WO2022132212A1 - Procédés et systèmes permettant de déterminer une configuration d'acquisition robuste au bruit pour faire fonctionner un système de capteur - Google Patents

Procédés et systèmes permettant de déterminer une configuration d'acquisition robuste au bruit pour faire fonctionner un système de capteur Download PDF

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Publication number
WO2022132212A1
WO2022132212A1 PCT/US2021/022950 US2021022950W WO2022132212A1 WO 2022132212 A1 WO2022132212 A1 WO 2022132212A1 US 2021022950 W US2021022950 W US 2021022950W WO 2022132212 A1 WO2022132212 A1 WO 2022132212A1
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Prior art keywords
noise
scan
sensor
receive signal
signal
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PCT/US2021/022950
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English (en)
Inventor
Axel Heim
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Microchip Technology Incorporated
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Publication date
Priority claimed from US17/198,860 external-priority patent/US11916582B2/en
Application filed by Microchip Technology Incorporated filed Critical Microchip Technology Incorporated
Priority to JP2023511993A priority Critical patent/JP2023549624A/ja
Priority to CN202180059113.7A priority patent/CN116134407A/zh
Priority to DE112021006476.2T priority patent/DE112021006476T5/de
Priority to KR1020237003331A priority patent/KR20230117095A/ko
Publication of WO2022132212A1 publication Critical patent/WO2022132212A1/fr

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    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F3/00—Input arrangements for transferring data to be processed into a form capable of being handled by the computer; Output arrangements for transferring data from processing unit to output unit, e.g. interface arrangements
    • G06F3/01—Input arrangements or combined input and output arrangements for interaction between user and computer
    • G06F3/03—Arrangements for converting the position or the displacement of a member into a coded form
    • G06F3/041—Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means
    • G06F3/0416—Control or interface arrangements specially adapted for digitisers
    • G06F3/0418—Control or interface arrangements specially adapted for digitisers for error correction or compensation, e.g. based on parallax, calibration or alignment
    • G06F3/04182—Filtering of noise external to the device and not generated by digitiser components

Definitions

  • the present disclosure relates to methods and systems for determining a noise-robust acquisition configuration, in particular for a sensor system.
  • Sensor systems sometimes also referred as ‘sensing systems’ are known for various applications.
  • capacitive touch sensor systems are being used for user interfaces of electronic devices, such as computers, tablets, smart phones, and other electronic devices.
  • Capacitive touch sensor systems can be realized, for example, by generating an alternating electrical field and measuring the potential difference (i.e., the voltage) obtained in one cycle at a sensor electrode within this field.
  • a single electrode or a combination of a transmitting and one or more receiving electrodes may be used.
  • This voltage is a measure for the capacitance between the sensor electrode and its electrical environment, i.e., it is influenced by objects like a human finger or a hand.
  • an electric current flowing between an electrode and the sensor circuit i.e., motion of electrical charges
  • a problem with conventional systems operating according to the above-mentioned principle is that electrical noise sources, such as switched-mode power supplies, fluorescent lamps, or radio communication in the vicinity of the sensor can affect the electrical field. Thus, accurately and reliably estimating this voltage in a noisy environment is problematic.
  • a method of determining a noise-robust acquisition configuration for operation of a sensor system comprises the following steps in a noise scan: obtaining a sensor receive signal from the sensor system; determining a digital receive signal from the sensor receive signal by A/D conversion of the sensor receive signal at a predefined noise scan frequency; determining a plurality of decimated digital receive signals by integer decimation of the digital receive signal using two or more decimation rates that differ from each other, wherein each of the two or more decimation rates is associated with a respective candidate acquisition configuration; determining one or more noise measures for multiple of the candidate acquisition configurations using one or more of the plurality of decimated digital receive signals; and using the one or more noise measures, determining the acquisition configuration for operation of the sensor system from the candidate acquisition configurations.
  • a sensor circuit to determine an acquisition configuration for operation of a sensor system, comprising: a sensor interface for obtaining a sensor receive signal from the sensor system; an A/D converter to determine digital receive signal from the sensor receive signal by A/D conversion of the sensor receive signal at a predefined noise scan frequency; a decimation circuit, configured to determine a plurality of decimated digital receive signals by integer decimation of the digital receive signal using two or more decimation rates that differ from each other, wherein each of the two or more decimation rates is associated with a respective candidate acquisition configuration; a noise evaluation circuit, configured to determine one or more noise measures for multiple of the acquisition configurations using one or more of the plurality of decimated digital receive signals; and a configuration circuit, configured to determine the acquisition configuration for operation of the sensor system from the candidate acquisition configurations using the one or more noise measures.
  • a capacitive touch sensing system comprising: one or more electrodes, configured for capacitive sensing; and the sensor circuit of the preceding aspect, wherein the sensor circuit is connected to at least one of the one or more electrodes.
  • a method of determining a noise-robust acquisition configuration for operation of a communication system comprises the following steps in a noise scan: obtaining a receive signal from the communication system; determining a digital receive signal from the receive signal by A/D conversion of the receive signal at a predefined noise scan frequency; determining a plurality of decimated digital receive signals by integer decimation of the digital receive signal using two or more decimation rates that differ from each other, wherein each of the two or more decimation rates is associated with a respective candidate acquisition configuration; determining one or more noise measures for multiple of the acquisition configurations using one or more of the plurality of decimated digital receive signals; and using the one or more noise measures, determining the acquisition configuration for operation of the communication system from the candidate acquisition configurations.
  • a communication circuit to determine an acquisition configuration for operation of a communication system comprises: a communication system interface for obtaining a receive signal from the communication system; an A/D converter to determine digital receive signal from the receive signal by A/D conversion of the receive signal at a predefined noise scan frequency; a decimation circuit, configured to determine a plurality of decimated digital receive signals by integer decimation of the digital receive signal using two or more decimation rates that differ from each other, wherein each of the two or more decimation rates is associated with a respective acquisition configuration; a noise evaluation circuit, configured to determine one or more noise measures for multiple of the acquisition configurations using one or more of the plurality of decimated digital receive signals; and a configuration circuit, configured to determine the acquisition configuration for operation of the communication system from the candidate acquisition configurations using the one or more noise measures.
  • FIG. 1 shows a first exemplary embodiment of a sensor circuit in a schematic block diagram
  • FIG. 2 shows an exemplary embodiment of a capacitive touch sensing system in a schematic view
  • FIG. 3 illustrates the functionality of the sensor circuit of FIG. 1 in an exemplary flow diagram according to a first embodiment
  • FIG. 4 schematically illustrates the functionality of a decimation circuit of the sensor circuit of FIG 1;
  • FIG. 5 schematically illustrates two signal processing chains for a noise scan and an SN-scan
  • FIG. 6 illustrates the functionality of the sensor circuit of FIG. 1 in an exemplary flow diagram according to a second embodiment
  • FIG. 7 shows exemplary magnitudes of an ideal ADC’s transfer function in a schematic diagram
  • FIGS. 8 A and 8B illustrates the functionality of the sensor circuit of FIG. 1 in an exemplary flow diagram according to a further embodiment
  • FIG. 9 illustrates spectral noise suppression by digital LPF
  • FIG. 10 illustrates the functionality of the sensor circuit of FIG. 1 in an exemplary flow diagram according to another embodiment
  • FIG. 11 shows a basic exemplary diagram for charge measurement using current integration and a corresponding timing diagram
  • FIG. 12 shows another exemplary diagram for charge measurement using two current integrators together with a corresponding timing diagram
  • FIG. 13 schematically shows two slices of an exemplary analog front-end (AFE) of a touchscreen controller
  • FIG. 14 shows an exemplary timing diagram for current integration and integrator resetting with slice-independent control of aperture and reset switches
  • FIG. 15 shows an exemplary timing diagram for current integration and integrator resetting without slice-independent control of aperture and reset switches
  • FIG. 16 shows data obtained using the timing configuration of FIG. 15.
  • FIG. 17 illustrates spectral noise suppression by digital LPF for two packet lengths.
  • connection is used to indicate a data or signal connection between at least two components, devices, units, processors, circuits, or modules.
  • a connection may be direct between the respective components, devices, units, processors, circuits, or modules; or indirect, i.e., over intermediate components, devices, units, processors, circuits, or modules.
  • the connection may be permanent or temporary; wireless or conductor based; digital or analog.
  • ordinal numbers e.g., first, second, third, etc.
  • an element i.e., any noun in the application.
  • the use of ordinal numbers is not to imply or create any particular ordering of the elements nor to limit any element to being only a single element unless expressly disclosed, such as by the use of the terms "before”, “after”, “single”, and other such terminology. Rather, the use of ordinal numbers is to distinguish between like-named elements. For example, a first element is distinct from a second element, and the first element may encompass more than one element and succeed (or precede) the second element in an ordering of elements.
  • sensor systems are used.
  • electronic devices such as smart phones, laptops, tablets, wearables
  • touchscreens which generally use capacitive or resistive touch sensor systems.
  • Current developments increase the use of touchscreens in more complex systems, such as cars, airplanes, or industrial equipment.
  • Touch report rate hereby refers to the rate at which a touch controller forwards, for example, (x,y) position estimates to a host controller.
  • the operating frequency in case of a capacitive sensor system the operating frequency of a so-called ‘stimulus signal’
  • the set of configurable parameters of the sensor system that influence these impact factors is understood as the ‘acquisition configuration’ or ‘data acquisition configuration’ of the sensor system (in the following also referred to as ‘AC’ for simplicity).
  • the acquisition configuration comprises at least one or more of the following parameters: a sampling frequency for A/D conversion, an operating frequency (carrier frequency) of a stimulus signal for (acquisition) operation of the sensor system, scan duration, a number of samples to be acquired, ‘packet length’, and low-pass filter coefficients. Different ACs differ in one or more of these parameters.
  • the parameters may be used to configure the ‘analog front-end’ as well as the digital processing of the sensor control circuit.
  • the receive signal of a communication or sensing system typically is a mixture of the actual information that needs to be received and evaluated, as well as noise.
  • This information can, for example, be a measure for the capacitance or distance between a sensor electrode and a user’s finger.
  • the receive signal simply is the sum of information and noise. Because typically both the information part and the noise part are unknown, the information part cannot be easily extracted from the receive signal - comparable to one equation with two unknowns which cannot be solved uniquely. What is possible however is estimating the information part given the noisy receive signal while making assumptions about properties of information, noise or both, e.g., ‘the information is varying slowly over time’.
  • noise scans It is possible to conduct a test measurement with the sensor system and to compute a noise measure from this measurement data, which is representative for the amount of noise. Such test measurements are in the present context referred to as ‘noise scans’.
  • Noise scans may be conducted for different candidate ACs, and given the respective noise determined, the AC for which the lowest amount of noise was yielded can be selected. Measurements where the receive signal contains both the desired information and noise will be referred to as signal-and-noise scan, or ‘SN-scan’.
  • the sensor or communication system may need to create and emit a stimulus signal to excite an alternating electric field and to yield the information part at the receive side.
  • estimates of the amount of noise to be expected during an SN-scan for pre-defined candidate ACs can be computed.
  • noise estimate is referred to as ‘noise estimate’.
  • the ACs for which noise estimates are computed from noise scan data acquired during a single noise scan may differ at least in their operating frequency and sampling frequency, which are considered parameters of the analog front-end of the sensor system.
  • a ‘stimulus signal’ is understood as an actively controlled movement of electrical charges between a sensor circuit, e.g., a chip, and an electrode, for example to drive the electrode’s electrical potential to a given target value or target signal.
  • this target value or target signal is specified before the stimulus is initiated; for example, when the target signal is a rectangular pulse train with a given pulse frequency, this pulse frequency is selected before driving the electrode’s electrical potential to this target signal.
  • the stimulus may be a periodic signal, e.g., a rectangular pulse train.
  • the frequency of this periodic signal e.g. the pulse frequency, is the operating frequency discussed in the preceding, also referred to as ’carrier frequency’.
  • the stimulus signal settles alternately to a higher signal level and a lower signal level each once during a carrier signal period.
  • the receive(d) signal may be demodulated and low-pass filtered - both of which may be performed in the digital domain after analog-to- digital (A/D) conversion.
  • sampling may be conducted at twice the carrier frequency in some embodiments.
  • Demodulation may be conducted by alternatingly multiplying the A/D converted samples with plus one and minus one in some embodiments.
  • a need addressed by embodiments of the invention is to select a suitable AC from a set of candidate ACs in order to achieve, e.g., a high touch report rate with reliable and accurate output estimates.
  • Basic exemplary ideas of the invention comprise a) the idea of base- and sub- frequencies, allowing to process the same sequence of noise scan measurement data in different ways, more precisely with different parameters, in order to yield reliable noise (power) estimates for multiple ACs (for example with respect to carrier frequencies and scan times), and b) a robust noise measure providing an accurate estimate for the true noise power of SN- scan measurement data after demodulation and low-pass filtering.
  • a method of determining a noise-robust acquisition configuration for operation of a sensor system comprises the following steps in a noise scan: obtaining a sensor receive signal from the sensor system; determining a digital receive signal from the sensor receive signal by A/D conversion of the sensor receive signal at a predefined noise scan frequency; determining a plurality of decimated digital receive signals by integer decimation of the digital receive signal using two or more decimation rates that differ from each other, wherein the two or more decimation rates are associated with a respective candidate acquisition configuration; determining one or more noise measures for multiple of the candidate acquisition configurations using one or more of the plurality of decimated digital receive signals; and using the one or more noise measures, determining the acquisition configuration for operation of the sensor system from the candidate acquisition configurations.
  • the sensor system of the present aspect may be of any suitable type, including, without limitation, sensor systems to detect and measure proximity, pressure, position, displacement, force, humidity, fluid level, and acceleration.
  • the sensor system may be an infrared sensor system or an ultrasound sensor system.
  • the sensor system may be a capacitive or resistive touch sensor system, such as for a touchscreen display.
  • the sensor system may be a touch-less sensor system.
  • the method of the present aspect is conducted using a sensor circuit, for example a sensor circuit comprising a control unit, such as a microcontroller and/or microprocessor with suitable programming.
  • the sensor circuit may comprise dedicated circuitry that provides at least a part of the functionality of the method of this exemplary aspect.
  • the (sensor) receive signal (i.e., a received, measured or acquired signal during a noise scan or SN-scan) may be, for example, an electric current flowing between an electrode and the sensor circuit, i.e., motion of electrical charges, an electric current integrated over a certain time interval, or an electric potential or voltage of the electrode relative to a reference potential.
  • the sensor receive signal may be obtained from the sensor system by any suitable means, for example a corresponding conductive connection.
  • This receive signal may be affected by the stimulus when used, possibly modified by environmental factors like a human finger, and is in most circumstances affected by environmental noise sources.
  • environmental noise sources In addition to these environmental, or external, impact factors, there can be analog pre-processing within the sensor circuitry which can add further internal noise to the receive signal, for example 1/f noise or quantization noise of an A/D converter. While robustness to noise from internal sources typically can be addressed during system design, environmental noise sources are at least to some extent unknown at design time. The methods and systems discussed herein address robustness to external noise. Disregarding internal noise, any change in the receive signal, i.e., any electric current or change in above electric potential, is caused by this external noise of interest.
  • the method comprises determining a digital receive signal from the sensor receive signal by A/D conversion of the sensor receive signal at a predefined noise scan frequency.
  • A/D conversion may be conducted using any suitable method, for example using a flash A/D converter, an integrating A/D converter, a successive approximation A/D converter, a sigma-delta A/D converter, a direct-conversion A/D converter, a ramp-compare A/D converter, a Wilkinson A/D converter, a charge balancing A/D converter, a dual-slope A/D converter, a delta-encoded A/D converter, a pipelined A/D converter, a time- interleaved A/D converter, an intermediate FM stage A/D converter, a TS-ADC, or any equivalent, without limitation.
  • A/D converter herein includes setups of an analog front-end with a suitable A/D converter.
  • A/D conversion is conducted at the predefined noise scan frequency that may be set depending on the application.
  • the noise scan frequency is significantly higher than an operating frequency of a stimulus signal during operation of the sensor system.
  • the noise scan frequency may be set to at least three times the operating frequency, such as between 3x - 40x of the operating frequency.
  • the noise scan frequency is set between 3x - 4x of the operating frequency.
  • the noise scan frequency i.e., the sampling rate of the A/D converter during a noise scan
  • the sampling interval of the A/D converter may be significantly shorter for a noise scan as compared with an SN-scan, and so is the time available for the analog processing of the received input signal for an analog-to-digital (A/D) converted sample. Consequently, the timing for analog processing desired for an SN-scan may not be applicable to a noise scan because there is less time between A/D conversions.
  • Embodiments are discussed in the following using a specific ratio of an aperture time for a noise scan to an aperture time for an SN-scan.
  • the method comprises determining a plurality of decimated digital receive signals by integer decimation of the digital receive signal using two or more decimation rates that differ from each other.
  • the two or more decimation rates are associated with respective candidate acquisition configurations, e.g., in light of the resulting differing sampling rates when applying the different decimation rates.
  • one or more noise measures for multiple of the candidate acquisition configurations are determined using one or more of the plurality of decimated digital receive signals.
  • the acquisition configuration for operation of the sensor system is determined from the candidate acquisition configurations.
  • oversampling is conducted during a noise scan. Then, to yield the same aliasing (of noise) as for an SN-scan, the decimation rate for decimating the noise scan signal may for example be chosen such that the decimated sampling rate equals the SN- scan sampling rate.
  • the teachings herein at least in some embodiments, not only provide a solution for identifying a relatively best carrier frequency, but a complete solution for noise robustness. Robustness to, e.g., AM noise and square noise is provided due to the determination of the one or more noise measures from the same measurement data but for different ACs. This method also is inherently quick and saves measurement time. In some embodiments, the method further allows finding a trade-off between touch report rate and output SNR.
  • the method of the first exemplary aspect comprises determining one or more noise measures for multiple of the (two or more) candidate acquisition configurations from one or more of the plurality of the decimated digital receive signals.
  • the determination of the noise measures may, for example, be conducted in the digital domain.
  • one or more noise measures are determined for each of candidate acquisition configurations, which allows for comparison of different candidate ACs.
  • a noise measure is calculated for each decimation rate from at least one decimated digital receive signal that is associated with the respective decimation rate.
  • a noise measure is calculated for each decimation rate from multiple decimated digital receive signals. This method will be discussed in more detail in the following.
  • the noise measure in some embodiments may be a power measure as, for example, obtained by effective noise power estimation (ENPE), but it may also be, for example, a square root of a power measure or another linear measure, i.e., a quantity computed from input data using linear functions only, without limitation.
  • the noise measure is a phase-instantaneous noise measure.
  • the noise measure is a scoring value where a higher score indicates a lower noise level for an SN-scan, as for example discussed in US 10151608 B2, incorporated herein for all purposes.
  • the acquisition configuration for operation of the sensor system is determined from the given candidate acquisition configurations.
  • the present determination is based on the one or more noise measures.
  • the determination may be influenced by further considerations, such as for example a shortest scan time (also referred to as ‘scan duration’).
  • the preferred noise measure is selected based on a predefined criterium, such as for example based on a predefined threshold of maximum noise.
  • corresponding groups of decimated digital receive signals are determined as a part of the determination of the plurality of decimated digital receive signals. Accordingly, and in view of the two or more decimation rates, at least two groups of decimated digital receive signals are provided according to the present embodiments, wherein the group ‘members’ of one group share the same decimation rate.
  • the decimated digital receive signals may differ from each other at least, but without limitation, by having a different starting phase.
  • starting phase with respect to digital signals is understood as the delay of a decimated signal’s first sample relative to the digital receive signal’s first sample, typically in the unit of samples at the receive signal’s sampling rate. Accordingly, a different starting phase with respect to two signals refers to that the two signals have differing starting samples.
  • a group of decimated digital receive signals represent all possible starting phases.
  • the group would comprise four corresponding decimated digital receive signals with six samples each, and each signal starting at a different starting phase of the total of four possible starting phases. While each of the decimated digital receive signals of the group only comprises every fourth sample, due to the phase shift of one sample, every sample is still represented in the group resulting in an improved noise measure.
  • the one or more noise measures are determined by an effective noise power estimation (ENPE), which comprises a determination of a (e.g., normalized) sum of phase-instantaneous noise measures over each of the decimated digital receive signals of one of the groups of decimated digital receive signals.
  • ENPE effective noise power estimation
  • the effective noise power estimation is conducted for all groups, i.e., for all decimation rates.
  • the determination of the sum of phase-instantaneous noise measures can be conducted by any suitable method.
  • the phase-instantaneous noise measure is a sum of (all) samples of a decimated digital receive signal weighted with coefficients from a coefficient vector.
  • the coefficient vector may be a vector containing the coefficients of a low-pass filter.
  • the coefficients of a boxcar window can, for example, be done by dividing this sum term by the sum of all coefficients in the coefficient vector. This normalization does not need to be done directly on the weighted sum term, but can also be done at later processing stage, e.g. after summing of phase-instantaneous noise measures, which can reduce computational complexity.
  • the dot product with the assigned coefficient vector is computed.
  • these dot products are normalized by dividing by the sum of all coefficients. Then the average of the squared normalized dot products may be computed to yield the ENPE.
  • the step of determining the acquisition configuration from the set of candidate acquisition configurations comprises selecting the candidate acquisition configuration that has the shortest scan time while the noise measure meets a (predefined) noise threshold.
  • the present embodiments provide a particularly high touch report rate as the shortest possible scan time is employed.
  • SNR expected output signal-to- noise ratio
  • the step of determining the acquisition configuration from the set of candidate acquisition configurations further comprises comparing the one or more noise measures with a noise threshold and in case the noise threshold is not met by any of the one or more noise measures, increasing the scan time of at least one of the candidate acquisition configurations to obtain at least one updated candidate acquisition configuration, determining one or more updated noise measures for the at least one updated candidate acquisition configuration, and comparing the one or more updated noise measures with the noise threshold.
  • the present embodiments allow to gradually evaluate candidate acquisition configurations with increased scan time in case none of the original candidate acquisition configurations meets the desired noise threshold, which may, e.g., be set in accordance with the respective application.
  • the discussed steps may be repeated until an acquisition configuration is found that meets the noise threshold.
  • the candidate acquisition configuration is selected as acquisition configuration for system operation that has the lowest noise level for the scan time of the given iteration.
  • the scan time of multiple or all candidate acquisition configurations is increased in a given iteration of the preceding steps. This provides multiple updated candidate acquisition configurations that may have the same operating and sampling frequency, but different coefficient vectors.
  • the scan time is increased by a substantially integer multiple of a scan time of the original/preceding candidate acquisition configuration. These embodiments are particularly beneficial for reducing noise.
  • a ‘substantially integer multiple’ comprises percentage deviations from the integer multiple of approx. , where T is the original scan time.
  • a new noise scan may be conducted with a correspondingly increased scan time to obtain the at least one updated candidate acquisition configuration.
  • the step of obtaining the sensor receive signal from the sensor system it is possible during the step of obtaining the sensor receive signal from the sensor system to obtain a sensor receive signal with a maximum scan time and consider only a portion of it initially. For example and in some embodiments, after the A/D conversion is conducted, only a portion of the sensor receive signal is processed further and forms the basis for the discussed decimation, namely with a minimum scan time, while the original sensor receive signal is stored. In these embodiments, it is possible to ‘increase’ the scan time by subsequently using a longer portion of the stored copy of the original sensor receive signal, i.e., with increased scan time. In some embodiments, the maximum scan time may be four times the minimum scan time.
  • a predefined minimum output report rate for the sensor system may be given, or, inversely, a maximum duration for a scan cycle (i.e., the successive operation of one or more noise scans and an SN-scan) during which respective measurement data is acquired.
  • This time available for a scan cycle is distributed over all individual measurements to be done during the scan cycle, including auxiliary measurements like a noise scan and at least one SN-scan.
  • auxiliary measurements like a noise scan and at least one SN-scan.
  • T For example, for one individual measurement of an SN-scan we may thus yield a maximum scan time T.
  • Given an AC with sampling frequency being twice the operating frequency or carrier frequency f c it is possible to fit up to ADC samples into time T.
  • the 'packet length’ L for the given AC to .
  • the filter length may also be set to L in order to make use of all of the acquired data, and because a single output value for the data acquired during scan time T may be desired, while requiring the low-pass filter output to have settled.
  • the vector of low-pass filter coefficients may be chosen, for example, to control the filter’s spectral suppression in some embodiments.
  • the vector’s first elements can be positive values smaller than the middle elements of the vector.
  • such a vector can be [0.05, 0.1, 0.2, 0.3, 0.2, 0.1, 0.05],
  • the vector symmetric.
  • the n-th element of the Hanning window is
  • the method comprises operating the sensor system during an SN-scan using the acquisition configuration determined during the noise scan.
  • the sensor system may be operated to emit a stimulus signal to excite an alternating electric field, which then can be evaluated for the respective sensing application, such as a touch detection.
  • the sensor system is operated during the SN-scan using the acquisition configuration of the latest noise scan in view that the acquisition configuration of the latest scan represents the most up-to-date configuration for a current noise scenario.
  • a further noise scan is conducted following the SN-scan. The resulting cycled operation may be repeated until the sensing operation of the sensor system stops in some embodiments, such as when the sensor system is powered down.
  • an overall acquisition configuration for operation of the sensor system from acquisition configurations obtained during the subsequently conducted multiple noise scans.
  • a ‘preferred’ or ‘best’ overall acquisition configuration may be determined from the multiple acquisition configurations obtained in each run of a noise scan.
  • the overall acquisition configuration may be determined from the group of acquisition configurations, determined during the multiple noise scans, by comparing the associated noise measures and/or respective scan times.
  • noise scans for, e.g., only two (or a different number of) predefined noise scan frequencies successively during a scan cycle, while keeping the one yielding the best AC, and cyclically looping over the remaining candidate noise scan frequencies to select the second one.
  • the aperture time of the A/D conversion for determining the acquisition configuration is set to be substantially identical to, or an integer fraction of the aperture time of an SN-scan.
  • an aperture time is predefined, or selected as desired, for the SN-scan according to the respective application (e.g., in terms of touch report rate) and the aperture time for the A/D conversion during the noise scan is set accordingly, i.e., identical or an integer fraction of the predefined aperture time.
  • the term “aperture time” generally is understood as the time duration for which an analog signal is input to a measurement system, i.e., the time during which the measurement system is exposed to the outside world and thus its internal analog state is changed by the analog input signal.
  • the aperture time relates to the time the sensor receive signal is input to the sensor interface of the sensor circuit, discussed in the following.
  • the aperture time relates to the time the sensor receive signal is input to the A/D converter of the sensor circuit, discussed in the following.
  • the noise scan aperture time is identical to the SN-scan aperture time, it is possible to ensure to yield a relatively best carrier frequency decision.
  • the noise scan aperture time is an integer fraction of the SN-scan aperture time, and the noise is narrow-band, it is still possible to yield a best carrier frequency, though an absolute effective noise power estimate cannot be provided.
  • the noise scan aperture time is either a) identical to the SN-scan aperture time, or b) when the noise scan aperture time is an integer fraction of the SN-scan aperture time or correspondingly, when the SN-scan aperture time is an integer multiple of the noise scan aperture time.
  • the duration is approximately the same for all index pairs (i,j).
  • the method steps are conducted at least in part by a sensor circuit for a sensor system.
  • a (e.g., non-transitory) computer-readable medium is provided with contents that are configured to cause the sensor circuit to conduct the method steps as described herein.
  • a sensor circuit to determine an acquisition configuration for operation of a sensor system comprises, but is not limited to: a sensor interface or input for obtaining a sensor receive signal from the sensor system; an A/D converter to determine a digital receive signal from the sensor receive signal by A/D conversion of the sensor receive signal at a predefined noise scan frequency; a decimation circuit, configured to determine a plurality of decimated digital receive signals by integer decimation of the digital receive signal using two or more decimation rates that differ from each other, wherein each of the two or more decimation rates is associated with a respective candidate acquisition configuration; a noise evaluation circuit, configured to determine one or more noise measures for multiple of the candidate acquisition configurations using one or more of the plurality of decimated digital receive signals; and a configuration circuit, configured to determine the acquisition configuration for operation of the sensor system from the candidate acquisition configurations using the one or more noise measures.
  • the sensor circuit according to the present aspect is configured according to one or more of the embodiments, discussed in the preceding with respect to the preceding aspect(s). With respect to the terms used and their definitions, reference is made to the preceding aspect(s).
  • a sensor circuit according to the present aspect is configured according to one or more of the embodiments, discussed in the preceding with respect to the preceding aspect(s). With respect to the terms used and their definitions, reference is made to the preceding aspect(s).
  • the term “capacitive touch sensing system” used herein is understood to comprise touch-less sensor systems, e.g., based on a detection of proximity.
  • the described components of the embodiments each represent individual features that are to be considered independent of one another, in the combination as shown or described, and in combinations other than shown or described.
  • the described embodiments can also be supplemented by features of the invention other than those described.
  • FIG. 1 shows a first exemplary embodiment of a sensor circuit 1 in a schematic block diagram.
  • the sensor circuit 1 is adapted to operate a sensor system or a communication system (both not shown in FIG. 1).
  • a sensor 20 of a capacitive touch sensing system 21, shown schematically in FIG. 2 may be connected to sensor circuit 1.
  • capacitive touch sensing system 21 even though it is emphasized that the invention is not limited to capacitive touch sensing systems.
  • the exemplary sensor circuit 1 of the embodiment of FIG. 1 may be embodied by a microcontroller, with hardware/software that provides the following operation and components. For improved clarity, the microcontroller itself is not shown in the schematic block diagram of FIG. 1.
  • the sensor circuit 1 comprises a sensor interface 2, which is connectable to the sensor 20 of capacitive touch sensing system 21, using sensor connections 3.
  • Capacitive touch sensing is known, for example, for use in capacitive touch screen panels of electronic devices, such as computers, tablets, smart phones, wearables, and smart home equipment, and electronic components for vehicles, trains, ships, air-/spacecraft, and industrial or scientific equipment, without limitation.
  • the capacitive touch sensing system 21 is a ‘touch-less’ sensor system.
  • the sensor interface 2 and sensor connections 3 allow the sensor circuit 1 to operate/drive the sensor 20 of capacitive touch sensing system 21 during acquisition operation, which is referred to herein as ‘signal-and-noise scan’, or SN-scan.
  • the sensor circuit 1 or more precisely a drive circuit 4 of sensor circuit 1 creates and transmits a stimulus signal to excite an alternating electric field near the sensor 20 of capacitive touch sensing system 21, which then yields the information part at the receive side, namely with respect to the capacitive touch sensing, whether one or more fingers of a user or a different object are detected close to the surface of sensor 20. Both, the transmission of the stimulus signal and the reception of a returning sensor receive signal is handled by sensor interface 2.
  • the stimulus signal is a periodic signal, namely a rectangular pulse train.
  • the frequency of this periodic signal i.e., the pulse frequency, is referred to as the operating frequency or carrier frequency of the SN-scan.
  • sensor circuit 1 conducts noise scans in a corresponding noise scan mode. During a noise scan, preferably no stimulus signal is applied to the sensor by the sensor circuit 1.
  • the noise scans serve as test measurements and allow computation of noise measures from measurement data obtained during the noise scans, which are representative of the amount of noise to be expected during an SN-scan.
  • Robustness to noise is a key challenge for any communication system or sensor system, including capacitive touch sensing system 21.
  • capacitive touch sensing system 21 Particularly, the passing of standard IEC conducted noise tests, e.g., with amplitude modulated noise as in IEC 61000-4-6, bulk current injection (BCI) tests, e.g. according to the ISO 11452-4 automotive standard, or robustness to square noise is addressed.
  • BCI bulk current injection
  • a goal of conducting the noise scans is to determine an acquisition configuration for operation of the capacitive touch sensing system 21 during an SN-scan.
  • the acquisition configuration comprises one or more parameters for the operation of the capacitive touch sensing system 21 during an SN-scan and may comprise one or more of a sampling frequency for A/D conversion, an operating frequency (carrier frequency) of the stimulus signal for (acquisition) operation of the sensor system, scan duration, a number of samples to be acquired, and low-pass filter coefficients.
  • the sampling frequency for A/D conversion during an SN-scan is considered to be related to the operating frequency / carrier frequency of the stimulus signal.
  • the sensor receive signal in the present embodiment is a quasi-static signal, i.e., a signal which does not, or only hardly, changes over time during given time intervals, in view of the stimulus signal in the shape of a rectangular pulse train.
  • the signal has experienced low-pass filtering, its edges are rounded and after each edge it shows a transition duration until it settles to a constant level.
  • the received signal is sampled once after each edge when the signal has settled to a sufficient extent, i.e., there are two samples per period of the rectangular pulse train during the SN-scan, thus corresponding to the sampling frequency being twice the carrier frequency.
  • Sensor circuit 1 further comprises A/D converter 5, digital signal processing circuit 15, noise evaluation circuit 8, configuration circuit 9, memory 10, touch detector 11, and output 12.
  • the digital signal processing circuit 15 comprises in particular a decimation circuit (not shown in FIG. 1) that is configured to determine a plurality of decimated digital receive signals, as discussed in more detail in the following. It is noted that FIG. 1 does not show all control connections between the aforementioned components, e.g., for controlling the sampling rate of A/D converter 5 or access of memory 10 by signal processing circuit 15.
  • the signal processing chain of A/D converter 5, digital signal processing circuit 15, noise evaluation circuit 8, and configuration circuit 9 is active.
  • the noise evaluation circuit 8, and the configuration circuit 9 are disabled, or inactive.
  • the sensor receive signal, after A/D conversion and signal processing is provided to touch detector 11 for determination of a user touch on the sensor 20. The result is provided to a connected external component via output 12.
  • sensor circuit 1 The functionality of sensor circuit 1 and its components will in the following be explained referring to FIG. 1 and the flow diagram FIG. 3.
  • exemplary capacitive touch or touch- less sensing system 21 has a multitude of acquisition configurations, whose analog front-end parameters are equal but for the operating frequencies and the respective sampling frequencies, the latter of which, as discussed in the preceding, are twice the carrier frequencies in this exemplary embodiment.
  • the different sampling frequencies have a common multiple, which is the predefined noise scan frequency.
  • Other, digital signal processing parameters like the number of samples to be filtered and the choice of low-pass filter coefficients, may or may not differ between these ACs.
  • a noise scan begins in step 30 with the initialization / power-up of sensor circuit 1.
  • the sensor receive signal is obtained from the sensor 20 using the sensor interface 2, as discussed in the preceding, without a stimulus signal being applied. The signal thus only comprises noise.
  • the sensor receive signal subsequently in step 32 is A/D converted using the A/D converter 5 to obtain a digital sensor receive signal.
  • data is acquired at a frequency f b which we denote as the base frequency or predefined noise scan frequency.
  • decimated digital receive signals are generated by the decimation circuit of digital signal processing circuit 15 from the digital sensor receive signal. Decimation of the digital sensor receive signal reduces the number of samples in the respective decimated digital receive signal.
  • decimation with multiple decimation rates allows that multiple possible ‘candidate’ acquisition configurations can be evaluated from the same measurement data, i.e., the digital sensor receive signal.
  • the (candidate) acquisition configurations in this embodiment have sampling frequencies of which the noise scan sampling frequency is a common multiple. Low-pass filter lengths and coefficient values may differ as well in some examples.
  • Decimation of the noise scan digital sensor receive signal with multiple decimation rates provides decimated digital receive signals with these different sampling frequencies and thus makes it possible to evaluate the different candidate acquisition configurations using the same sensor receive signal. As will be apparent from the example in FIG.
  • the digital signal processing circuit 15 demodulates the decimated digital receive signals. This is conducted herein, without limitation, by multiplication of the samples altematingly with plus one and minus one as it would also be done during an SN-scan.
  • digital low-pass filtering e.g., using one or more finite impulse response (FIR) filters
  • FIR finite impulse response
  • different decimation rates R may require differences in the further processing, in particular, the number of filter coefficients of the FIR filters may be equal to the number of samples after decimation, i.e. equal to the packet length L of the respective candidate AC, and the values of the filter coefficients may differ for different decimation rates R accordingly.
  • filtering is applied using a Hanning window of length L as the vector of low-pass filter coefficients.
  • the n-th element of the Hanning window is
  • Evaluation is done in step 35 by the noise evaluation circuit 8 that determines noise measures for the candidate acquisition configurations from the decimated digital receive signals.
  • a group of decimated digital receive signals is determined.
  • an ‘effective noise power estimate’ also referred to as ‘ENPE’.
  • the set of employed signal phases can also be a subset of the full set of phases ⁇ 0,1, ..., R — 1 ⁇ , for example ⁇ 0,2,4, ... , R — 1 ⁇ .
  • each group of decimated digital receive signals does not necessarily comprise all possible signal phases.
  • each decimation rate R is assigned a coefficient vector with the same length as the decimated signals, for example containing the coefficients of an FIR low-pass filter (LPF).
  • LPF FIR low-pass filter
  • the dot product with the assigned coefficient vector is computed in step 35 by noise evaluation circuit 8.
  • these dot products may be normalized by dividing by the sum of all coefficients. Then the average of the squared normalized dot products is computed to yield the ENPE.
  • FIG. 4 shows how for each R G ⁇ 2, 3, 4, 6 ⁇ the original signal vector is split into up to R signal vectors where we denote , and v ⁇ ⁇ 0,1, ... , R — 1 ⁇ .
  • phase-instantaneous noise measure ensures a filter DC gain of 1 and can be moved out of the sum over the phases v - then being squared - or can be considered in a later processing step, leaving .
  • the ENPEs are passed to configuration circuit 9, which selects the acquisition configuration for operation of the sensor system from the candidate acquisition configurations using the determined ENPEs in step 36.
  • the configuration circuit 9 determines in step 36, which of the candidate acquisition configurations yields the lowest noise by evaluating the associated ENPEs.
  • the noise scan is complete.
  • the acquisition configuration is provided to drive circuit 4 by the configuration circuit 9.
  • the selected acquisition configuration is stored in memory 10 for future reference.
  • the capacitive touch sensing system 21 is then operated in at least one SN-scan (step 37) according to the results of the noise scan. It is noted that an SN-scan may be conducted for multiple sensor (transmit) lines 3, particularly in case of mutual-capacitance sensors. After the SN-scan(s), a new noise scan is conducted, beginning with step 30.
  • the two resulting signal processing chains for the noise scan and the SN-scan are shown in FIG. 5 in a simplified and schematic diagram.
  • FIG. 5 shows the digital processing for data acquired during an SN-scan.
  • the digital ADC output signal i.e. the digital sensor receive signal, is then provided to the digital signal processing circuit 15, which comprises a demodulator 13, an FIR low pass filter 6, and a decimation circuit 7.
  • the digital ADC output signal i.e.
  • the digital sensor receive signal is demodulated by the demodulator 13 by multiplying its samples altematingly with plus and minus one, and the demodulated signal is input into the digital low-pass LPF filter 6 with L filter coefficients and finally decimated with factor L, i.e., only one sample is output of the decimator 7 after inputting L samples.
  • FIG. 5 the processing of the digital processing circuit 15 and the noise evaluation circuit 8 during the noise scan is shown in more detail.
  • the ADC 5 is sampling the analog sensor receive signal at the predefined noise scan frequency.
  • FIG. 5 the processing of one exemplary AC is shown. The operation would be conducted for each AC to be considered.
  • each of the demultiplexed signals is demodulated by a respective demodulator 13 by multiplying its samples altematingly with plus and minus one, and each demodulated signal is being filtered in an FIR low-pass filter LPF 6 and decimated by decimation circuit 7.
  • each ADC sample x k may be discarded as soon as it has been multiplied with ( ⁇ 1) yielding the demodulated value as an intermediate product
  • the samples x k may be stored in memory 10 for offline processing.
  • the processing, discussed with reference to FIGS. 3 and 5, is initiated after A/D conversion.
  • FIG. 6 shows an exemplary flow diagram of the operation of sensor circuit 1 in another embodiment.
  • the operation corresponds to the preceding discussion, in particular referring to FIG. 3.
  • configuration circuit 9 is connected to A/D converter 5 (not shown in FIG. 1).
  • the aperture time is set back to the original aperture time in step 60 upon the next noise scan cycle.
  • the present embodiment is based on the inventor’s recognition that, when capturing analog data to create a time-discrete sample, the time duration for which the analog signal is input to the measurement system, i.e., the time during which the measurement system is exposed to the outside world and thus its internal analog state is changed by the analog input signal, can affect the output sample’s value.
  • this time duration is the so-called ‘aperture time’.
  • an electrical current flowing to or from a sensor electrode is being integrated for a deterministic amount of time.
  • This integration time also is considered to be an aperture time.
  • the aperture time cannot be longer than the time between two successive samples, the sample interval, because the aperture time windows of two successive samples cannot overlap.
  • the higher the sampling frequency the shorter the sample interval and thus the shorter the maximum aperture time.
  • the maximum aperture time 1/(2 • R • f c ) is shorter than during an SN-scan where the sampling frequency is 1/(2 • f c ).
  • a desired aperture time may also depend on the sensor type at hand. For example, signal settling times are typically higher for ITO sensors than for PCB sensors due to the lower conductivity of ITO compared to copper. Therefore, a longer aperture time may be desired for an ITO sensor compared to a similarly shaped PCB sensor. It is noted that there are also cases where the aperture time has a practically negligible effect onto the measurement values. These may include, for example, voltage measurements done on the output of a voltage follower circuit ('buffer amplifier’). It is however possible in certain scenarios that a desired aperture time is shorter than the SN-scan sample interval but exceeds the noise scan sample interval. Then, obviously, the desired aperture time is not applicable to the noise scan. A different, shorter aperture time may be chosen for the noise scan.
  • the noise scan aperture time is an integer fraction of the SN-scan aperture time or correspondingly, when the SN-scan aperture time is an integer multiple of the noise scan aperture time. This is shown by way of example in FIG. 7 for the fraction 1/3 when all ‘noise-scan zeros’ (integration time 0.833us) fall onto ‘SN-scan zeros’ (integration time 2.5us).
  • the ENPE provides an absolute estimate for the noise power of a received signal after demodulation and low-pass filtering. For some sensor systems or applications there may be an upper threshold for this noise power above which operation is not desirable.
  • One exemplary approach to yield a lower noise power is to increase the number L of acquired and processed samples, denoted herein the ‘packet length’, and thus the filter length equal to L.
  • increasing the packet length alone and by itself does not generally improve noise suppression.
  • Noise suppression is dependent primarily on the chosen low-pass filtering of which the packet and filter length is only one aspect.
  • FIG. 17 shows an example of the spectral noise suppression in case the packet size is increased from 5 to 7 samples for boxcar window and Hanning window. For example, in the top plot with boxcar window, the noise susceptibility is increased for the normalized frequency radians/sample, not decreased.
  • Hanning window For boxcar, Hann window, and Matlab’s Hanning window (a Hanning window herein corresponds to a Hann window with the first and last sample removed) low-pass filters the rule how to increase a packet length L to L’ in order to guarantee improved noise suppression for all noise frequencies is
  • a minimum report rate i.e., capacitive touch or touch-less sensing system 21 may be required to output estimated data at a report rate equal to, or higher than, a minimum report rate.
  • This estimated data can, for example, be low- pass filtered and decimated data as is illustrated in FIG. 5 (top) as “to touch detector 11”, or data computed therefrom.
  • Such a minimum report rate typically is independent of how the reported data is acquired and processed, that is, it is, for example, independent of the carrier frequency. But the minimum report rate sets the upper limit for the measurement time to the inverse of the minimum report rate.
  • Another requirement for capacitive touch sensing system 21 may be a minimum SNR, or in other words that the expected noise power of an output value is below a limit. In some embodiments, this may even be the primary requirement, and when it cannot be fulfilled with a desired report rate, then the report rate is reduced (i.e., the scan is time increased) while maintaining - and trying to meet - the noise power limitation, as is discussed in the following with reference to FIGS. 8A and 8B.
  • FIGS. 8 A and 8B show a flow diagram of the operation of sensor circuit 1 in another exemplary embodiment.
  • the operation corresponds to the preceding discussion, in particular referring to FIG. 6. Accordingly, the operation in steps 80 - 87 corresponds to the respective operation in steps 60-67, except for steps 82a and 86a - 86g, as discussed in the following.
  • the sensor receive signal, obtained from the capacitive touch sensing system 21 is A/D converted to obtain the digital receive signal, which corresponds to the processing, discussed in the preceding with reference to steps 32 and 62.
  • the sensor receive signal obtained during step 81 has a maximum predefined scan time, i.e., a predefined maximum duration.
  • the predefined maximum duration may be 200 microseconds.
  • step 82a a copy of the digital receive signal with the maximum scan time is stored in memory 10. Then, a portion of the digital receive signal, namely with a predefined minimum scan time, is selected. The further processing of steps 83 - 85 is based on this portion of the digital receive signal.
  • step 86 the acquisition configuration is selected from the candidate acquisition configurations. For clarity, the processing in step 86 is shown in FIG. 8B broken down in steps 86a - 86g.
  • step 86d the configuration circuit 9 increases the scan time by approximately an integer multiple and evaluates this increased scan time.
  • configuration circuit 9 in step 86e obtains the copy of the original digital receive signal with the maximum scan time from memory 10, which was stored in step 82a.
  • a larger portion of original digital receive signal is selected in step 86f, having a scan time that is an integer multiple of the previous scan time, e.g. double the scan time of the preceding portion that was evaluated.
  • the processing then is continued in step 83 and the increased scan time is evaluated according to steps 83-86, as discussed before.
  • the Noise Robustness Level is used herein as an index for a predefined maximum scan or measurement time.
  • step 86d leads to the generation of a warning signal at output 12 in step 86g, warning that no suitable acquisition configuration was found.
  • step 86c uses the AC yielding the best noise measure for operation in the SN-scan.
  • a scan cycle may consist of a noise scan followed by an SN-scan using the AC which yielded the best noise measure. Then follows the next scan cycle with the next noise scan and SN-scan. The scan cycle then is repeated until the device is shut down.
  • the goal is to find the lowest NRL, i.e., the shortest required scan time and thus highest report rate, for which there is a candidate acquisition configuration yielding an ENPE of at most the noise threshold.
  • the process of FIGS. 8A and 8B selects the AC yielding the lowest ENPE.
  • noise scan frequencies can be evaluated in an according embodiment.
  • the j- th decimation rate for the i-th candidate base frequency is denoted as and its corresponding candidate carrier frequency and coefficient vector are denoted as and respectively.
  • step 100 begins in step 100 with the initialization of sensor circuit 1.
  • an individual noise scan is conducted in steps 101, 102, and 103.
  • the present embodiment is not limited to the conduction of three subsequent noise scans.
  • the operation during each of the noise scans corresponds to one of the embodiments, discussed in the preceding with reference to FIGS. 1-9.
  • a noise measure for at least one candidate AC is obtained.
  • noise measures for the same candidate AC may be obtained in a multitude of steps 101, 102, and 103.
  • step 104 an overall acquisition configuration is determined from the candidate acquisition configurations evaluated in the steps 101, 102, and 103.
  • the overall acquisition configuration is determined by selecting the candidate acquisition configuration of steps 101, 102, and 103 for which the lowest ENPE is yielded overall.
  • the overall acquisition configuration corresponds to the best possible candidate acquisition configuration of the noise scans 101, 102, 103.
  • the idea of NRLs can also be applied for this case of multiple noise scan frequencies.
  • step 105 the sensor system is operated in an SN-scan using the overall acquisition configuration. The operation then reverts to step 100 until the processing of sensor circuit 1 is stopped.
  • the approach as described according to the various embodiments not only provides a solution for identifying a relatively best carrier frequency, but a complete solution for noise robustness. It even yields robustness to, for example, AM noise and square noise. This is possible due to the highly accurate, quantitative SNR or noise power estimates which can be computed from the same measurement data but for different ACs. This further allows for finding a trade-off between touch report rate and output SNR.
  • many of the candidate ACs’ parameters can be derived from few high-level requirements (such as, e.g., a 200us scan time), allowing for a simple noise robustness configuration without the need for intense training.
  • a further exemplary aspect of this disclosure relates to obtaining decoupled copies of electric currents as well as digital processing for signal acquisition with overlapping aperture windows.
  • the time duration for which the analog signal is input to the measurement system i.e., the time during which the measurement system is exposed to the outside world and thus its internal analog state is changed by the analog input signal, and can affect the output sample’s value.
  • FIG. 7 shows the magnitude of an ideal ADC’s transfer function, also referred to as susceptibility to single-tone signals with frequency f n , for aperture times 0.833us and 2.5us.
  • susceptibility to single-tone signals with frequency f n for aperture times 0.833us and 2.5us.
  • FIG. 11 A basic exemplary diagram for charge measurement using current integration is shown in FIG. 11. It shows an unknown current source generating current i in which is integrated on capacitor C int while the aperture switch controlled with the signal s ap (t) illustrated in the right-hand side of the figure is on and the reset switch controlled with the signal s res (t) is off.
  • the resistor R of the current source is negligible when the aperture switch is on.
  • the aperture time typically cannot be longer than the time between two successive samples, the sample interval, because the aperture time windows of two successive samples cannot overlap.
  • the higher the sampling frequency the shorter the sample interval and thus the shorter the maximum aperture time.
  • two different types of measurements where the sampling frequency of the first type is a multiple of the sampling frequency of the second type is described, namely the ‘noise scan’ and the ‘SN scan’, yet the same aperture time is desired for both. While the aperture time is chosen for the SN scan, the sampling frequency for the noise scan may be too high to fit an aperture window of the chosen time between two successive samples - the aperture windows would overlap.
  • some means of parallel processing may be beneficial.
  • two or more integrators would be beneficial.
  • a problem may be the risk that these two or more integrators, when tapping the same pad or measurement node, may potentially mutually interfere their measurements. This is illustrated in FIG 12, where on the right-hand side the states and of the aperture switches are plotted over time. During the time when both aperture switches are on, the unknown input current is split uncontrolled between the two integrators. Hence, deterministic measurement with overlapping aperture time windows may not be possible. The same analog input current cannot be measured multiple times this way without the measurements interfering each other.
  • a desired aperture time may, e.g., depend on the sensor type at hand. For example, signal settling times are typically higher for ITO sensors than for PCB sensors due to the lower conductivity of ITO compared to copper. Therefore, a longer aperture time may be desired for an ITO sensor compared to a similarly shaped PCB sensor.
  • a solution may be to employ a current amplifier with one input and multiple outputs to yield a multitude of decoupled copies of the input current. Each copy may then be tapped with one integrator, and the integrator input currents are decoupled, i.e., mutually independent. In a digital post-processing step, the data obtained from the multitude of analog copies may, e.g., be rearranged to yield a single digital output signal.
  • the principle approach of the present discussion is to create multiple decoupled copies of an analog input signal. Then, analog processing and A/D conversion may be performed for each of the signal copies individually. The final step is to interleave, or multiplex, the digital samples from the different processing branches into a single output signal.
  • a standard electronic component where an input current is independent from an output current is a transistor. For more complex components like amplifiers which can contain such transistors, this independence holds too. When an input current controls two output currents, and the input current is independent of either output current, this implies that the output currents are mutually independent from each other too.
  • the analog input signal is an electric current.
  • Some existing touchscreen controller’s analog front end (AFE) provides multiple, essentially identical parallel units for analog processing which are called slices. Each slice comprises an integrator.
  • FIG. 13 schematically shows two of the so-called slices of an exemplary AFE of a touchscreen controller.
  • the pad of the main slice in the top left of FIG. 13 is connected to the input X of a current amplifier.
  • a non-inverting output Z0 of this current amplifier is connected to an integrator whose output is connected to an ADC.
  • An inverting output Z1 of the main slice’s current amplifier is connected to the input of an integrator on a secondary slice, again followed by an ADC.
  • the second slice’s current amplifier is disconnected such that only the main slice’s amplifier inverted current is input to the integrator. While the aperture switches INTMOE can be controlled independently for main and secondary slice, the integrator reset switches RST1 and RST 2 may not be controllable independently.
  • each integration window is preceded by a reset of the integration capacitor.
  • the integration windows of the main and secondary slice are interleaved and overlapping in time.
  • A/D analog-to-digital
  • the samples from the two slices are interleaved to yield a single digital signal.
  • the new single digital signal is created by concatenating the first output sample from the main slice, the first output sample from the secondary slice, the second sample from the main slice, the second sample from the secondary slice, and so on. Note that in the context of a noise scan, the obtained signal is decimated before further processing, and after decimation the current integration windows corresponding to successive samples in these decimated signals are no longer overlapping.
  • FIG. 14 may be not realizable with some touchscreen controller devices because of an integrator reset control which is common for main and secondary slices.
  • A/D conversion also is conducted synchronously on the main and secondary slices, as indicated by vertical dashed lines, such that every other digital sample from each slice is undesired - because it is acquired not at the end of the current integrators’ integration phase but during a possibly random integrator state - and thus may be discarded.
  • FIG. 16 Data obtained with a test implementation using the timing configuration of FIG. 15 is shown in FIG. 16.
  • a single-tone signal with 20kHz is coupled into a sensor electrode connected to a slice Y34, and the sampling frequency is 200kHz.
  • the samples from the main slice Y34 and a secondary slice Y35 are shown in an interleaved manner, while the solid and dashed lines connect the samples from each slice, respectively. It can be observed that the signal of slice Y35 (dashed line) still needs to be re-inverted and shifted, as the signal for Y35 is approximately a mirror image of the signal for Y34 mirrored at the level of ADC value -15.
  • a linear distortion of the input signal i.e., the input current
  • digital equalization i.e., compensation of the distortion
  • a more or less linear copying function can be beneficial, for example, when considering signal equalization together with ADC quantization noise.
  • the preceding touchscreen controller specific solution allows for overlapping aperture time windows when the acquisition frequency on main and secondary slices are the same but only the acquisition phase differs.
  • hardware control would allow fully independent timing for different slices, given multiple copies of the same analog signal, it would be possible to yield a generic solution to the problem of signal acquisition for noise level evaluation with different AFE configurations, including arbitrary different sampling frequencies and aperture time windows.
  • the copy yi(t) is a strictly monotonic function of x(t).
  • the sensor system is a capacitive sensing system.
  • the signal x(t) is an electric current.
  • the signal y(t) is an electric current.
  • two or more analog signal copies yi(t) are input to an analog circuit Hi for generating digital samples and the aperture windows of at least two circuits Hi overlap in time.
  • the analog circuits Hi comprise an integrator.
  • the sampling frequency on two or more circuits Hi is the same.
  • the sensor system comprises a current amplifier whose input is fed with x(t) and where the current amplifier has two or more output stages sharing one input stage.
  • samples from signals on different branches are multiplexed yielding a single output signal.
  • the aperture time is increased beyond the sampling period, thus allowing a highly accurate noise power estimation.
  • Any suitable programming language can be used to implement the routines, methods or programs of embodiments of the invention described herein, including C, C++, Java, assembly language, without limitation.
  • Different programming techniques can be employed such as procedural or object oriented.
  • Any particular routine can execute on a single computer processing device or multiple computer processing devices, a single computer processor or multiple computer processors.
  • Data may be stored in a single storage medium or distributed through multiple storage mediums, and may reside in a single database or multiple databases (or other data storage techniques).
  • sequence of operations described herein can be interrupted, suspended, or otherwise controlled by another process, such as an operating system, kernel, etc.
  • the routines can operate in an operating system environment or as stand-alone routines. Functions, routines, methods, steps and operations described herein can be performed in hardware, software, firmware or any combination thereof.
  • Embodiments described herein can be implemented in the form of control logic in software or hardware or a combination of both.
  • the control logic may be stored in an information storage medium, such as a computer-readable medium, as a plurality of instructions adapted to direct an information processing device to perform a set of steps disclosed in the various embodiments.
  • an information storage medium such as a computer-readable medium
  • a person of ordinary skill in the art will appreciate other ways and/or methods to implement the invention.
  • any of the steps, operations, methods, routines or portions thereof described herein where such software programming or code can be stored in a computer- readable medium and can be operated on by a processor to permit a computer to perform any of the steps, operations, methods, routines or portions thereof described herein.
  • the invention may be implemented by using software programming or code in one or more general purpose digital computers, by using application specific integrated circuits, programmable logic devices, field programmable gate arrays, and so on. Optical, chemical, biological, quantum or nanoengineered systems, components and mechanisms may be used.
  • the functions of the invention can be achieved by any means as is known in the art. For example, distributed, or networked systems, components and circuits can be used. In another example, communication or transfer (or otherwise moving from one place to another) of data may be wired, wireless, or by any other means.
  • a "computer-readable medium” may be any medium that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, system or device.
  • the computer readable medium can be, by way of example only but not by limitation, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, system, device, propagation medium, or computer memory.
  • Such computer-readable medium shall generally be machine readable and include software programming or code that can be human readable (e.g., source code) or machine readable (e.g., object code).
  • non-transitory computer-readable media can include random access memories, read-only memories, hard drives, data cartridges, magnetic tapes, floppy diskettes, flash memory drives, optical data storage devices, compact- disc read-only memories, and other appropriate computer memories and data storage devices.
  • some or all of the software components may reside on a single server computer or on any combination of separate server computers.
  • a computer program product implementing an embodiment disclosed herein may comprise one or more non-transitory computer readable media storing computer instructions translatable by one or more processors in a computing environment.
  • a “processor” includes any, hardware system, mechanism or component that processes data, signals or other information.
  • a processor can include a system with a general-purpose central processing unit, multiple processing units, dedicated circuitry for achieving functionality, or other systems. Processing need not be limited to a geographic location, or have temporal limitations. For example, a processor can perform its functions in "real-time,” “offline,” in a “batch mode,” etc. Portions of processing can be performed at different times and at different locations, by different (or the same) processing systems.
  • ком ⁇ онент may be a process, a process executing on a processor, or a processor.
  • a functionality, component or system may be localized on a single device or distributed across several devices.
  • the described subject matter may be implemented as an apparatus, a method, or article of manufacture using standard programming or engineering techniques to produce software, firmware, hardware, or any combination thereof to control one or more computing devices.
  • the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having,” or any other variation thereof, are intended to cover a non-exclusive inclusion.
  • a process, product, article, or apparatus that comprises a list of elements is not necessarily limited only those elements but may include other elements not expressly listed or inherent to such process, process, article, or apparatus.
  • the term “exemplary” used throughout the specification means “serving as an example, instance, or exemplification” and does not mean “preferred” or “having advantages” over other embodiments.
  • a computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems. Any reference signs in the claims should not be construed as limiting the scope.

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Abstract

Des systèmes et des procédés permettant de déterminer une configuration d'acquisition robuste au bruit pour un capteur ou un système de communication sont divulgués. Un procédé donné à titre d'exemple comprend un balayage de bruit consistant : à obtenir un signal de réception de capteur à partir du système de capteur ; à déterminer un signal de réception numérique à partir du signal de réception de capteur par conversion A/N du signal de réception de capteur à une fréquence de balayage de bruit prédéfinie ; à déterminer une pluralité de signaux de réception numériques décimés par une décimation entière du signal de réception numérique à l'aide de deux taux de décimation ou plus qui diffèrent les uns des autres, chacun desdits taux de décimation étant associé à une configuration d'acquisition candidate respective ; à déterminer une ou plusieurs mesures de bruit pour de multiples des configurations d'acquisition candidates à l'aide d'un ou de plusieurs signaux de la pluralité de signaux de réception numériques décimés ; et à l'aide de la ou des mesures de bruit, à déterminer la configuration d'acquisition correspondant au fonctionnement du système de capteur à partir des configurations d'acquisition candidates.
PCT/US2021/022950 2020-12-16 2021-03-18 Procédés et systèmes permettant de déterminer une configuration d'acquisition robuste au bruit pour faire fonctionner un système de capteur WO2022132212A1 (fr)

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JP2023511993A JP2023549624A (ja) 2020-12-16 2021-03-18 センサシステムを動作させるためのノイズロバスト獲得構成を決定するための方法及びシステム
CN202180059113.7A CN116134407A (zh) 2020-12-16 2021-03-18 用于确定操作传感器系统的噪声稳健性采集配置的方法和系统
DE112021006476.2T DE112021006476T5 (de) 2020-12-16 2021-03-18 Verfahren und systeme zur bestimmung einer rauscharmen erfassungsanordnung für den betrieb eines sensorsystems
KR1020237003331A KR20230117095A (ko) 2020-12-16 2021-03-18 센서 시스템을 동작시키기 위한 잡음에 강건한 취득 구성을 결정하기 위한 방법들 및 시스템들

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US63/126,137 2020-12-16
US17/198,860 US11916582B2 (en) 2020-12-16 2021-03-11 Methods and systems for determining a noise-robust acquisition configuration for operating a sensor system
US17/198,860 2021-03-11

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