Location or movement sensing systems

Abstract

Position or movement sensing system. The present disclosure relates to a sensor comprising a resonant circuit, a driver, a drive enable circuit, a sample and hold circuit, and a measurement circuit. The resonant circuit comprises a passive load and an active circuit, and is tuned so that at least one of the active circuit and the passive load resonates at a resonant frequency. The driver is configured to drive the active circuit to output an RF signal at the resonant frequency, while the drive enable circuit generates a control signal to enable and disable the driver. The sample and hold circuit is configured to hold a peak level of the amplitude signal, and the measurement circuit detects a relative position and / or relative movement between the passive load and the active circuit based on the held peak level. Corresponding systems, methods and apparatus are also described.

Description

[Technical field]

[0001] The present invention relates to a sensor, a system comprising multiple sensors, and a method for detecting the position or movement, in some embodiments, for example, detecting the velocity or movement of a key on a musical keyboard or a key on a computer keyboard. [Background technology]

[0002] The applicant has previously described a resonant circuit based sensor in GB 2494230 and a keyboard sensor system in GB 2570533. More generally, reference is made to the specifications of GB 1115184.2 (GB 2494183), GB 1721448.7 (GB 2569578), GB 1812826.4 (GB 2570533), GB 1909213.9 (GB 2576610), GB 1909214.7 (GB 2578346), GB 2017797.8 and GB 1208162.6 (GB 2494230).

[0003] Resonant sensors that employ induction coils for sensing, particularly position sensors and sensing systems, have many use cases due to their reliability, precision, accuracy, and low cost. However, such sensing systems are not suitable for many applications because the power required to drive the sensor's induction coil may be too high. For example, high power is a disadvantage in systems that require wireless connectivity and / or battery power.

[0004] Furthermore, induction coils are typically excited by high frequency drive signals, e.g., frequencies above 1 MHz. This drive signal is often composed of a fundamental frequency and harmonic frequencies that can extend to tens or hundreds of MHz, causing undesirable electromagnetic radiation that can interfere with other systems. Thus, resonant sensors known in the art may be disadvantageous or unsuitable for any system that requires low levels of electromagnetic interference (EMI), such as, for example, a high precision position sensor where it is desirable to accurately calculate velocity.

[0005] To reduce unwanted electromagnetic emissions and / or EMI, one could consider employing a sinusoidal drive signal that does not contain harmonic frequencies, but this could add additional cost, complexity, and does not address the issue of high power requirements.

[0006] Systems that include a large number of resonant position sensors, especially those that operate simultaneously, further increase power requirements and undesirable electromagnetic emissions. For example, 88 position sensors may be required to sense the position of a key on a musical (piano) keyboard, or 104 or more position sensors may be required to sense the position of a key on a computer keyboard. Reducing power consumption in computer keyboards is further advantageous, since computer keyboards are often wireless for the convenience of the user, and thus require a local battery supply.

[0007] It is therefore desirable to provide a position and / or movement sensing system that employs inductive sensing techniques and that, in particular, has reduced power requirements and EMI emissions, greater accuracy, more repeatable sensor output, and / or faster sensor speeds, for example to enable faster scanning speeds. Summary of the Invention

[0008] According to one aspect, a sensor is provided that includes a resonant circuit including a passive load and an active circuit, where at least one of the active circuit and the passive load is tuned to resonate at a resonant frequency, a driver that drives the active circuit to output an RF signal at the resonant frequency, a drive enable circuit that generates control signals for enabling and disabling the driver, and a sample and hold circuit for an amplitude signal indicative of the amplitude of the RF signal output from either the passive load or the active circuit, where the sample and hold circuit holds a peak level of the amplitude signal during a period when the driver is enabled. The sensor further includes a measurement circuit for detecting a relative position and / or relative movement between the passive load and the active circuit based on the held peak level, the measurement circuit performing the detection by measuring the held peak level when the driver is disabled by the drive enable circuit.

[0009] The active circuit and / or the passive load may comprise an induction coil integrated into a tuning electronic circuit, the tuning electronic circuit having a resonant frequency f R Thus, either or both of the active circuit or the passive load preferably comprise a tuned resonant circuit. Either the active circuit or the passive load may be excited by a drive signal from a driver. In this case, the driver is generally R The active circuit outputs an RF signal at a frequency equal to or close to that of the active circuit. Typically, the passive load (also called the "target") is selected such that the proximity of the passive load element to the active circuit causes a change in state of either the passive load or the active circuit, for example, by changing the resonant frequency and / or quality factor of the tuned circuit, or by the transfer of electrical energy from the active circuit to the target / passive load. The relative position and / or relative movement and / or relative velocity (e.g., speed) of the active circuit and the target can be sensed by detecting such a change, for example, at the resonant condition of the tuned circuit.

[0010] In some examples, the sample and hold circuit may be configured to be effectively isolated (e.g., by ground) from the driver during the period of detection by the measurement circuit. For example, the sample and hold circuit may have a threshold voltage such that when the input to the sample and hold circuit is below the threshold voltage, the peak level held by the sample and hold circuit is not affected by noise and / or other signals at the input. The sample and hold circuit may be implemented digitally or may be provided with analog circuitry. In either case, advantageously, the driver does not need to remain active / enabled for the measurement circuit to detect the relative position and / or relative movement within the sensor. In this way, the sampling circuit may hold the peak amplitude from the time the active circuit was driven. Thus, the relative position or relative movement may be indirectly detected / measured after the driver is disabled. This may reduce the power required for sensing. Additionally or alternatively, the system may allow for reduced electromagnetic interference (EMI) since the sensor driver does not need to be active during sensing.

[0011] In general, the measurement circuit may detect variations in a resonant signal output by an active circuit or a passive load to determine the relative position and / or movement of the active circuit and the passive load.

[0012] The driver's control signal may preferably (i.e., optionally) be configured or timed to repeatedly and / or periodically enable and disable the driver so that the driver does not drive the active circuitry simultaneously with measurement / detection by the measurement circuitry.

[0013] In some implementations, the measurement circuitry may detect the relative velocity between the passive load and the active circuitry. In this regard, multiple successive relative positions may be detected to determine / calculate the relative velocity between the active circuitry and the passive load.

[0014] In some implementations, the sample and hold circuit comprises a peak detect input circuit configured to perform amplitude sensitive demodulation to generate an amplitude signal. Additionally, the peak detect input circuit may comprise a diode configured to charge a capacitor to generate a voltage corresponding to the peak level. Advantageously, the diode may provide additional protection from electrical or EMI noise.

[0015] In any of the embodiments disclosed above, the sample and hold circuit may further receive an input signal responsive to the RF signal from either a passive load or an active circuit, and generate an amplitude signal based on the input signal when the input signal exceeds a threshold voltage.

[0016] Such a configuration has the added advantage that if the sample and hold circuit is effectively isolated from the driver, then EMI may be further reduced, regardless of the state of the driver, since the sample and hold circuit may be effectively grounded from any input signal.

[0017] In some implementations, the driver may drive the active circuit with a predetermined number of RF pulses during the period the driver is enabled. The driver's drive signal may be a series of pulses, for example a pulse train, such as a square wave or a sine wave. In general, the pulse train may have any duty cycle, but approximately 50% is preferred to provide a good balance between power consumption and efficiency in resonating either the passive load or the active circuit.

[0018] In general, the sample and hold circuitry reaches a peak level and / or a steady state in response to a certain number of pulses. Thus, the number of pulses may be selected to be sufficient to achieve said steady state / maximum value. After achieving this steady state, the driver may be disabled. Thus, the driver may be actively driven only for a time sufficient for the sampling circuitry to reach a steady state. That is, the drive signal does not need to be continuously active and / or the period during which the drive signal is enabled may be precisely controlled, thereby significantly reducing power consumption.

[0019] In any of the above sensor embodiments, the driver may include a counter that counts the RF pulses, and the drive enable circuit may be configured to disable the driver when the count reaches a predetermined number. This allows for inherent synchronicity; that is, by counting the number of RF pulses, the drive signal is repeatable, and therefore the resonant response from either the active circuit or the passive load is also generally repeatable. This allows for more accurate and / or reliable position and / or movement detection.

[0020] In some implementations, the sample and hold circuit may be configured to be reset after the measurement and before the next re-enabling of the driver by the drive enable circuit, allowing the previously held peak level of the amplitude signal to be immediately reset, for example by discharging a capacitive element, so that further peak levels can be sampled after further enabling of the drive signal.

[0021] Alternatively, in embodiments without a reset function, the sample and hold circuit may decay (e.g., exponentially) the held peak level signal. The measurement circuit may perform detection during this decay period. In such an example, no reset switch is required. In some implementations, the measurement circuit performs measurements after a settling period during which the driver is disabled.

[0022] The presence of a quiet or waiting period allows any residual noise or RF frequencies, e.g. from the driver, active circuitry or passive load, to dissipate before being detected by the measurement circuitry, thus improving the reliability and / or accuracy of the measurement by reducing errors that would otherwise be caused by EMI noise.

[0023] According to a further aspect, there is provided a system comprising a multiplexer that allows multiple resonant circuits to be driven simultaneously or at different times, preferably sequentially, and allows each measurement circuit to perform a measurement during a period when the driver is disabled from driving each active circuit. The system may be configured such that each measurement circuit can perform a measurement simultaneously during a period when the driver is disabled from driving each active circuit.

[0024] Thus, when all of the active resonators are disabled, multiple measurements can be performed simultaneously. In some embodiments, this allows for faster scanning speeds of multiple sensors controlled by a multiplexer. This is useful, for example, in musical keyboards with 88 keys and / or computer keyboards with over 100 keys, where high scanning speeds are typically desired.

[0025] Further advantageously, the sample and hold circuits can be configured to hold peak levels so that the drivers do not need to be continuously active, so that multiple sensors can be driven in parallel, e.g., exactly in phase or slightly out of phase. That is, measurement circuit detection for multiple sample and hold circuits can be obtained in the same measurement slot. This is in contrast to measuring one sensor per measurement cycle or measurement time slot, e.g., driving an active circuit and then performing measurement circuit detection one sensor at a time (which is generally less efficient).

[0026] Thus, detection of relative position and / or relative movement can be performed simultaneously or sequentially for multiple sensors, preferably with each detection performed during a period when all driver(s) of the active circuitry are disabled, and detection by each measurement circuit of multiple sensors can occur within a single measurement cycle, allowing faster scanning speeds in multiplexed systems.

[0027] According to a further related aspect, there is provided an apparatus which is a musical instrument keyboard, a computer keyboard, a computer touchpad, preferably a musical instrument foot pedal, or a drum, comprising at least one sensor according to the sensors described above, or preferably comprising an embodiment of the system as described above, wherein the musical instrument is an electronic or acoustic piano, organ, guitar, or drum.

[0028] In some implementations, the passive load may comprise a resonant circuit configured to resonate at a resonant frequency when the active circuit is driven by the driver, In such implementations, the active circuit may comprise a resonant circuit configured to resonate at a frequency different from the resonant frequency.

[0029] Alternatively, in some embodiments, the passive load may be a conductive target.

[0030] In some embodiments having any of the above-mentioned passive loads, the active circuit may be a resonant circuit configured to resonate at a resonant frequency. For example, both the passive circuit and the active circuit may be tuned resonant circuits. For example, the tuned resonant circuits may optionally be multiple induction coils, each of which includes two smaller primary coils with counter-winding directions arranged in series to form a figure-eight coil.

[0031] In some embodiments, the sample and hold circuit is coupled to the output of the active circuit and configured to indicate the amplitude of the RF signal output from the active circuit. In other embodiments, the sample and hold circuit may be connected to the output of the passive load and configured to indicate the amplitude of the RF signal output from the output of the passive load. In other words, the RF signal output of either the active circuit or the passive load can be sampled and measured to determine the relative separation between the active circuit and the passive load.

[0032] A configuration in which the passive load is a conductive target, such as, for example, a metal object without a resonant coil, may be beneficial, for example, when only very small changes in position need to be detected and / or when the target / passive load may be very close to active circuitry, for example, in a computer touchpad. In such an example, the passive load is a conductive finger pad that deflects in response to a touch, and the amount of deflection is measured by a sensor. Furthermore, with multiple active sensors responsive to the deflection of the conductive finger pad, the location of the touch can be determined by interpolation of the measured position output of each of the multiple active sensors. [Brief description of the drawings]

[0033] The above and other aspects of the invention are further described below with reference to the accompanying drawings. [Figure 1] FIG. 1 shows a block diagram of an inductive position sensing system known in the art. [Diagram 2] FIG. 2 shows an example of an electronic circuit for use as the active circuit of an inductive position sensor. [Diagram 3] FIG. 3 shows an example of an electronic circuit for use as a passive target in an inductive sensing system. [Figure 4] FIG. 4 shows an example of a phase sensitive detector for detecting the output of an active circuit or a passive load in an inductive position sensing system. [Diagram 5] FIG. 5 shows an example of an amplitude sensitive demodulator for detecting the output of an active circuit or passive load in an inductive position sensing system. [Figure 6a] FIG. 6a shows a close-up of an example PCB design as an embodiment of a tuned resonant circuit for an active circuit. [Figure 6b] FIG. 6b shows a close-up of an example PCB design as an embodiment of a tuned resonant circuit for a passive load. [Figure 7] 7 shows a cross-sectional view of a key of a musical keyboard, the position of which is determined using an exemplary embodiment of the system. [Figure 8] FIG. 8 shows an example of a timing diagram of a measurement process with a continuous drive signal for a single position sensor equipped with the circuit according to FIG. [Figure 9] FIG. 9 illustrates a block diagram of an inductive position sensing system according to one embodiment. [Figure 10] An example of a sample and hold electronic circuit is shown in FIG. [Figure 11] FIG. 11 shows an example of an electronic circuit that combines amplitude sensitive demodulation with a sample-and-hold function. [Figure 12] FIG. 12 shows a flow chart of a measurement process according to one embodiment. [Figure 13] FIG. 13 shows an example of a timing diagram for the measurement process of a single position sensor. [Figure 14] FIG. 14 shows an example timing diagram of a multiplexing scheme corresponding to multiple measurements of multiple exemplary sensors. [Figure 15a] FIG. 15a shows an example of a voltage scan of a continuous drive signal and the corresponding sensor response. [Figure 15b] FIG. 15b shows an example of a voltage scan of the drive signal and sensor response according to a pulse burst embodiment. [Figure 16a] FIG. 16a shows another example of voltage scans of drive signals, sensor responses, and timing signals according to one embodiment. [Figure 16b] FIG. 16b shows a zoomed-in view of the voltage scan of FIG. 16a. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] FIG. 1 shows a block diagram of a sensing system employing an inductive coil as a position / movement sensing element. The block diagram shows an active circuit as an inductive coil sensor 1 having an output 10 that varies with variations in separation 3 between the coil sensor 1 and a passive load, i.e., target 2. The sensor 1 is driven / excited by a driver 4, which generates a drive signal. The output 10 of the sensor 1 is processed by a detector 5 (also called a measurement circuit). FIG. 1 shows that a measurement circuit 6 is used to generate a value representative of, or dependent on, the separation between the sensor 1 and the target 2. In general, the position of either the sensor 1 or the target 2 with respect to the other can be measured. Alternatively or additionally, the relative movement and / or relative velocity of the sensor 1 and / or the target 2 can be measured.

[0035] Figure 2 shows an active circuit for a sensor 1 for use in the sensing system of Figure 1. The sensor 1 comprises a sensor induction coil 7, one or more capacitive elements 8 which form a resonant electronic circuit with the sensor induction coil 7, a drive input 9 to which a suitable drive signal is applied, and an output 10 at which the output of the sensor is detected. The resonant electronic circuit can be adjusted to a resonant frequency f by selecting or tuning the capacitance of the capacitive element 8 and / or the inductance of the sensor induction coil 7. R A suitable time-varying drive signal, such as a sine wave or a pulse train (e.g., a square wave), may be tuned to a frequency f RWhen a frequency at or near that is applied to the drive input 9 , the sensed output of the sensor will generally respond according to the proximity of the suitable target 2 .

[0036] FIG. 3 illustrates a tuned resonant circuit suitable for use as the target 2 in the sensing system of FIG. 1. In general, a suitable target 2 may include or be constructed from any conductive material, such as a metal. The target 2 may be a resonant circuit (optionally a tuned circuit) as shown. A conductive target need not necessarily be a resonant circuit. By way of example only, FIG. 3 illustrates a tuned resonant circuit connected to a target capacitive element 12 to tune the resonant frequency f of an active circuit. R 1 shows a target induction coil 11 which forms a resonant circuit with a resonant frequency that can be tuned to be equal to or close to

[0037] In some instances, the sensor output 10 is not suitable for direct measurement. In such cases, a detector 5, such as that shown in Figure 1, can be used to process and convert the output of the sensor 1 into a form suitable for direct measurement.

[0038] FIG. 4 shows one suitable configuration of such a detector, comprising a signal multiplier 15 connected to the sensor output 10, a reference input 13 connected to a reference signal synchronized to the sensor drive signal, a phase shift element 14 for phase shifting the reference signal, a low pass filter 16 for filtering the output of the signal multiplier 15, and / or an output 17 at which a phase sensitive detector output is obtained.

[0039] Figure 5 shows another example of a suitable detector configuration, which is an amplitude sensitive demodulator. It shows that the sensor output 10 is rectified by a diode 18 which forms a peak hold circuit with a capacitive element 19 and a resistive element 20. The output of the peak hold circuit is shown at output 17. The time constant of the peak hold circuit of Figure 5 can be determined by the capacitance of capacitive element 19 and the resistance of resistive element 20. For example, τ = RC, where R is the resistance of resistive element 20 and C is the capacitance of capacitive element 19.

[0040] In general, however, the peak-hold circuit of FIG. 5 may be driven by a continuous drive signal to allow the detector to measure the output at output 17. It is possible to measure the signal even in the absence of a continuous drive signal, however, the signal from output 17 decays (e.g., exponentially) through resistor 20. Thus, in some examples, a high time constant (e.g., achieved by making resistor 20 high resistance) may be selected to allow the signal to be read from the peak-hold circuit of FIG. 5. This allows the use of a non-continuous drive signal, advantageously saving power. In this regard, in broad terms, it is preferred that the decay time of the RC time constant is long relative to the measurement time. Thus, in some embodiments, errors caused by voltage drops following the disablement of the drive signal will be reduced. However, it is also preferred that the RC decay time is short enough relative to the cycle time so that the held signal can substantially or completely decay before the next measurement.

[0041] In this sense, the circuit of Figure 5 can be considered as an approximation to a sample-and-hold circuit (e.g., as provided in Figure 11) and may achieve lower power. Measurement accuracy may generally be achieved by precisely controlling the time the drive signal is active, e.g., by counting the number of pulses.

[0042] The time constant of the low pass filter 16 in FIG. 4 and / or the time constant of the peak hold circuit in FIG. 5 are determined by the f RThe time constant may be selected to be large enough to reduce (generally to a level acceptable for the sensing system application) the level of frequency components of the sensor drive signal that are equal to or close to . Such frequency components may otherwise introduce errors into the measurement 6. In accordance with the requirements of the sensing system application, the time constant is preferably small enough to react to fast movements of the sensor, for example to be able to detect rapid changes in the separation between the sensor and the target. Thus, in selecting the time constant, there may be a compromise between minimizing measurement errors by reducing the level of frequency components of the sensor drive signal and maximizing the response speed of the sensing system measurement 6.

[0043] The embodiment of the sensing system including the detector of FIG. 4 or FIG. 5 can be improved. For example, if a measurement is performed while the sensor drive signal is active, measurement errors may be directly introduced. Direct errors may occur because frequency components of the sensor drive signal that are not filtered out may cause undesired fluctuations in the sensor measurement. Similarly, a continuously active drive signal may cause indirect errors and / or reduce reliability, for example because variations in circuit voltage and circuit current resulting from the sensor drive signal are coupled into the measurement element, for example by an analog-to-digital converter. In other words, a continuously active drive signal may cause undesired additional electromagnetic interference (EMI).

[0044] Figure 6 shows an example sensor induction coil component that may be used in conjunction with any of the measurement and / or detection circuits of the present disclosure. Figures 6a and 6b show an example of an active tuned resonant circuit including a sensor induction coil 7 driven by a sensor driver 4 and a coil inductor 11 used with a target 2, respectively. Both circuits are printed circuit designs.

[0045] With reference to Fig. 6a, an active tuned resonant circuit may be formed on a printed circuit board including a single conductive layer or multiple conductive layers, in which a coil 1' is formed in a continuous spiral track. Electrical continuity of the track is maintained by electrically connecting it through a connection via 53' to a connection wire or to another spiral track on another conductive layer or to multiple spiral tracks on multiple conductive layers of the printed circuit board. Capacitive elements 2' and 3' (e.g. corresponding to capacitive element 8 in Fig. 2) and resistive elements 4' and 5' are closely arranged. Connection points 6' and 7' are provided for the drive electronics and the readout electronics, respectively.

[0046] Similarly, referring to Figure 6b, the passive tuned resonant circuit (forming target 2) may be formed on a printed circuit board including a single conductive layer or multiple conductive layers, in which a coil 8' is formed in a continuous spiral track. Electrical continuity of the track is maintained by electrically connecting it through connection vias 54' to connecting wires or to other spiral tracks on other conductive layers or to multiple spiral tracks on multiple conductive layers of the printed circuit board. A capacitive element 9' is located proximally.

[0047] In another embodiment, the sensor induction coil 7 of the active circuit can be formed from a number of electrically connected primary minor coils. The winding directions of these primary minor coils are selected so that the sum of the far electromagnetic fields radiated from the primary minor coils is substantially zero. As a particularly preferred but non-limiting example, the induction coil 7 is wired in series with opposite winding directions so that two primary minor coils form a figure-of-eight coil. In such an arrangement, the far electromagnetic fields radiated from the first half of the figure-of-eight coil and the far electromagnetic fields radiated from the second half of the figure-of-eight coil may be equal in magnitude but opposite in polarity. Thus, the far electromagnetic field radiated from the figure-of-eight coil is substantially zero.

[0048] In such an arrangement, the target 2, which is a passively tuned resonant circuit, may be inefficient unless the induction coil of the passively tuned resonant circuit is primarily inductively coupled to only one half of the figure-eight coil of the active tuned resonant circuit. To maximize the output signal of the position sensor, the induction coil of the passively tuned resonant circuit is preferably formed of a figure-eight induction coil as well. The figure-eight induction coil comprises two secondary minor coils wired in series with opposite winding directions. Each secondary minor coil is primarily inductively coupled to a separate primary minor coil of the figure-eight coil of the active circuit.

[0049] Figure 7 shows an embodiment of a resonant sensor in a musical keyboard. The key mechanism sensor comprises a movable top member 15' which rotates about a pivot point 17' and is restrained from movement by a spring 16' or other mechanical linkage, a fixed bottom member 14', a deformable end stop 18' which limits the movement of the top member, and a position sensor. The position sensor comprises an active tuned resonant circuit 10' inductively coupled to an electrically reactive element 11' (hereafter called the target), drive electronics connected to the active tuned resonant circuit, and readout electronics connected to the active tuned resonant circuit. The position sensor outputs a signal which varies with changes in the mutual separation between the active tuned resonant circuit and the target.

[0050] As shown in FIG. 1, generally, the target (e.g., the passive tuned resonant circuit) is not electrically coupled (e.g., not directly wired) to the circuit, and only the output of the active resonant sensor 1 may be measured, where the output varies based on the load on the active resonant sensor due to the proximity of the sensor. However, it may be possible to measure the output of the passive load circuit based on how hard it is driven by the actively driven resonator. In this case, the varying output of the active circuit may be irrelevant, since only the passive circuit needs to be measured. Generally, instead of the sensor output 10 being coupled to the detector 5 in FIG. 1, the output of the target may be directly coupled to the detector 5 (in this case the driver and sensor are conductively isolated from the rest of the system).

[0051] Furthermore, in some instances, only the passive circuitry may have a tuned resonance, and the active circuitry may not be tuned to a resonant frequency. In this regard, the active circuitry may be a non-tuned transmit coil, in which case the passive circuitry is a receive coil that is tuned to resonate at the frequency of the drive signal. In summary, at least the following circuit combinations are possible for use as resonant sensors in the measurement schemes disclosed herein: When the output of an active circuit is measured, i. the sensor 1 is a resonant active circuit and the target 2 is a conductive (metallic) target, or ii. The sensor 1 is a resonating active circuit and the target 2 is a resonating passive circuit. When the output of a passive circuit is measured: iii. the sensor 1 is a resonant active circuit and the target 2 is a resonant passive circuit, or iv. The sensor 1 is a non-resonant (untuned) active circuit and the target 2 is a resonant passive circuit.

[0052] FIG. 8 shows an example of a timing diagram illustrating a method of driving and measuring a sensor compatible with the circuit of FIG. 4 or FIG. 5. As mentioned above, a continuous drive signal 38 can be used. The timing diagram shows that the sensor drive signal 38 is enabled 29, and after an (optional) initial pause period 39 (e.g., allowing signal 43 to stabilize), a continuous series of pulses is applied to the sensor, causing the detection output 43 from the sensor to approach a value representing the detection separation between the sensor and the target. This detection output value may include frequency components of the drive signal 38. The amplitude of the frequency components depends on the time constant of the filtering applied in the detector (not shown) that generates the detection output. The drive signal shown is a square wave, but any pulse train (e.g., having a duty cycle other than 50%) or a sinusoidal drive signal may also be suitably employed. A measurement 42 is made during a period 40, where the measurement may include additional filtering or processing to reduce the amplitude of the frequency components of the drive signal.

[0053] Thus, there may be a trade-off between the speed of the measurement and the amount of removal of frequency components of the drive signal. For example, a higher time constant may reduce undesirable frequency components in the drive signal, but may require a longer pause period. Optionally, the second measurement may be performed after a period 41 has elapsed following completion of the first measurement (and thus the period 41 may be zero).

[0054] Referring again to FIG. 5, the aforementioned direct and indirect errors can be reduced by employing long time constants in the detector, but this can slow down the response speed. This is undesirable, for example, when high scanning speeds of the sensor are required. Furthermore, increasing the time that the sensor drive signal is active (e.g., with a continuous signal) can increase the total power required by the sensing system, which is undesirable for low power sensing systems. Furthermore, the increased power requirements can result in further increases in the level of electromagnetic radiation emitted by the sensing system at the fundamental and harmonic frequencies of the sensor drive signal, which is generally undesirable.

[0055] It may therefore be advantageous to further improve the peak hold circuit of FIG. 5 and / or the measurement regime of FIG. 8 by providing a system with reduced power requirements and reduced EMI emissions.

[0056] Figure 9 shows a block diagram of an improved detection system. Compared to Figure 1, a sample and hold circuit 27 is interposed between the detector 5 and the measurement circuit 6, and a control unit 28 is added to control the sensor drive signal 4, the sample and hold circuit 27, and the measurement circuit 6. The peak hold circuit of Figure 5 is suitable for use as the sample and hold circuit 27 in some instances, for example where a large time constant exists.

[0057] FIG. 10 shows a sample and hold circuit 27 suitable for use in an improved embodiment of the system of FIG. 9. The sample and hold circuit 27 comprises an input 21, a sample / hold switch 22, a voltage storage capacitive element 23, an optional signal buffer 24 and / or an output 25. When operating in a sampling mode (e.g. when sampling a signal presented at the input 21), the switch 22 is closed so that the voltage storage capacitive element 23 charges or discharges towards a voltage level corresponding to the (peak) voltage of the input 21. When the sample and hold circuit operates in a hold mode, the sample / hold switch 22 is opened, allowing the capacitive element 23 to maintain the charged or discharged sampled voltage during sampling. Advantageously, such a circuit can maintain the sampled peak signal even in the absence of an active signal, allowing a non-continuous signal drive. This may generally allow significant power savings and / or reduced EMI.

[0058] Preferably, a high impedance circuit path is provided on the active side (ungrounded side) of the voltage storage capacitive element 23 to ensure that the sampled voltage is maintained during the hold period. This may be achieved by ensuring that the sample / hold switch has a high impedance in the off state, and optionally by connecting the output 25 to a high impedance measurement device and / or adding a signal buffer 24 to isolate the voltage storage capacitive element 23 from the impedance of the measurement device. In addition, providing a high impedance circuit path on the active side of the capacitive element 23 prevents conducted electrical noise, thus allowing the sampled voltage to be maintained more stable.

[0059] FIG. 11 shows a further improved sample-and-hold circuit and a resettable peak detector for use in the system of FIG. 9. This has the advantage of performing amplitude-sensitive demodulation (for example, as described with reference to FIG. 5) without the need for a resistive element 20. The sample-and-hold circuit can therefore be considered to have a practically "infinite" time constant. The sample-and-hold circuit of FIG. 11 therefore has the advantage that there is no physical time constant. This allows for an effective execution of the sample-and-hold operation while avoiding the need to compromise between the removal of undesirable frequency components in the drive signal and the sensor speed. Surprisingly, therefore, a resonant sensor with such a sample-and-hold circuit can achieve all three of the following: increased drive speed, reduced EMI emissions, and / or reduced power.

[0060] The resettable peak detector may comprise a connection to the sensor output 10, a diode 18 to allow charging of a capacitive element 19 with the voltage at the sensor output, a reset switch 26 to discharge the capacitive element, and / or an output 25 connected to a measurement device. Optionally, a signal buffer 24 may be provided to isolate the capacitive element 19 from the impedance of the measurement device. Sampling may be performed when the reset switch 26 is open and the sensor drive signal is active, providing a signal at the sensor output 10. The capacitive element 19 is configured to detect when the voltage at the sensor output 10 exceeds a threshold voltage V th =V C +V D When the voltage exceeds V C is the voltage stored in the capacitive element 19, and V D is the voltage drop across the diode 18. Hold occurs when the voltage at the sensor input 10 drops below the threshold voltage V thbelow 1 V. However, capacitive element 19 is not allowed to back discharge through diode 18. To perform a new sample-and-hold operation to measure a new sensor-to-target separation, capacitive element 19 may be discharged by closing reset switch 26, preferably when the sensor drive signal is inactive / not enabled.

[0061] In a preferred embodiment, and in contrast to FIG. 8, the sensor drive signal is discontinuous. For example, the sensor driver may drive a period of time t drive Only one active drive may be predetermined. For example, an optimal value may be determined during the design of the sensing system or during a calibration process that is performed every hour. drive The period of time may be determined based on the time required for a particular drive signal to drive a resonating sensor in a rest position to a steady state (see, for example, 33a in FIG. 15b).

[0062] In some embodiments, the sensor drive signal comprises a series of pulses (e.g., a pulse train such as a square wave). The interval t between the start times of successive pulses period is 1 / f R The pulse train is set to be equal to or close to the pulse length, and the number of pulses in the train is an integer value. Therefore, the number of pulses in the train is N drive Here,

number

[0063] FIG. 12 shows a flow chart of an exemplary measurement process. It should be understood that the order of steps in the flow chart is not limited to the order shown. For example, steps S100, S102, and S104 can be reordered or, preferably, performed in parallel. In steps S106 and S108, pulses are counted to ensure a repeatable output signal. Preferably, as described below, the phase of the pulse train signal is synchronized with the activation S102 of the drive signal such that an integer number of pulses is provided each time. In step S110, a predetermined pulse count number (e.g., the time t required to output the number of pulses) is determined. drive When the drive signal reaches a peak signal level (corresponding to 100 Hz), the drive signal is disabled. It should further be appreciated that step S112 is particularly optional. For example, in cases where the scanning speed is high, a measurement can be made immediately after the drive signal is disabled. However, in some instances, it may be preferable to provide a pause period during which the drive signal is inactive to further reduce undesired signals and / or undesired EMI from the drive signal. The detection and / or measurement circuit measures the peak signal held in S114, after which the sample and hold circuit is reset in S116 (e.g., by momentarily closing switch 26 in the circuit of FIG. 11).

[0064] Figure 13 shows a timing diagram of an exemplary measurement process corresponding to the flow chart of Figure 12. The process of Figure 13 begins by enabling the output of the sensor drive signal 29 and applying the signal 29 to the sensor as a series of pulses 32. The sample and hold circuit is operable to sample and hold the peak level of the drive signal for a period 37. For example, in the circuit shown in Figure 11, the reset switch 26 is opened to allow the capacitive element 19 to accumulate charge. The detected output 33 from the sensor is generated during the active time t of the series of pulses 32. drive, and is then peak-held by the sample and hold circuit (as shown at the stable value of the detector output 33). It will be appreciated that in general any oscillating drive signal is suitable (e.g., a sine wave, a pulse train with an asymmetric duty cycle, etc.), and that an inverted drive signal (relative to pulse 32) is also possible. In general, any oscillating signal that causes the induction coil of the resonating sensor to resonate is suitable.

[0065] A given number of pulses, N drive After V is applied to the sensor, the sensor output voltage is preferably adjusted to V so that further fluctuations in the sensor output voltage do not affect the voltage held by the sample-and-hold circuit. th 13. The output of the sensor drive signal 29 is disabled (e.g., by a drive enable circuit, or a digital controller) so that the voltage Vcc falls below 1 V. After an optional rest period (e.g., the interval between periods 34 and 35), measurement 30 is initiated to measure the voltage held by the sample and hold circuit, and is performed for period 35. Finally, the sample and hold circuit is reset 31 (e.g., by closing reset switch 26 in the case of the sample and hold circuit of FIG. 11) for period 36. The sampling and measurement process shown in FIG. 13 may then be repeated for subsequent measurements. The time interval between periods 35 and 36 is also arbitrary, and is illustrated only for clarity. For example, the sample and hold circuit may be reset immediately after measurement 35 to provide an advantageously fast scanning speed.

[0066] For the sampling and measurement process of Fig. 13, it is preferable to use a circuit as in Fig. 11. Advantageously, in comparison with the measurement process of Fig. 8, it can be seen that the hold signal 33 of the sample and hold circuit is much more stable than the signal 43 of the peak hold circuit used in Fig. 8. This stability is due to the absence of a drive signal and / or RC time constant used in Fig. 11. This allows for a substantial reduction in EMI noise / errors in the detection output.

[0067] Additionally, it is advantageous for the sensor drive signal 32 (e.g., the phase of the pulse train signal) to be synchronized with the timing of the start and stop 29 of the sensor drive signal (e.g., the enabling and disabling of the drive signal by a drive enable circuit). In this way, the shape and phase of the sensor drive signal 32 will be substantially similar each time the sensor is driven, preferably resulting in a repeatable output from the sensor and detector output 33, which in turn allows measurements to be output from the sensing system with high repeatability and / or low error. Furthermore, such a repeatable signal generally does not require averaging or filtering with long time constants, allowing for faster sensor scan rates. In particular, for a given measurement performance, imposing this synchronicity allows for a faster t than if the sensor drive signals were not synchronized with the start / stop timing of the sensor drive signals. drive can be shortened. drive Reducing the length of the sensing system may advantageously reduce the power requirements of the sensing system and / or allow measurements from the sensing system to be performed more frequently. Thus, embodiments may provide any one or more of faster position change measurements, faster sensor scanning speeds, more accurate sensor velocity measurements, and / or an increased number of sensors that can be effectively scanned in a multiplexed sensor system.

[0068] In some embodiments, an exemplary implementation of the system may multiplex multiple active tuned resonant circuits using a time division multiplexing system (e.g., controlled by a circuit or suitable digital controller) to determine the relative position or relative movement of multiple sensors. A musical keyboard with one sensor per key is an exemplary implementation. In such an implementation, a subset of the position sensors are enabled at any one time. In general, a multiplexing system has the advantage of reducing cost, complexity, power consumption and electromagnetic emissions when a large number of sensors are required.

[0069] Generally, driving multiple (adjacent) sensors simultaneously or sequentially in quick succession generates undesirable EMI and measurement errors. For example, any resonating sensor may be driven by the signal of an adjacent resonating sensor, which may cause problems in accurately measuring the position of the sensor. In this regard, multiplexing systems may generally include one or more mitigation systems to reduce the amount of noise / EMI. Such mitigation methods may include, for example, synchronous demodulating the output of the position sensor to remove interference components, driving adjacent sensors with different resonant frequencies, designing the drive of the multiplexer so as not to drive adjacent or nearby sensors simultaneously, and / or physically offsetting the positions of adjacent sensors from each other. Such systems may add additional complexity to known multiplexing systems. Nevertheless, multiplexing systems have room for substantial improvement in terms of sensor speed. For example, the time response of the low pass filter used in synchronous demodulation may limit the response speed of the position sensor, which is undesirable.

[0070] Advantageously, the sample and hold techniques and implementations of the present disclosure provide a faster multiplexed system that can, for example, efficiently drive and measure multiple sensors in parallel or at much higher speeds in series, preferably without compromising EMI emissions. For example, the circuit of FIG. 11, and in particular the inherent threshold voltage of diode 18, can provide effective electrical isolation between the sampling / detection circuitry and any directly connected or adjacent drive signal / resonating sensor.

[0071] 14 illustrates a timing diagram of a multiplexing scheme according to one embodiment, where a single sensor measurement process (e.g., that of FIG. 13) is applied to multiple sensors. Advantageously, in the illustrated improved multiplexing scheme, each sensor of the multiple sensors is measured at least once within one timeslot N. This is in contrast to multiplexing systems that measure at most one sensor per timeslot.

[0072] Within each time slot, a drive signal 32 is applied as a series of pulses to each sensor of the plurality of sensors. The detector output 33 of each sensor is measured at least once within the valid period 30, and the detector sample-and-hold circuitry is reset 31. Preferably, the timing may be configured such that only a single drive signal of the plurality of drive signals for any sensor of the plurality of sensors is active at any one time. This may provide the advantage of reducing the peak power required by the measurement system, which in turn reduces peak levels of undesirable electromagnetic emissions. Within each time slot, there may be a period 44 during which all sensors of the plurality of sensors may be measured simultaneously or sequentially. Optionally, an optional pause period may be provided between the last enabled sensor drive and measurement, similar to S112 in FIG. 12. However, such a pause period may generally be unnecessary, since sequentially enabling the drive signals as shown in FIG. 14 may provide unique pause periods for at least sensor 1 and sensor 2 as shown.

[0073] Nevertheless, multiple drive signals may be enabled (and then disabled) simultaneously, e.g., to achieve even faster multiplexing scan rates. In such a parallel drive scheme, the measurement period 44 occurs in the absence of any of the drive signals, so the advantage of reduced EMI can still be achieved.

[0074] FIG. 15a shows an example of a voltage scan of position sensors in a multiplexed keyboard with a continuous measurement process (e.g., as shown in FIG. 8). A continuous drive signal 38 consists of a train of pulses (individual pulses not shown). The multiplexed system drives the detection of a group of eight position sensors, whose detector output signals 43 are shown at the bottom of the graph. Detector signal 43a corresponds to a key in a rest position and signal 43b corresponds to a key that is depressed (e.g., in this example, target 2 and sensor 1 are close to each other). The gaps in the drive signal correspond to a temperature compensation step intervening between the eight multiplexed drive periods. In this step, a direct current is provided that does not affect the output of the position sensors. It should be noted that such a temperature compensation step is optional (e.g., to take into account variations in sensor temperature that may affect the determined sensor output).

[0075] Figure 15b shows a voltage scan for a position sensor similar to Figure 15a, where the drive signal now uses "bursts" 34 of pulses, e.g. as described in relation to Figure 13. Again, eight keys multiplexed are shown, along with a temperature stabilisation step. Detector output 33a shows a key in a rest position, and 33b shows the detector output of a depressed key. Advantageously, the same signal response can be achieved with the drive signal enabled for a much reduced period of time. This can significantly reduce power requirements.

[0076] Figure 16a shows a further example of a voltage scan of a multiplexed keyboard position sensor. Here, an inverted discontinuous drive signal 34 is used to drive the sensor. A temperature compensation step is shown where the detector output signal 45 increases in response to the DC drive signal. Again, the bursts of pulses that form the drive signal 34 are not shown. Additionally, at the bottom of the graph, a timing signal 46 is shown that is used to control each of the multiple cycles. Specifically, nine time slots are shown (eight of which are used to drive each of the groups of eight sensors and one is used to drive the temperature compensation step).

[0077] Figure 16b shows an expanded version of Figure 16a, in which the individual pulses of the pulse train drive signal 34 are illustrated.

[0078] A timing signal 46 is used to indicate the start of each measurement cycle of the nine time slots. Therefore, with regard to synchronization between the drive signal and the measurement timing, it is advantageous to synchronize either the start signal 46 and / or the timing of the drive enable circuit with the underlying frequency of the drive signal 34. This has the advantage of ensuring that the start of the pulse trains are coincident.

[0079] In some instances, simply counting the pulses provides inherent synchronization if the first pulse starts at the same time each time (e.g., not midway through the pulse). In some instances, for example, if a free-running clock is used to control each period of the measurement cycle, the pulse counter may count the same total number of pulses each time. However, the allocation need not be uniform. For example, one cycle may have ¼ pulses at the beginning and ¾ pulses at the end. Another cycle may have ½ pulses at the beginning and end. Each of these pulse trains will drive the resonating sensor differently, resulting in a slightly different output. Therefore, the clock and / or frequency of the drive signal is preferably aligned or matched to the clock and / or frequency of the timer signal 46, so that a repeatable set of pulses is provided each time. Generally speaking, in either scenario, it is advantageous for the start of the first pulse 32 for the drive signal 34 to be the same at each time slot time.

[0080] It will be appreciated that the sensors and corresponding multiplexing systems disclosed herein can be applied to a variety of systems and products, such as piano keyboards (fully electric or integrated into an acoustic piano), computer keyboards (e.g., mechanical keyboards, wired or wireless), computer game controllers, computer touchpads or electronic drawing tablets, electronic drums, pedals, such as guitar pedals, any of the pedals of an electronic piano, and organ pedals. The low power requirements of the embodiments described herein are particularly useful as devices (e.g., wireless devices such as computer keyboards or game controllers) can rely on battery power.

[0081] In general, in related embodiments, the above-mentioned techniques and sensors can be employed to detect pressure in nature, where the sensor includes a deformable element (e.g., a block or layer of rubber) below and / or between one or both of a passive resonant circuit and an active resonant circuit. Such a configuration can be employed, for example, as a sensor for detecting aftertouch on a piano keyboard or computer keyboard. For example, aftertouch (e.g., additional key pressure) applied by a user after a key has already been pressed can be detected by a pressure sensor having a deformable rubber element.

[0082] In the case of an electronic drum with a deformable drumhead or pad mounted on a non-deformable bottom member, either the passive load or active circuitry of the sensor disclosed herein may be mounted or mechanically coupled to the drumhead or pad, and the other of the passive load or active circuitry of the sensor may be mounted on the bottom member. Thus, the relative position and velocity of the drumhead or pad with respect to the bottom member may be sensed. Furthermore, multiple sensors mounted on the drum may allow the spatial location of a strike on the drumhead or pad to be determined, for example, by interpolation or other signal processing.

[0083] Those skilled in the art will no doubt recognize many other valid options, and it is to be understood that the invention is not limited to the described embodiments, but encompasses modifications obvious to those skilled in the art within the scope of the claims appended hereto.

Claims

1. A resonant circuit comprising a passive load and an active circuit, wherein at least one of the active circuit and the passive load is tuned to resonate at a resonant frequency; A driver for driving the active circuit to output an RF signal at the resonant frequency; A drive enable circuit for generating a control signal for enabling and disabling the driver; A sample-and-hold circuit for an amplitude signal indicating the amplitude of an RF signal output from either the passive load or the active circuit, the sample-and-hold circuit holding the peak level of the amplitude signal during the period when the driver is enabled; A measurement circuit for detecting the relative position and / or relative movement of the passive load and the active circuit based on the held peak level, the measurement circuit performing the detection by measuring the held peak level when the driver is disabled by the drive enable circuit; A sensor comprising the above.

2. The sensor according to claim 1, wherein the measurement circuit detects the relative speed of the passive load and the active circuit.

3. The sensor according to claim 1, wherein the sample-and-hold circuit comprises a peak detection input circuit configured to perform amplitude-sensitive demodulation to generate the amplitude signal.

4. The sensor according to claim 3, wherein the peak detection input circuit includes a diode configured to charge a capacitor to generate a voltage corresponding to the peak level.

5. The sensor according to claim 1, wherein the sample-and-hold circuit receives an input signal corresponding to the RF signal from either the passive load or the active circuit, and generates the amplitude signal based on the input signal when the input signal exceeds a threshold voltage.

6. The sensor according to any one of claims 1 to 5, wherein the driver drives the active circuit with a predetermined number of RF pulses during the period when the driver is enabled.

7. The driver has a counter for counting the RF pulses; The sensor according to any one of claims 1 to 5, wherein the drive enable circuit disables the driver when the count reaches a predetermined number.

8. The sample-and-hold circuit is configured to be reset after the measurement and before the next re-enablement of the driver by the drive enable circuit, for the sensor according to any one of claims 1 to 5.

9. The measurement circuit performs the measurement after the elapse of a stop period during which the driver is disabled, for the sensor according to any one of claims 1 to 5.

10. A multiplexer that enables driving a plurality of the resonance circuits simultaneously or at different timings, and during a period in which driving of each of the active circuits by the driver is disabled by the drive enable circuit, the system comprising a multiplexer that enables each measurement circuit to perform the measurement.

11. The system according to claim 10, configured such that the measurements by the respective measurement circuits can be performed simultaneously during the period in which driving of each of the active circuits by the driver is disabled.

12. The passive load comprises a resonance circuit configured to resonate at the resonance frequency when the active circuit is driven by the driver, for the system according to claim 10 or claim 11.

13. The system according to claim 10 or claim 11, wherein the passive load is a conductive target.

14. An apparatus that is a musical instrument keyboard, a computer keyboard, a computer touchpad, a foot pedal, or a drum, the apparatus comprising the system according to claim 10 or claim 11.

15. An apparatus that is a musical instrument keyboard, a computer keyboard, a computer touchpad, a foot pedal, or a drum, the apparatus comprising at least one sensor according to any one of claims 1 to 5.

16. The apparatus is a keyboard for a musical instrument or a computer, the keyboard comprising at least one key or button, the key or button having a movable part comprising either the passive load or the active circuit, and the keyboard having a reference part comprising the other of the passive load or the active circuit, for the apparatus according to claim 15.

17. The sensor according to any one of claims 1 to 5, wherein the passive load includes a resonant circuit configured to resonate at the resonant frequency when the active circuit is driven by the driver.

18. The sensor according to any one of claims 1 to 5, wherein the passive load is a conductive target.

19. The sensor according to claim 17, wherein the active circuit is a resonant circuit configured to resonate at the resonant frequency.

20. The sensor according to claim 17, wherein the active circuit is a resonant circuit configured to resonate at a frequency different from the resonant frequency.

21. The sensor according to claim 17, wherein the sample-and-hold circuit is coupled to the output of the active circuit and is configured to indicate the amplitude of the RF signal output from the active circuit.

22. The sensor according to claim 17, wherein the sample-and-hold circuit is coupled to the output of the passive load and is configured to indicate the amplitude of the RF signal output from the output of the passive load.

23. A method for detecting position or movement, comprising: enabling a driver to drive the active circuit with an RF signal at a frequency that is the resonant frequency of the active circuit or the passive load; sampling, throughout the period during which the driver is enabled, a signal indicating the amplitude of the RF output from the active circuit or the passive load, and holding the peak level of the sampled indication signal; continuing to hold the peak level of the indication signal during at least a portion of a subsequent period during which the driver is disabled; detecting the movement or position of either the active circuit or the passive load relative to the other of the active circuit and the passive load by measuring the held peak level during the portion of the period during which the driver is disabled.

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