signal; generating a saturation prediction signal that predicts when saturation will occur based on the digitized reading signal; generating a replacement control signal based on a saturation assessment of the digitized reading signal, the saturation assessment being based on the saturation detection signal and the saturation prediction signal; applying the replacement control signal to select either a replacement signal or the digitized reading signal for amplification; converting the selected one of the replacement signal and the digitized reading signal into the amplified reading signal; and feeding a full scale adjustment signal back to the MEMS sensor device, wherein the MEMS sensor device is arranged to adjust its full scale in accordance with the full scale change signal.
22. The sensing system method according to claim 21, wherein generating the replacement control signal comprises: detecting when the digitized reading signal is outside of at least one saturation threshold value; and producing, based on the detecting, the saturation detection signal.
23. The sensing system method according to claim 22, wherein generating the replacement control signal comprises: normalizing the digitized reading signal to produce a normalized signal; storing the normalized signal in a memory; generating a predicted value based on the normalized signal and a previous normalized signal; and comparing the predicted value to at least one normalization limit threshold; and based on the comparison of the predicted value to the at least one normalization limit threshold, producing the saturation prediction signal.
24. The sensing system method according to claim 22, wherein generating the replacement control signal comprises: when the saturation prediction signal indicates saturation is predicted, producing a scale increase request based on the saturation detection signal and the saturation prediction signal; when the saturation prediction signal does not indicate saturation is predicted, producing the scale increase request based on the saturation detection signal; comparing the digitized reading signal to a full-scale threshold value; based on the comparison of the digitized reading signal to the full-scale threshold value, producing a scale decrease request; and logically combining the scale increase request and the scale decrease request to produce the replacement control signal.
Description
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
(1) Non-limiting and non-exhaustive embodiments are described with reference to the following drawings, wherein like labels refer to like parts throughout the various views unless otherwise specified. For a better understanding of the present disclosure, embodiments thereof are now described, purely by way of non-limiting example, with reference to the attached drawings, wherein:
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DETAILED DESCRIPTION
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(9) The sensing system 50 further comprises a reading stage 52, similar to the corresponding stage 11 of
(10) The full scale adjustment stage 54, which may be integrated in an own chip or integrated with the reading stage 52, the ADC stage 53 and/or the DSP stage 55, has the purpose of automatically detecting when a full scale change is to be carried out and generate appropriate control signals for the reading stage 52. In particular, the full scale adjustment stage 54 may operate by detecting saturation of the signal outputted by the ADC stage 53 and possibly intervening for changing the full scale. The full scale adjustment stage 54 may also comprise a mode for predicting the possibility of saturation and changing the full scale, so as to change the full scale in advance in order to prevent saturation and/or to check advisability of reducing the used full scale for improving the sensitivity of the sensing system.
(11) The full scale adjustment stage 54 described hereinafter operates downstream of the ADC 53, on samples of the digitized reading signal S1 supplied by the ADC. Consequently, according to the context, hereinafter reference will be made indifferently to the digitized reading signal or to the samples thereof, which are both designated by S1, as for the signals processed by the full scale adjustment stage 54.
(12) In detail, the full scale adjustment stage 54 comprises a saturation detector/predictor block 60; a sample replacement block 61; a decision block 62; and an alignment block 63.
(13) The saturation detector/predictor block 60 has an input connected to the ADC stage 53, from which it receives the samples of the digitized reading signal S1, and outputs a saturation detection signal O.sub.D and a saturation prediction signal O.sub.P supplied to the decision block 62.
(14) The saturation detector/predictor block 60 has the aim of warning and triggering the decision block 62 when it detects (on a current sample) or predicts (on a subsequent sample) saturation of the digitized reading signal S1.
(15) The sample replacement block 61 is connected at its input to the ADC stage 53, from which it receives the samples of the digitized reading signal S1, and outputs replacement samples S2 of a value such as to reduce the error with respect to an (ideal) non-saturated output. The output of the sample replacement block 61 is coupled to the alignment block 63 as well as, optionally, to the saturation detector/predictor block 60.
(16) The decision block 62 performs multiple functions, among which deciding when to change the full scale value and coordinating the other blocks 60, 61, 63. The decision block 62 connected to the ADC stage 53, from which it receives the samples of the digitized reading signal S1, and to the saturation detector/predictor block 60, from which it receives the detection and prediction saturation signals O.sub.D and O.sub.P. The decision block 62 outputs a plurality of signals, among which: a current full scale signal s.sub.FS supplied to the sensor element 51, to the reading stage 52, to the saturation detector/predictor block 60, to the sample replacement block 61, and to the alignment block 63; a replacement control signal s.sub.S supplied to the alignment block 63, to the sample replacement block 61, and to the saturation detector/predictor block 60; and dithering signals s.sub.D supplied to the dithering blocks 57, 58, if provided, as described in greater detail hereinafter.
(17) Specifically, the saturation detector/predictor block 60 may comprise a saturation detector element 70 and a saturation predictor element 71, both receiving the samples of the digitized reading signal S1 and outputting, respectively, the saturation detection signal O.sub.D and the saturation prediction signal O.sub.P. As an alternative, in simpler applications, the saturation detector/predictor block 60 may comprise just the saturation detector element 70.
(18) When the saturation detector/predictor block 60 has a complete structure, it attempts to predict when a subsequent sample of the digitized reading signal S1 may saturate in order to set an increase of the full scale such as to prevent likely saturation. If, however, it is not possible to prevent saturation (for example, owing to an estimation error, or because the signal detected by the sensor element 50 switches too fast) and the digitized reading signal S1 saturates, the saturation detector element 70 intervenes, issuing a warning that it is precisely the current sample that is the result of the saturation. Consequently, as explained in greater detail with reference to
(19) The saturation detector element 70 may be implemented via a simple comparator 73 that detects whether the digitized reading signal S1 is equal to one of the two extreme values TH1, TH2 of the sequence of bits that encodes the samples of the digitized reading signal S1, as shown in
(20) Alternatively, it is possible to set a margin with respect to the extreme values indicated above for generating the logic saturation condition of the saturation detection signal O.sub.D even when the digitized reading sample S1 is only close to one of the extremes without, however, having reached it. In this situation, in fact, even a minor further displacement of the digitized reading signal S1 towards the extreme could cause saturation of the output of the ADC stage 53, thus increasing the likelihood of saturation occurring on the next sample. This is represented graphically in
(21) The saturation predictor element 71 has the purpose of predicting whether the next sample of the digitized reading signal S1 will be saturated. To do this, it bases its operation on the past samples (stored in a suitable memory) and on the current sample of the digitized reading signal S1. Since each sample may be generated with a scale different from the other (past or future) samples, because of the change of scale, in order to be able to make the calculations, a normalization stage is provided that renders the data homogeneous.
(22) The saturation predictor element 71 may thus have the structure shown in
(23) The memory 76 further receives the replacement sample S2 from the sample replacement block 61 and is connected at the output to the prediction processing unit 77.
(24) The prediction processing unit 77 thus generates a predicted value x.sub.P, in the way described in greater detail hereinafter.
(25) The predicted value x.sub.P is supplied to a comparator 78, which compares it with two limit values TH3 and TH4 representing the extreme values of the dynamics referred to at the current scale or values that include a margin threshold, which may be different from that of the saturation detector element 70. On the basis of the outcome of the comparison, according to whether the predicted value x.sub.P is lower or higher than the threshold provided, the comparator 78 generates a corresponding logic value of the saturation prediction signal O.sub.P.
(26) The sample memory 76 may, for example, be a shift register, a FIFO (First-In-First-Out) memory or the like, provided with a plurality of outputs for always outputting the n most recent samples.
(27) The prediction processing unit 77 may be implemented according to any of the many prediction methods and algorithms known in literature.
(28) For example, a first order predictor could be used, which represents an excellent compromise between area, complexity, and effectiveness. As is known, this predictor computes the addition between the current sample and the difference between the last two samples, according to the following Eq. (1):
x[n+1].sub.P=x[n]+(x[n]x[n1])=2x[n]x[n1](1)
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(30) In particular, if the sample replacement block 61 is implemented as a predictor (
(31) In this case, advantageously, the replacement sample S2 is already ready to be used since only the previous samples are considered to generate it, and thus the sample replacement block 61A does not introduce any delays. However, in some situations, this solution may generate samples that considerably depart from the ideal ones so that, according to the requirements, connection of the output of the first replacement processing unit 82 to the first sample memory 81 may be omitted.
(32) If the sample replacement block 61 is implemented as an interpolator (
(33) The sample replacement block 61B of
(34) The second replacement processing unit 88 may have various architectures and implementations. By way of example, a linear interpolator may be used, characterized by the following Eq. (2):
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(36) This leads to a more precise estimation, also because, for the subsequent samples, the full scale change has already occurred by virtue of the saturation detector/predictor block 60; thus, these samples are no longer obtained in a saturation condition.
(37) The solution of
(38) In all the solutions of
(39) If saturation occurs, it may be useful for both the sample replacement block 61 and the saturation predictor element 71, if present, not to store the sample of the reading signal S1, which is by now saturated, but the replacement sample S2, in order to generate sufficiently accurate subsequent estimates. Consequently, the output of the sample replacement block 61 is connected to the sample memories 76 and 81 or 87 of
(40) The decision block 62 may predict a non-immediate change of full scale and, in this case, may comprise counters and registers to store the requests of change of full scale and the parameters that may affect the decision of increasing or decreasing the full scale.
(41) To this end, the decision block 62 may have the architecture shown in
(42) The scale change-decision block 62 of
(43) In detail, the decision block 62 comprises a decrease comparator 90, a decrease counter 91, a first increase comparator 92, a second increase comparator 94, an OR gate 95, and a logic stage 93 for full scale change decision. The logic stage 93 may comprise, for example, a logic unit 98 and a memory (such as a look-up table) 99.
(44) The decrease comparator 90 receives the sample of the digitized reading signal S1 from the ADC block 53 and compares it with a threshold value TH5 that is preset or set by the user. For example, the threshold value TH5 may be a value close to zero (taking into account the sign); i.e., it may be close to half of the full scale value in the digitization used, as represented in
(45) The decrease counter 91 increments its value as it receives each low-sample signal s.sub.LS and generates a scale-decrease request s.sub.DW for the logic stage 93 when it receives a given number of low-sample signals s.sub.LS, for example three or four.
(46) The first increase comparator 92 receives the saturation prediction signal O.sub.P (in general, one bit) and counts it, supplying a prediction scale increase request signal s.sub.UP_P upon detection of a given number of saturation prediction signals O.sub.P. The second increase comparator 94 receives the saturation detection signal O.sub.D (also, in general, one bit) and counts it, supplying a detection scale increase request signal s.sub.UP_D, upon detection of a given number of saturation detection signals O.sub.D, for example two or three, but even just one.
(47) The OR gate 95 receives the detection scale increase request signal s.sub.UP_D and the prediction scale increase request signal s.sub.UP_P and generates a scale increase request for the logic stage 93 in presence of at least one of the above request signals s.sub.UP_D and s.sub.UP_P.
(48) The logic stage 93 also directly receives the detection scale increase request signal s.sub.UP_D.
(49) As shown in the flowchart of
(50) Then, as described in detail below, the replacement control signal s.sub.S supplied to the alignment block 63 is updated (step 204), the dithering conditions are possibly checked in the memory 99, in a per se known manner (step 206), and the dithering signals s.sub.D are possibly sent to the dithering blocks 57, 58 (step 208).
(51) Then, if the request for full scale increase is due to the detection of a saturation in progress (output Y from step 210), the sample replacement signal s.sub.S is supplied to the sample replacement block 61 and to the saturation detector/predictor block 60 (step 212).
(52) Instead, if a scale-decrease request s.sub.DW has been received (output Y from step 220), the logic stage 93 reduces the full scale (step 222), updating the current full scale signal s.sub.FS and the compensation enabling signal s.sub.SENS, and resetting all the counters 91, 92 and 96.
(53) In addition, the replacement control signal s.sub.S supplied to the alignment block 63 is updated (step 224), the dithering conditions are possibly checked in the memory 99 (step 226); and the dithering signals s.sub.D are possibly sent to the dithering blocks 57, 58 (step 228).
(54) According to a different embodiment (not shown), the increase counters 92, 94 may be omitted, and the logic stage 93 may modify the value of the current full scale signal s.sub.FS directly upon reception of one between the saturation detection signal O.sub.D and the saturation prediction signal O.sub.P.
(55) As may be noted, if, due to delays, the logic stage 93 receives both a scale increase request s.sub.UP and a scale-decrease request s.sub.SW, scale increase request is prioritized, since it is better to increase the full scale to no purpose (and in the worst case make an error equal to 1 LSB) rather than saturate and obtain a much larger error.
(56) As mentioned, when saturation is detected in step 212, the logic stage 93 issues a control for the alignment block 63 so that the latter selects the replacement sample S2 generated by the sample replacement block 61 and controls storing the replacement sample S2 instead of the normalized sample SN, through the replacement control signal s.sub.S. As mentioned, if the sensing system 50 includes the dithering blocks 57, 58, it may generate dithering signals s.sub.D in steps 208 and 228. In fact, as known, the above blocks insert a small error for reducing the quantization error and thus improving performance both of the ADC stage 53 and of the DSP stage 55 and may be enabled in the event of a high full scale. The dithering signals s.sub.D thus provide for dithering enabling/disabling, in addition to supplying the information of the current full scale.
(57) The alignment block 63 of
(58) The device described has the following advantages. It allows joining all the scales of the device in an automatic way for ensuring the improved dynamics for the signal, albeit maintaining the high sensitivity allowed by the dynamics. The joining is transparent to the stages downstream, which do not require modifications, apart from the capacity of working with a larger number of bits for the extended sample S3.
(59) The full scale adjustment stage 50 may be applied to MEMS micromachined sensors of different types, for example motion sensors, such as accelerometers, gyroscopes, magnetometers, etc.
(60) Finally, it is clear that modifications and variations may be made to the embodiments described and illustrated herein without thereby departing from the scope of the present disclosure.
(61) For example, when the sample replacement block 61 is implemented as sample interpolator 61B (
(62) Further, in the case of a multiaxial sensing system, it is possible to repeat some blocks of the diagram of
(63) In particular, in a multiaxial sensing system, it is possible to maintain a different full scale for each axis or have a single full scale for all the axes of the device. In the former case, since the axes are independent, the full scales are obtained independently of one another (unless some blocks are shared at different times). In the latter case (single full scale) it is sufficient to request change of the full scale of just one axis of the device to activate the procedure of assessment and possible change in the case of increase. Instead, the reduction of the full scale may be carried out only in presence of a request from all the axes. In this case, a decision block downstream of three decision blocks 62 in the three full scale change stages 54 manages change of the full scale, using a simple logic.
(64) The various embodiments described above can be combined to provide further embodiments. The embodiments may include structures that are directly coupled and structures that are indirectly coupled via electrical connections through other intervening structures not shown in the figures and not described for simplicity. Aspects of the embodiments can be modified, if necessary to employ concepts of the various patents, applications and publications to provide yet further embodiments. These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.