Low power wake-up signal detector

Abstract

The present disclosure relates to a method (300) for detection of a wake-up signal in a receiver (10), the method comprising: mixing a received signal with a local oscillator signal to obtain an intermediate frequency, IF, signal; obtaining a delayed IF signal based on the IF signal, by use of a tunable delay element (22); obtaining an exclusive OR, XOR, signal by use of an XOR gate (23) having the IF signal and the delayed IF signal as input signals and having the XOR signal as output signal; obtaining a baseband signal based on the XOR signal; tuning the tunable delay element (22) until at least one level peak of the baseband signal is found; and comparing the baseband signal with a known sequence. The present disclosure further relates to a device, and a receiver performing the method, to an apparatus comprising the receiver, and further to method and receiver for low power receiving of BFSK wake-up signals and apparatus thereof.

Description

[0001] LOW POWER WAKE-UP SIGNAL DETECTOR

[0002] Technical field

[0003] The present invention relates to low-power methods and low-power devices and apparatuses for intermediate frequency (IF) signal detection in a low-power wake-up receiver.

[0004] Background

[0005] Wake-up receivers are used in many loT devices, battery driven wireless devices, devices powered by energy harvesting, and other low-power devices, and also in User Equipment devices, UEs. There are other applications of wake-up receivers in wireless communication such as, for example, smart watches, Virtual Reality (VR) and Augmented Reality (AR) glasses or apparatuses and other power-aware devices and apparatuses. Wake-up receivers have the advantage of being ultra low-power. They typically detect a wake-up signal (WUS) and, when the wake-up signal is detected, they wake up a main unit, which then turns from an idle or powered-off state to a non-idle state or functional state. Therefore, the main device can operate in idle state saving power for a longer time, and further operate in a functional or fully functional state only after being woken up by the wake-up receiver. Once the main device has finished its operation, it can return to the idle state and wait for a control signal from the wake-up receiver to return in its functional or fully functional state. The overall purpose of the wake-up receiver is to save power by having the main unit idle or off for the inactive time. The wake-up receiver itself shall be ultra low-power, for example it should have a sub-mW power consumption.

[0006] Phase and frequency of a received signal are important features in a receiver, and also in a wake-up receiver. The currently existing phase / frequency detectors are predominantly used in frequency synthesizers to achieve an accurate frequency local oscillator signal. However, one of the main drawbacks in choosing the frequency synthesizer to be a Phase Locked Loop ( PLL) or a Frequency Locked Loop (FLL) is the high power consumption. The power consumption of just the PLL can be several milliwatts. Evidently, this is not suitable for ultra low-power receiver applications with sub-mW power consumption targets, such as wake-up receivers. Therefore, PLLs are not suitable for wake-up receivers.

[0007] In low-power receivers, which are using a local oscillator signal and a mixer for downconverting a received signal to an intermediate frequency signal (IF) it is important to have sufficient frequency accuracy in the local oscillator signal for the down converted IF signal to be within a desired frequency band A free-running oscillator may be used, instead of a PLL, in low-power receivers, such as wake-up receivers, since the power consumption of a free- running local oscillator can be quite low. The major drawback with a free-running oscillator, however, is that the frequency of the generated local oscillator is inaccurate and drifts with time.

[0008] Summary

[0009] An object of the present invention is to overcome the problems indicated above.

[0010] According to a first aspect, the present disclosure relates to a method for detection of a wake-up signal in a receiver. The method comprises: mixing a received signal with a local oscillator signal to obtain an intermediate frequency (IF) signal; obtaining a delayed IF signal based on the IF signal, by use of a tunable delay element; obtaining an exclusive OR (XOR) signal by use of an XOR gate having the IF signal and the delayed IF signal as input signals and having the XOR signal as output signal. The method further comprises obtaining a baseband signal based on the XOR signal; tuning the tunable delay element until at least one level peak of the baseband signal is found; and comparing the baseband signal with a known sequence.

[0011] According to a further aspect, the present disclosure relates to a device having as input signal an intermediate frequency (IF) signal. The device comprises: a tunable delay element for obtaining a delayed IF signal; an exclusive OR (XOR) gate having the IF signal and the delayed IF signal as input signals and having a XOR signal as output signal. The device further comprises a first circuit, for obtaining a baseband signal based on the XOR signal; a second circuit for obtaining a comparison of the baseband signal with a known sequence; control logic configured to: tune a delay of the tunable delay element to find at least one level peak of the baseband signal, and a peak detector (PD) for detecting said at least one level peak of the baseband signal.

[0012] According to a further aspect, the present disclosure relates to a receiver comprising the presently disclosed device. In a preferred embodiment, the receiver is a wake-up receiver. In an even more preferred embodiment, the receiver is a wake-up receiver for detection of an On / Off keying wake-up signal. According to a further aspect, the present disclosure relates to an apparatus comprising the presently disclosed receiver. In a preferred embodiment, said apparatus is an internet of things, loT, device, or a smartwatch, or a user equipment (UE), or a or a wireless device, or a battery driven wireless device, or a power-aware wireless device.

[0013] According to a further aspect, the present disclosure relates to a method for detection of a binary frequency shift modulated (BFSK) wake-up signal in a receiver. The method comprises: mixing a received signal with a local oscillator signal to obtain an intermediate frequency (IF) signal; obtaining a first delayed IF signal based on the IF signal, by use of a first tunable delay element; obtaining a second delayed IF signal based on the IF signal, by use of a second tunable delay element; obtaining a first exclusive OR (XOR) signal by use of a first XOR gate having the IF signal and the first delayed IF signal as input signals and having the first XOR signal as output signal. The method further comprises: obtaining a second exclusive OR (XOR) signal by use of a second XOR gate having the IF signal and the second delayed IF signal as input signals and having the second XOR signal as output signal; obtaining a first baseband signal based on the first XOR signal; obtaining a second baseband signal based on the second XOR signal; tuning the first tunable delay element and the second tunable delay element until a level peak of the first baseband signal is found and / or until a level peak of the second baseband signal is found; comparing a third baseband signal with a known sequence.

[0014] According to a further aspect, the present disclosure relates to a receiver for receiving a binary frequency shift modulated (BFSK) wake-up signal, the receiver comprising: a local oscillator; a mixer having as output signal an intermediate frequency (IF) signal, the mixer having as input signals the wake-up signal and an output signal of the local oscillator; a first tunable delay element for obtaining a first delayed IF signal; a first exclusive OR (XOR) gate having the IF signal and the first delayed IF signal as input signals and having a first XOR signal as output signal; a first low-pass circuit, for obtaining a first baseband signal based on the first XOR signal; a second tunable delay element for obtaining a second delayed IF signal. The receiver further comprises: a second exclusive OR (XOR) gate having the IF signal and the second delayed IF signal as input signals and having a second XOR signal as output signal; a second low-pass circuit, for obtaining a second baseband signal based on the second XOR signal; a first peak detector, PD, (75) for finding at least one level peak of at least one of the first and / or second baseband signal. The receiver further comprises control logic configured to: tune a delay of the first tunable delay element and / or tune a delay of the second delay element to find the at least one level peak of at least one of the first and / or second baseband signal; and compare a third baseband signal with a known sequence. The receiver is also such that the third baseband signal is one of the first baseband signal, the second baseband signal, and a combination of the first baseband signal and the second baseband signal.

[0015] According to a further aspect, the present disclosure relates to an apparatus comprising the presently disclosed receiver for BFSK wake-up signal. In a preferred embodiment, said apparatus is an internet of things, loT, device, or a smartwatch, or a user equipment (UE), or a wireless device, or a battery driven wireless device, or a power-aware wireless device.

[0016] In the present disclosure, whenever using the term known sequence or pre-determined sequence, it is intended a digital sequence that is known to both transmitter and receiver, for example because it has been hand-shaken before transmission and / or reception. Digital sequence may be a sequence of “logical Is” and / or “logical Os”

[0017] Further embodiments are defined in the dependent claims and in the detail description. It should be emphasized that the term “comprises / comprising” when used in this specification is taken to specify the presence of stated features, integers, steps, or components, but does not preclude the presence or addition of one or more other features, integers, steps, components, or groups thereof.

[0018] Brief description of the drawings

[0019] Fig. 1 illustrates Phase Locked Loop (PLL) power consumption as a function of output frequency.

[0020] Fig. 2 illustrates a block diagram of a low-power wake-up receiver according to an embodiment of the present disclosure.

[0021] Fig. 3 illustrates a block diagram of a device having as input signal an intermediate frequency, IF, signal according to some embodiments of the present disclosure.

[0022] Fig. 4 illustrates a configuration of input intermediate frequency, IF, signal, a delayed IF signal when the delay is equal to zero, and a XOR signal output.

[0023] Fig. 5 illustrates a configuration of input intermediate frequency, IF, signal, a delayed IF signal when the delay is equal to half a period, and a XOR signal output.

[0024] Fig. 6 illustrates a level of a baseband signal as a function of a delay of a tunable delay element: peaks are observed at odd half period-multiples delays.

[0025] Fig. 7 illustrates a flow chart of a method for detecting an IF signal according to some embodiments of the present disclosure.

[0026] Fig. 8 illustrates a flow chart of a method for detecting a wake-up signal according to some embodiments of the present disclosure.

[0027] Fig.9 illustrates a power of a low pass filtered XOR signal as a function of a power of an input IF signal.

[0028] Fig. 10 illustrates an IF detector in case of a Binary Frequency Shift Keying (BFSK) modulation of the wake-up signal, according to an embodiment of the present disclosure.

[0029] Fig.l 1 illustrates an IF detector in case of a Binary Frequency Shift Keying (BFSK) modulation of the wake-up signal, according to another embodiment of the present disclosure.

[0030] Detailed description

[0031] In the present section, whenever using the word “the method” or “said method” or “presently disclosed method”, the reference is to the Method for detection of a wake-up signal according to the first aspect of the present disclosure.

[0032] A wake-up receiver typically comprises a local oscillator generating a local oscillator signal and a mixer, which mixes a wake-up signal with the local oscillator signal. The wakeup signal, which is a wireless signal, is typically captured by an antenna or an array of antennas, which may typically be shared with a main unit in the same device. The mixing of the wake-up signal with the local oscillator signal results in an intermediate frequency (IF) signal. However, the frequency of the generated local oscillator, if for example the local oscillator is a free running oscillator, is inaccurate and drifts with time, which is a problem, for example because the IF signal may drift away from a pass-band of a filter. In less power constrained receiver said problem may be solved by use of a Phase Locked Loop (PLL). If a PLL is used as local oscillator, that may guarantee a nearly constant frequency of the local oscillator signal.

[0033] Fig. 1 illustrates Phase Locked Loop (PLL) power consumption as a function of output frequency. Power of a PLL is in the mW range and increases dramatically with frequency, reaching tens and hundreds of mW. Therefore a PLL, which might be an obvious design choice in a less power constrained receiver, is to be avoided in a low-power receiver such as a wake-up receiver.

[0034] The purpose of a wake-up receiver is to function at sub-mW power consumption levels, and capture a wake-up sequence sent over the air by a transmitter. Only when the correct wake-up sequence is detected by the wake-up receiver, then the wake-up receiver sends a wake-up signal to a main unit and enables the main unit to get ready (for example power up, or exit from idle state to enter functional state) to receive and / or send the actual data-stream using a separate main receiver and or main transmitter. The main unit and the wake-up receiver may be within the same device, such as a User Equipment (UE), mobile phone, cellular phone, loT device, smart watch, Virtual Reality (VR) glasses, Augmented Reality (AR) glasses and other devices where power consumption is a concern.

[0035] By using a wake-up receiver the main unit can be powered-off or idle for all inactive time, that is, for example, when there is no data content to receive or transmit, and can operate fully only when actually needed, that is, for example, when a transceiver from a unit, for example a base station, or another UE, or any other wireless device, signals by sending a wake-up sequence that the third transceiver is actually prepared to send some data content (data and / or control) to the main unit or to receive some information (data and / or control) from it.

[0036] The present disclosure solves, among others, the problem of the frequency drift of the intermediate frequency, IF, signal, without using a power hungry PLL for the local oscillator, and thus maintaining low power consumption, preferably sub-mW power consumption.

[0037] Fig 2 is a block diagram of a wake-up receiver 10 according to some embodiments of the present disclosure. At least one antenna 11 captures a wireless signal at radiofrequency (RF) and sends it to an RF front-end with mixers, 12. Said front-end 12 comprises a local oscillator (not shown) and a mixer (not shown). One input of the mixer is connected to the RF signal. A second input of the mixer is connected to a local oscillator output. The RF signal is down- converted to an intermediate frequency (IF) and optionally amplified with an IF amplifier, 13. IF detection block 20, also referred to as device 20, receives the IF signal as input. Block 20 determines if the captured IF signal is the correct one, that is if it contains a correct sequence, by comparing the received sequence with a known sequence. In a scenario, a transmitter sends an RF signal modulated based on a known sequence. In one embodiment the transmitter may send a On / Off keying modulating signal. In another embodiment the transmitter may send a Binary Frequency Shift Keying (BPSK) signal. In some embodiments of the present invention, a captured sequence is the correct one if that sequence has a correlation to a known sequence more than or equal to a first threshold. If the detected sequence is not the correct one, a control block 14, based on an input from block 20, may adjust a frequency of the local oscillator so that the receiver tunes to a different RF signal corresponding to a different IF signal. In addition, in a wake-up receiver having a narrowband IF band-pass filter, the control block may adjust the frequency of the local oscillator also based on the delay of the tunable delay element. In this embodiment, if a correct sequence is detected in correspondence to a value of the delay element that has a difference to a desired delay value higher than a third threshold, then the VCO frequency may be adjusted to have the IF signal at the center of the narrowband band-pass filter. In this embodiment, the desired value of the tunable delay element may correspond to a center frequency of the narrowband IF filter.

[0038] Fig. 3 is a block diagram of a device 20, also referred to as IF detection block 20, according to an embodiment of the present disclosure. Device 20 has, as input signal, an IF signal coming from a mixer or an IF amplifier and / or optionally an IF filter, wherein the IF filter may be a narrowband IF filter. In this embodiment the RF signal, and therefore the IF signal may be modulated with an On / Off keying modulation. Device 20 comprises a tunable delay element 22 for obtaining a delayed IF signal. The tunable delay element may, for example delay the IF signal by a fraction of the period of the IF signal. Device 20 may further comprise an exclusive OR (XOR) gate 23 having the IF signal and the delayed IF signal as input signals and having an XOR signal as output signal.

[0039] As shown in Fig. 4, in correspondence to a zero delay, the XOR signal may be substantially zero both in case of a logic 1 and a logic 0. As shown in Fig. 5, in correspondence to a delay of the tunable delay element equal to half a period of the IF signal the XOR signal may be maximum in correspondence to all duration of a logic 1.

[0040] With reference to Fig. 3, the XOR signal is low-pass filtered by use of a low-pass filter 28 to obtain a baseband signal. Depending on the delay of the delay element, a power or level or voltage or amplitude of the baseband signal may vary.

[0041] As shown in Fig. 6, the level of the baseband signal depends on the tunable delay element and varies according to the graph shown in Fig. 6. Maximum is found at half a period of the IF signal or at odd multiples of half a period.

[0042] With reference to Fig. 3, a peak detector 25 is used to detect the level of the baseband signal. If the level of the baseband signal is below a first threshold, then the control logic 27 is configured to tune the delay of the tunable delay element until a peak is found. A peak is found if the level of the baseband signal is above a first threshold. Once a peak is found, device 20 is configured for checking whether the IF signal carries a correct sequence. That is done by use of comparison circuit 26 which compares the sequence carried by the baseband signal with a known sequence. In some embodiments the comparison may be a correlation. If the comparison reveals that the sequence is not the correct one, for example because the baseband sequence has a correlation, with the known sequence, below a second threshold, device 20 is configured to change a frequency of the local oscillator or to look for another peak by changing a delay of the tunable delay element. Device 20 may change the frequency of the local oscillator by use of control signal 29. When the frequency of the local oscillator is changed another RF signal is detected and therefore another IF signal, that may be carrying a correct sequence. If the sequence of the baseband signal is correct, device 20 is configured to retain the frequency of the local oscillator or to fine tune the IF frequency in such a way that a delay of the tunable delay element, when tuned to the signal peak with correct sequence, corresponds to a desired value, or in such a way that a difference between the delay of the tunable delay element and the desired value is less than a third threshold. In this embodiment, the desired value of the tunable delay element corresponds to a center frequency of a narrowband IF band pass filter. Method for detection of a wake-up signal

[0043] According to a first aspect, the present disclosure relates to a method 300 for detection of a wake-up signal in a receiver 10, the method comprising: mixing a received signal with a local oscillator signal to obtain an intermediate frequency, IF, signal; obtaining a delayed IF signal based on the IF signal, by use of a tunable delay element 22; obtaining an exclusive OR (XOR) signal by use of an XOR gate 23 having the IF signal and the delayed IF signal as input signals and having the XOR signal as output signal. The method further comprises: obtaining a baseband signal based on the XOR signal; tuning the tunable delay element 22 until at least one level peak of the baseband signal is found; and comparing the baseband signal with a known sequence.

[0044] The presently disclosed method has the advantage to provide a low power detection of the wake-up signal and / or of any wake-up sequence or synchronization sequence. In particular it provides a low-power detection of a digital sequence carried by a wake-up signal. The sequence may be a wake-up sequence or a synchronization sequence. It may be a predetermined or known sequence. The detection is low power because, among others, the local oscillator is controlled without using a PLL.

[0045] In the present disclosure, the use of expressions as “digital sequence” or “logical sequence” or “sequence” are equivalent and indicate a sequence of binary digital values, as for example “logic 1” or “logic 0”, or “1” or “0”, or “high” or “low”.

[0046] By level peak of a baseband signal, in the present disclosure, it is meant a peak in a power and / or in a voltage amplitude of the baseband signal.

[0047] Fig. 7 is a flowchart of the method 300 according to some embodiments of the present disclosure. The method 300 may comprise: mixing a received signal with a local oscillator signal to obtain an IF signal, 301; obtaining a delayed IF signal, based on the IF signal, by use of a tunable delay element, 302; obtaining an XOR signal of the IF signal and the delayed IF signal, 303; obtaining a baseband signal based on the XOR signal, 304; tuning a delay of the tunable delay element to find at least one level peak of the baseband signal, 305; comparing the baseband signal, with a pre-determined or known sequence; 306. In one embodiment, the wake-up signal may be modulated with an On / Off keying modulation. An On / Off modulated wake-up signal may comprise a digitized sequence. For example, whenever a “digital 0” is modulated, an On / Off keying signal may be substantially zero. Whenever a “digital 1” is modulated, an On / Off keying signal may be oscillating at an RF frequency, or at an IF frequency depending at what stage the signal is, at a maximum amplitude.

[0048] Some examples of how the different steps in Fig. 7 may be performed are described below.

[0049] In step 301 a received signal, wake-up signal or RF signal, may be mixed with a local oscillator signal to obtain an IF signal. This is done in order to down convert the wake-up signal, or RF signal, to an intermediate frequency which is more energy efficient for further signal processing. By use of a mixer and a local oscillator an IF signal is obtained which is carrying substantially a same On / Off sequence as the wake-up signal. The IF signal may be at a lower frequency than the wake-up signal. The frequency of the IF signal may be determined by a difference between a frequency of the wake-up signal and a frequency of the local oscillator signal. The mixer, which is mixing the wake-up signal, or the RF signal, with the local oscillator signal, is acting as a down-converter.

[0050] However, in a receiver with a free running local oscillator without any frequency control, if a frequency of the local oscillator signal drifts too much, then the wake-up signal cannot be detected. For example, the IF signal may end up outside of a frequency window of a filter in the receiver chain. The problem is solved without using a PLL by using the method claimed in the present disclosure.

[0051] In step 302, the IF signal may be delayed by a tunable delay element 23, to obtain a delayed IF signal.

[0052] A tunable delay element may be comprising active and / or passive circuit elements. An example of said tunable delay element may be provided by B. Schell and Y. Tsividis, "A Low Power Tunable Delay Element Suitable for Asynchronous Delays of Burst Information," in IEEE Journal of Solid-State Circuits, vol. 43, no. 5, pp. 1227-1234, May 2008, doi: 10.1109 / JSSC.2008.920332. Such a tunable delay element is low power and is suitable for low-power wake-up receivers.

[0053] The tunable delay element may be tunable, in one embodiment, by control logic in the wake-up receiver. In particular the tunable delay element 22 may be tunable to a portion of the period of the IF signal, said portion being a fraction of the period. The tunable delay element may also be tunable to a multiple of a fraction of the period of the IF signal. The tunable delay may be tuned by use of a delay-control signal from the control logic to the tunable delay.

[0054] In step 303, an XOR signal may be obtained based on the IF signal and the delayed IF. The IF signal and the delayed IF signal may be XORed by using a logical XOR function block, such as an XOR gate 23. In the present disclosure, by XOR gate it is meant any XOR or XNOR gate or any digital or analog gate, circuit or device that can perform a logic XOR or a logic XNOR or any other exclusive OR functions of digital or analog signals. The IF signal and the delayed IF signal may be fed to inputs of an XOR gate, and an XOR signal may be generated. As illustrated in Fig. 5, If the delay of the delayed IF signal is equal to half a period of the IF signal, or an odd multiple of half a period, then the XOR signal may be a logic “1”, or high value, for substantially all the duration of an IF signal high logic period. With logic period it is intended a period of time where the IF signal is, for example “On” or “Off’ corresponding to a “logic 1” or a “logic 0”, according to, for example, an On / Off modulation scheme (On / Off Keying), where “On” and “Off’ are denotating respectively “logic 1” and “logic 0”, or “1” and “0” or “high” and “low” or any binary digitized value.

[0055] If the delay is zero instead, the XOR signal may be substantially zero during both the On and Off time of the IF signal, as illustrated in Fig. 4. In intermediate cases, wherein the delay of the tunable delay element is between zero and half a period of the IF signal, the XOR signal, during the On logic period, may be alternatively high and low, with an average value that is increasing by increasing the delay.

[0056] In step 304 of method 300, a baseband signal may be obtained based on the XOR signal. In particular the XOR signal may be low-pass filtered or envelope detected to obtain the baseband signal. The baseband signal is substantially a low-pass version of the XOR signal. The XOR signal may be low passed filtered by means of a low-pass filter or by means of an envelope detector or by means of any IF / baseband converter. Other low-pass filtering implementations may be used.

[0057] A baseband signal may be obtained based on the XOR signal. The baseband signal may be a low-pass filtered version of the XOR signal. The XOR signal may contain non-desired high- frequency components, that may be filtered out by the low-pass filtering. The low pass filtering may be an envelope detection. If the IF signal is modulated with On / Off keying, the baseband signal carries a baseband version of the On / Off sequence of the wake-up signal. The signal-to-noise-floor ratio of the baseband signal is maximum when the power of the baseband signal is maximum, that is in correspondence of the half period delay of the delay element or in correspondence to odd multiples of the half period, wherein the half period is a half period of the IF signal.

[0058] This filtering is advantageous because it converts the IF signal to baseband and a simple peak detector can be used to detect the level of the baseband signal. By level of the baseband signal it is intended an amplitude of the voltage or power of the baseband signal. The baseband signal is reproducing, at baseband frequencies, substantially the same sequence as the wake-up signal. When the tunable delay is at different values than half a period or odd multiples of half a period of the IF signal, then the level of the baseband signal is less than its maximum, as illustrated in Fig. 6. By level peak of a baseband signal, in the present disclosure, it is meant a peak in a power and / or in a voltage amplitude of the baseband signal.

[0059] In step 305, the method 300 comprises tuning a delay of the tunable delay element to find a peak of the baseband signal.

[0060] Fig. 6 illustrates how the level of the baseband signal, which is substantially a low-pass filtered version of the XOR signal, may be a function of the delay of the tunable delay element. From Fig. 6 it is clear that the level peaks may be found around half period of the IF signal (corresponding to 1 ns for a 0.5 GHz IF signal) or at odd multiples of the half period (for example, at 3 ns and at 5 ns). In correspondence to these level peaks, the power of the baseband signal may be highest with respect to the noise floor and therefore the signal-to- noise-floor ratio may be maximized, minimizing the error-rate in detecting the received sequence by a baseband circuit receiving the baseband signal.

[0061] Therefore a tuning of the delay element may be done until at least one level peak is found. During tuning of the tunable delay, a level of the baseband signal may be measured using, for example, a peak detector. In one embodiment, once a level peak is found, the tunable delay may be kept at the value that corresponds to the level peak. The control logic may control the tunable delay element such as to sweep the delay of the tunable delay element in order to find and record a plurality of level peaks of the baseband signal. A level peak of the baseband signal is found when a level of the baseband signal is more than or equal to a first threshold.

[0062] In step 306, when a level peak is found, the method comprises comparing the baseband signal with a known or pre-defined sequence. The comparison may be a correlation and may be performed by second circuit 26, which may, in one embodiment, be a correlator. If the tunable delay is swept and a plurality of level peaks of the baseband signal are found, the comparison or correlation may be performed in correspondence to some or all the found level peaks.

[0063] In some embodiments the method may comprise comparing a low-pass filtered IF signal or an envelope detected version of the IF signal with the known sequence. In this embodiment, an envelope detector or a low pass filter may be used to obtain a low-pass filtered IF signal based on the IF signal. In this embodiment, the low-pass filtered IF signal may be compared to the known sequence.

[0064] In an other embodiment, the baseband signal, that is the low-pass filtered XOR signal, may be compared to the known sequence.

[0065] Further embodiments of Method for detection of a wake-up signal

[0066] In one embodiment, the above disclosed method further comprises outputting a control signal for tuning a frequency of the local oscillator signal, based on the comparison of the baseband signal with the known sequence and / or based on a value of the tunable delay element. This is advantageous to be able to control the frequency of the local oscillator in order to tune the wake-up receiver to a correct IF signal and therefore a correct wake-up signal.

[0067] With reference to Fig. 3 the frequency of the local oscillator may be tuned by use of a control signal 29. The local oscillator may advantageously be a voltage controlled oscillator (VCO), wherein a control signal is used to tune the frequency of the VCO. Said control signal is defining frequency settings of the VCO.

[0068] In some scenarios, an apparatus implementing the method above method may be located in an area where a plurality of transmitters of wake-up signals are located, such that all or some of these transmitters transmit wake-up signals within the wireless reach of said apparatus, some of said wake-up signals not being intended (or not being correct) for said apparatus. One transmitter may instead transmit a wake-up signal which is intended (correct) for said apparatus.

[0069] This means that the apparatus comprising a wake-up receiver may measure one or more level peaks in correspondence of wake-up signals corresponding to one or more transmitters that are not intended, or are not correct. For example a non-intended transmitter at frequency fl may send a strong signal at frequency fl and the receiver may find a level peak in correspondence to a local oscillator frequency LO1 and a delay of the tunable delay element DI. If the wake-up signal is intended or not for said apparatus may be determined based on a sequence, such as a wake-up sequence or other known sequence. Each transmitter-receiver pair may have a separate pre-determined (or known or hand-shaken) sequence and that sequence is known to the transmitter and the receiver and is pre-determined. If the signal is not intended, the received sequence may not correlate with the known sequence.

[0070] Fig. 8 is a flowchart of some embodiments of a method 130.

[0071] In step 131, the method 130 may start from a default local oscillator frequency, which may be a central frequency of the local oscillator or a central frequency of the VCO. That is the VCO is set, to start with, to produce a local oscillator signal corresponding to a center frequency of the VCO.

[0072] In step 132 the method 130 may further comprise sweeping a delay of the tunable delay element to find at least one level peak.

[0073] In step 133 the method 130 may further comprise sorting the found level peaks based on strength. This is advantageous as, in a more likely scenarios, the intended wake-up signal may have more strength than non-intended signals. However, there is no guarantee for that, but it is still statistically advantageous, for statistically faster convergence of the method, to start from the level peak of higher strength. In step 134 the method 130 may comprise, for at least one or at least some or for each level peak found, checking with the correlator if the detected signal is the correct signal. A sequence detection and comparison or correlation may be done to ensure that the sequence is the correct known or pre-determined sequence with a probability above a certain threshold. This may be done by a comparison or a correlation between a received sequence and a predetermined or known sequence. In correspondence to at least one or at least some or each level peak a comparison of a sequence of the baseband signal with a pre-determined or known sequence is performed, for example by use of a correlator circuit. If a comparison or a correlation of the baseband signal with the known sequence is less than a second threshold, then the detected signal is non-intended. If a comparison or a correlation of the baseband signal with the known sequence is more than or equal a second threshold, then the detected signal is intended. Some of the found level peaks may be corresponding to non-intended wake-up signals. Some of the found level peaks may correspond to intended wake-up signals.

[0074] In step 135 of method 130, if the result of the comparison or the correlation is more than or equal to a second threshold, in correspondence to at least one level peak of the baseband signal, then the receiver is tuned to a correct wake-up signal and the VCO setting may be retained, that is the VCO may retain its output frequency, which is a frequency of the local oscillator. In this case the method may end here or the VCO is tuned so that a desired IF frequency is obtained for the correct wakeup signal, i.e. the level peak occurs for a predetermined or desired delay of the tunable delay element. In this embodiment, if the sequence is the correct one in correspondence to a delay of the tunable delay element whose difference from a desired delay is greater than a third threshold, then the VCO may be fine tuned to correspond substantially to the desired delay. In this embodiment, the desired delay corresponds substantially to a frequency of the IF signal corresponding substantially to a central frequency of narrowband band-pass IF filter.

[0075] In step 136 of method 130, if the result of the comparison or the correlation is below a second threshold in correspondence to all found level peaks, that may indicate that the receiver is tuned to a frequency range containing only non-intended wake-up signals or other non-intended signal such as intermodulation interference from a clipper, such as clipper 21 in Fig. 3. By non-intended signal it is meant a signal that does not carry the known or predetermined sequence.

[0076] Therefore the frequency of the local oscillator may be tuned to a different frequency and therefore a control logic of the wake-up receiver may control the VCO so as to change a frequency of the local oscillator signal.

[0077] After step 136, the method 130 may iteratively be executed by starting again from stepl32, in correspondence to a different frequency of the local oscillator signal, or different setting of the VCO.

[0078] By tuning the local oscillator frequency in steps and, after finding a level peak and comparing or correlating the received sequence with the pre-determined or known sequence the method may eventually converge and find the correct local oscillator frequency and then stay tuned to the correct frequency setting of the local oscillator.

[0079] Further embodiments of the Method for detection of a wake-up signal

[0080] In one embodiment, the wake-up signal may be an On / Off keying signal.

[0081] In one embodiment, a level peak of the baseband signal is found if a level of the baseband signal is more than or equal to a first threshold. A first threshold may be set, for example by analyzing a level curve such as the level curve shown in Fig. 6.

[0082] In one embodiment the method further comprises tuning a delay of the delay element if a level of the baseband signal is below a first threshold. A delay of the tunable delay element may be swept. For example the delay may initially be set to zero, then increased progressively. When a level of the baseband signal exceeds or is equal to a first threshold, the delay may be kept to the value corresponding to the peak, and a sequence correlation may be performed. Other algorithms for the level peak search may be used.

[0083] In one embodiment, a delay of the tunable delay element may be swept. For example the delay may initially be set to zero, then increased progressively. When a level of the baseband signal exceeds or is equal to a first threshold, the corresponding delay may be recorded by a control unit. Then the delay may be increased further and a second level peak may be found. That may be recorded. In correspondence to at least one or some or all of the found level peaks, a sequence comparison or correlation between the baseband signal and the known sequence may be performed. If no level peak is found, the VCO frequency is changed and level peaks may be searched by sweeping the tunable delay element in correspondence to a changed VCO frequency.

[0084] In one embodiment the wake-up signal is detected when the baseband signal at least partly matches the known sequence. In correspondence to a level peak of the baseband signal a comparison or a correlation of the baseband signal, which carries a sequence, with a known sequence is performed. If the comparison matches at least partly, then the wake-up signal is detected and the settings of the VCO are kept, that is the frequency of the local oscillator is kept. If the comparison matches at least partly in correspondence to a value of the delay element that has a difference to a desired delay value higher than a third threshold, then the VCO frequency may be adjusted to have the IF signal at the center of a narrow-band pass filter. In this embodiment, the desired value of the tunable delay element may correspond to a center frequency of the narrowband IF filter. In this way a fixed IF narrow-band filter may be used, with advantages in power consumption, cost and sensitivity of the received signal.

[0085] In one embodiment comparing the baseband signal with a known sequence comprises correlating the baseband signal with the known sequence. In this embodiment, the comparison is preferably done by use of a correlator circuit. In this embodiment, a second threshold is established based, for example, on statistical data. If the correlation is more than or equal to the second threshold, then the correct sequence is detected.

[0086] In one embodiment the method further comprises tuning a frequency of the local oscillator signal if the correlation of the baseband signal with the known sequence is below a second threshold, or if a difference between a delay of the delay element and a desired delay value is greater than third threshold. If the correlation is more than or equal than the second threshold, the settings of the VCO are retained, that is the frequency of the local oscillator is retained, and the wake-up signal is detected. If the correlation is more than or equal to the second threshold in correspondence to a value of the delay element that has a difference to a desired delay value higher than a third threshold, then the VCO frequency may be adjusted to have the IF signal at the center of a narrow-band pass filter. In this embodiment, the desired value of the tunable delay element may correspond to a center frequency of the narrowband IF filter. If the correlation is below the second threshold, then the frequency of the VCO is changed, that is the frequency of the local oscillator is changed. Additionally, after finding the correct signal the method may further comprise tuning the VCO to obtain a predetermined IF frequency, corresponding to a desired delay of the tunable delay element. This has the advantage that more narrow IF filter may be used to reduce interference and noise.

[0087] In one embodiment the IF signal is clipped between rails of a digital supply voltage before being fed to the tunable delay element and / or to the XOR gate. This has the advantage of generating a square waveform of the IF signal at a frequency of the IF signal. This has the advantage to provide pseudo-digitized signal before the XOR operation, obtaining better operation of the XOR gate, which is typically better performing when being inputted with digitized signals. In addition, the use of clipped signal also has the advantage that the tunable delay circuit is simpler, easier to implement and less power-hungry. A clipper circuit may be used for that purpose. The non linearities of the clipper may induce odd-order intermodulation distortion. This may result in additional non-intended level peaks. However these level peaks related to intermodulation distortion may typically have a lower strength than the level peaks corresponding to intended wake-up signals. The negative effect of these peaks may be mitigated by performing the correlation in correspondence to level peaks in descending strength order. However, if the intermodulation should affect the baseband signal, that would result in lower signal-to-noise ratio. A lower signal-to-noise ratio may be defeated by increasing the correlation time of the sequence correlation.

[0088] In one embodiment the method further comprises adjusting a correlation time of the correlation based on an indication of a signal-to-noise ratio of the baseband signal.

[0089] In one embodiment the method further comprises sweeping a delay of the tunable delay element to obtain the at least one level peak of the baseband signal. By sweeping the delay of the tunable delay elements, several level peaks may be found, some of them corresponding to non-intended signals. In one embodiment the level peaks are then sorted in descending strength order and a sequence correlation is performed between the corresponding baseband signals and the known sequence. In one embodiment, if all the obtained correlation values are below the second threshold, then a frequency of the local oscillator signal may be tuned (changed), otherwise the frequency of the local oscillator signal may not be tuned and the VCO settings may be retained or, if the correlation is more than or equal to the second threshold in correspondence to a value of the delay element that has a difference to a desired delay value higher than a third threshold, then the VCO frequency may be adjusted to have the IF signal at the center of a narrow-band pass filter. In this embodiment, the desired value of the tunable delay element may correspond to a center frequency of the narrowband IF filter.

[0090] In one embodiment, tuning the frequency of the local oscillator signal may be done in steps.

[0091] In one embodiment, tuning the frequency of the local oscillator signal may comprise starting from selecting a center frequency of the variable oscillator and then following an alternating pattern on a higher and a lower side of the center frequency, said alternating pattern progressively moving from the center frequency to frequencies progressively further away from the center frequency.

[0092] Device

[0093] According to a further aspect, the present disclosure relates to a device 20 having as input signal an intermediate frequency (IF) signal, the device comprising: a tunable delay element 22 for obtaining a delayed IF signal; an exclusive OR (XOR) gate 23 having the IF signal and the delayed IF signal as input signals and having a XOR signal as output signal; a first circuit 28, for obtaining a baseband signal based on the XOR signal; a second circuit 26 for obtaining a comparison of the baseband signal with a known sequence; control logic configured to: tune a delay of the tunable delay element 22 to find at least one level peak of the baseband signal, and a peak detector, PD, 25 for detecting said at least one level peak of the baseband signal.

[0094] The presently disclosed device 20 is configured to be used in a wireless wake-up receiver 10 as shown in Fig. 2. An example of a wake-up receiver is provided in Fig. 2, showing a block-diagram of an example of a wake-up receiver. A wake-up receiver 10 may comprise at least one antenna 11, a Radio Frequency Front-End 12 comprising a matching network, a local oscillator or VCO and a mixer, an optional IF amplifier 13, a device as presently disclosed with IF signal as input 20, and a control block 14. Still with reference to Fig. 2, a wake-up signal, or RF signal, is captured by at least one antenna 11, it is then mixed by a mixer (not shown) with a local oscillator signal from a local oscillator (not shown), which may be a VCO. An IF signal is therefore generated, which is an input to the presently disclosed device 20. The presently disclosed device is indicated in Fig. 2 and Fig. 3 with reference 20.

[0095] Fig. 3 is an example of a device (20), having an IF signal as input signal, according to some embodiments of the present disclosure.

[0096] In some embodiments, the device 20, when used in a wake-up receiver, such as the wakeup receiver 10 in Fig.2, has the advantage to be able to provide an indication of the correctness of a frequency of a local oscillator. In one embodiment, when the device 20 is used in a wake-up receiver, it further has the advantage to provide a control signal 29 for tuning a frequency of the local oscillator and to identify a correct local oscillator frequency for correct reception.

[0097] Still with reference to Fig. 3 the presently disclosed device 20 may comprise: a tunable delay element 22 for obtaining a delayed IF signal; an exclusive OR (XOR) gate 23 having the IF signal and the delayed IF signal as input signals and having a XOR signal as output signal. The device may further comprise a first circuit 28, for obtaining a baseband signal based on the XOR signal; a second circuit 26 for obtaining a comparison of the baseband signal with a known sequence; and control logic.

[0098] The tunable delay element 22 may be used to obtain a delayed IF signal based on the IF signal.

[0099] The XOR gate 23 may be used to obtain a XOR signal based on the IF signal and the delayed IF signal. Examples of XOR signals are provided in Fig. 4 and Fig 5.

[0100] The first circuit 28 may be used to obtain a baseband signal based on the XOR signal. Examples of first circuits are a low-pass filter or an envelope detector.

[0101] In one embodiment, the wake-up signal is an On / Off keying modulated signal and the baseband signal carries a sequence that is carried by the wake-up signal and the IF signal. However the baseband signal has a higher signal-to-noise-floor ratio in correspondence to a level peak of the baseband signal because in correspondence to the level peaks, the baseband signal level increases compared to the noise floor.

[0102] A level peak of the baseband signal is found in correspondence to a delay of the tunable delay element which corresponds to half a period of the IF signal or to odd half periodmultiples delays as shown in Fig. 6.

[0103] The device 20 may comprise a peak detector 25 for obtaining a level, such as amplitude or power or voltage, of the baseband signal. The peak detector 25 may be connected to a control logic 24, 27, which may be storing the level values and may control a delay of the tunable delay element 22, for example based on the level of the baseband signal, or for example by sweeping a delay of the tunable delay element. The control logic may be storing the level values or the control logic may store the level peaks values. A level peak is found if the level is more than or equal to a first threshold. As the level of the baseband signal depends on the delay of the tunable delay element, the control logic may sweep the values of the delay of the tunable delay element in order to find level peaks of the baseband signal. In correspondence to those peaks, and optionally after sorting them based on strength in descending order, the control logic 24, 27, may use the second circuit 26 to compare the baseband signal, which carries a logic sequence, with a known or pre-defined sequence. Based on the comparison or correlation, the control logic may drive the control signal 29 to: if the result of the comparison or the correlation is more than or equal to a second threshold in correspondence to at least one of the level peaks, control the VCO to retain its output frequency or fine-tune it to match a desired delay of the tunable delay element. Based on the comparison or correlation, the control logic may drive the control signal 29 to: if the result of the comparison or the correlation is below a second threshold in correspondence to all found level peaks for a specific first VCO frequency, tune the VCO to a different frequency than the first VCO frequency.

[0104] The process of finding level peaks of the baseband signal by changing a delay of the tunable delay element, obtaining a correlation in correspondence of the level peaks and, based on the correlation, retaining or changing the frequency of the local oscillator, may be repeated until a correlation above or equal to a second threshold is achieved.

[0105] In some embodiments, the comparison may be a correlation and the second circuit may be a correlator.

[0106] In some embodiments, the duration of the correlation may be adjusted based on a detected signal-to-noise ratio. In one embodiment, the device 20 further comprises a signal clipper 21 to clip the IF signal before the IF signal is fed to an input of the XOR gate and / or to an input of the tunable delay element 22. That is advantageous to digitize the IF signal and the delayed IF signal in order to more efficiently use a digital XOR gate and to simplify the delay circuit.

[0107] In one embodiment, the second circuit for obtaining the comparison is a correlator and the comparison is a correlation. This feature is advantageous as the correlation time of a correlator may be increased to achieve better correlation of baseband signals when they have a worse signal-to-noise ratio. This is advantageous if, for example, the signal to noise ratio of the baseband signal is made worse by spurious signals from the clipper.

[0108] In one embodiment, the first circuit 28 is a low-pass filter or an envelope detector. The first circuit 28 may be any low-pass circuit used to obtain a baseband signal from an XOR signal.

[0109] In one embodiment, the tunable delay element 22 comprises passive and / or active components. In a further embodiment, the tunable delay element, TDE, may be implemented according to the reference from B. Schell as above: B. Schell and Y. Tsividis, "A Low Power Tunable Delay Element Suitable for Asynchronous Delays of Burst Information," in IEEE Journal of Solid-State Circuits, vol. 43, no. 5, pp. 1227-1234, May 2008, doi: 10.1109 / JSSC.2008.920332.

[0110] In one embodiment, the control logic is further configured to, based on the comparison of the baseband signal with a known sequence, output a control signal 29. Said control signal is used to control the frequency of the local oscillator signal, for example by controlling the vco.

[0111] In one embodiment, a frequency of a local oscillator signal, is tuned or changed based on the control signal 29 if the correlation is below a second threshold. In one embodiment, if the correlation is more than or equal to a second threshold, the frequency of the local oscillator is retained. The control logic may be configured to control the control signal 29.

[0112] In one embodiment, the presently disclosed device 20 is further configured to carry out the presently disclosed method 300. In one embodiment, the presently disclosed device 20 is further configured to carry out the presently disclosed method 130.

[0113] It is clear to the person skilled in the art that the control logic 24, 27 of the presently disclosed device 20 is configured to drive the device 20 to carry out the steps of the presently disclosed method 300 in all or some of the embodiments of the method 300.

[0114] It is clear to the person skilled in the art that the control logic 24, 27 of the presently disclosed device 20 is configured to drive the device 20, when the device 20 is part of a wakeup receiver 10 to carry out the steps of the presently disclosed method 300 in all or some of the embodiments of the method 300.

[0115] In the example of Fig.3, the control logic of the device is depicted in Fig. 3 as block Control_2, 27, or the control logic may be a combination of control block 27 and control block 24 or any combination thereof. The control logic may optionally at least partly comprise Control Block 1 14 of Fig. 2.

[0116] Receiver

[0117] According to a further aspect, the present disclosure relates to a receiver 10 comprising the presently disclosed device 20. In a preferred embodiment, the receiver 10 is a wake-up receiver. In an even more preferred embodiment, the receiver is a wake-up receiver for detection of an On / Off keying signal, or an On / Off keying wake-up signal.

[0118] In the present section, whenever using the word “the receiver” or “said receiver” or “presently disclosed receiver”, the reference is to the receiver comprising the device 20 according to a further aspect of the present disclosure.

[0119] In one embodiment, the presently disclosed receiver 10, further comprises a mixer and a local oscillator, wherein the local oscillator is configured to adapt a frequency of a local oscillator signal based on the control signal of the presently disclosed device 20. Apparatus comprising the receiver

[0120] According to a further aspect, the present disclosure relates to an apparatus comprising the presently disclosed receiver. In a preferred embodiment, said apparatus is an internet of things, loT, device, or a smartwatch, or a user equipment (UE), or a wireless device, or a battery driven wireless device, or a power-aware wireless device.

[0121] Fig. 10 is a block diagram of a wake-up receiver 700 according to some embodiments of the present disclosure. In particular the wake-up receiver 700 is configured to detect a Binary Frequency Shift Keying (BFSK) modulated signal. A BFSK signal comprises a signal with a first frequency, for some periods of time and a second frequency for some other non overlapping periods of time. The first frequency may be corresponding to logic 1 and the second frequency to a logic 0. The wake-up receiver 700 down-converts the BSFK wake-up signal, RF signal, to IF frequency by means of a mixer (not shown) and a local oscillator (not shown) with a tunable local oscillator signal. The local oscillator may be a VCO.

[0122] The IF signal is delayed by a first tunable delay element 72 for obtaining a first delayed IF signal. A first XOR operation is performed by a first exclusive OR (XOR) gate 73 having the IF signal and the first delayed IF signal as input signals and having a first XOR signal as output signal. A first baseband signal is extracted by low-pass filtering the first XOR signal, by use of low-pass filter 78. The first baseband signal has a level peak in correspondence to a delay equal to half a period of the first frequency.

[0123] Similarly, the IF signal is delayed by a second tunable delay element 82 for obtaining a second delayed IF signal. A second XOR operation is performed by a second exclusive OR (XOR) gate 83 having the IF signal and the first delayed IF signal as input signals and having a first XOR signal as output signal. A second baseband signal is extracted by low-pass filtering the first XOR signal, by use of low-pass filter 88. The second baseband signal has a level peak in correspondence to a delay equal to half a period of the second frequency.

[0124] The values of the first and second delays corresponding to level peaks are related to each other by a frequency difference between the first and second frequency.

[0125] Control logic 77 may tune the tunable delay elements until level peaks are found. Level peaks are found by peak detector 75. In correspondence to found level peaks, baseband control logic 74 may use correlator 76 to correlate a third baseband signal with a known sequence. Third baseband signal may be one of: the first baseband signal, the second baseband signal or a combination of the first and second baseband signals. If the correlation is above or equal a second threshold, the correct sequence is found and the VCO settings may be retained or fine tuned to have an IF frequency corresponding to a desired delay value of the tunable delay element and corresponding to a desired IF frequency. If the correlation is below a second threshold the control logic 77 may send a signal to the VCO to change the frequency.

[0126] Method for BFSK wake-up signal

[0127] According to a further aspect, the present disclosure relates to a method for detection of a binary frequency shift modulated (BFSK) wake-up signal in a receiver, the method comprising: mixing a received signal with a local oscillator signal to obtain an intermediate frequency, IF, signal; obtaining a first delayed IF signal based on the IF signal, by use of a first tunable delay element 72; obtaining a second delayed IF signal based on the IF signal, by use of a second tunable delay element 82; obtaining a first exclusive OR, XOR, signal by use of a first XOR gate 73 having the IF signal and the first delayed IF signal as input signals and having the first XOR signal as output signal; obtaining a second exclusive OR, XOR, signal by use of a second XOR gate 83 having the IF signal and the second delayed IF signal as input signals and having the second XOR signal as output signal. The method further comprises; obtaining a first baseband signal based on the first XOR signal; obtaining a second baseband signal based on the second XOR signal; tuning the first tunable delay element 72 and the second tunable delay element 82 until a level peak of the first baseband signal is found and / or until a level peak of the second baseband signal is found; comparing a third baseband signal with a known sequence.

[0128] In the present section, whenever using the word “the second method” or “said second method” or “presently disclosed second method”, the reference is to the Method for BFSK wake-up signal according to a further aspect of the present disclosure.

[0129] In the presently disclosed method for BFSK wake-up signal, a BFSK wake-up signal is down-converted to an intermediate frequency signal IF by means of a mixer and a local oscillator. A wake-up signal may contain a sequence for wake-up and / or a sequence for synchronization.

[0130] The IF signal in the presently disclosed second method may have one of two frequencies for each logic period, that is for each digital time interval. A first frequency of a duration of a logic period corresponds to “logic 1” and a second frequency of a duration of a logic period corresponds to “logic 0”. The frequency shift or frequency difference between the first and the second frequency is known.

[0131] The presently disclosed second method may use two tunable delay elements. A first delay element may be used to obtain a first delayed IF signal. A second delay element may be used to obtain a second delayed IF signal. A first and a second XOR signals may be generated and low-pass filtered to a first and a second baseband signals. The first XOR signal may be obtained by logic XOR of the IF signal and the first delayed IF signal. The second XOR signal may be obtained by logic XOR of the IF signal and the second delayed IF signal. A first baseband signal may be obtained by low-pass filtering, or envelope detecting, the first XOR signal. A second baseband signal may be obtained by low-pass filtering, or envelope detecting, the second XOR signal. A first level of the first baseband signal may be detected using a first peak detector. Optionally a second level of the second baseband signal may be detected using a second peak detector. In order to detect the wake-up signal, both delays of the tunable delay elements may be tuned in correspondence to respective level peaks. That is a delay of the first delay element may be tuned in correspondence to a level peak of the first baseband signal. A delay of the second delay element may be tuned in correspondence to a level peak of the second baseband signal. A level peak of the first baseband signal may be found if the level of the first baseband signal is more than or equal to a first threshold. A level peak of the second baseband signal may be found if the level of the second baseband signal is more than or equal to a first threshold.

[0132] As the frequency shift, or frequency difference, between a “logic 0” and a “logic 1” is known the first and second delay that correspond to peaks of the first and second baseband signals have a known relation. For this reason, when a peak is found on, for example, the first baseband signal, the control logic may calculate a delay of the second tunable delay element that corresponds to a peak of the second baseband signal without using a second a peak detector, but relying on the first peak detector. Therefore the second peak detector is optional and the level peak of the second baseband signal may just be calculated based on the level peak of the first baseband signal, without comparison with the first threshold. Once the delays have been tuned in correspondence to level peaks, the first baseband signal may be compared or correlated to a known sequence. In one embodiment, once the delays have been tuned in correspondence to level peaks, the second baseband signal may be compared or correlated to a known sequence. In one embodiment, once the delays have been tuned in correspondence to level peaks, a combination of the first baseband signal and the second baseband signal may be compared or correlated to a known sequence. In one embodiment, any combination of the first baseband signal and the second baseband signal is compared or correlated to a known sequence. In one embodiment, a third baseband signal, which may be the first baseband signal, or the second baseband signal or a combination of the first baseband signal and the second baseband signal, is compared or correlated to a known sequence.

[0133] The IF signal, prior to being fed to the XOR gates and / or to the first and / or the second delay element, may be clipped by a clipper.

[0134] In one embodiment, the above disclosed second method further comprises outputting a control signal for tuning a frequency of the local oscillator signal, based on the comparison or correlation of the third baseband signal with the known sequence. The third baseband signal may be the first baseband signal, or the second baseband signal or a combination of the first baseband signal and the second baseband signal. This is advantageous to be able to control the frequency of the local oscillator in order to tune the wake-up receiver to a correct wake-up signal, that is to a wake-up signal carrying a known or pre-determined sequence

[0135] If the result of the comparison or the correlation is more than or equal to a second threshold, then the receiver is tuned to a correct wake-up signal and the VCO setting may be retained, that is the VCO may retain its output frequency, which is a frequency of the local oscillator, or fine tuned to have an IF frequency corresponding to a desired delay value of the tunable delay element and corresponding to a desired IF frequency.

[0136] If the result of the comparison or the correlation is below a second threshold, that may indicate that the receiver is tuned to a non-intended wake-up signal or is tuned to a non intended signal. Therefore the control signal may tune the frequency of the local oscillator to a different frequency. By non intended signal it is meant a signal that does not carry the known or pre-determined sequence.

[0137] The presently disclosed second method 130 (see e.g. Fig. 8) further comprises steps 131 - 136, wherein the peaks are level peaks of the third baseband signal.

[0138] The skilled person may realize that the presently disclosed second method, Method for BFSK wake-up signal, may comprise at least one or some or all of the steps of the presently disclosed method 300 or 130, Method for detection of a wake-up signal, according to the first aspect of the present disclosure, as shown in Fig. 7 and Fig. 8.

[0139] In particular, the presently disclosed second method, Method for BFSK wake-up signal, may comprise any of steps 301-306 in Fig. 7 and any of steps 131-136 in Fig. 8

[0140] Receiver for BFSK wake-up signal

[0141] According to a further aspect, the present disclosure relates to a receiver for receiving a binary frequency shift modulated (BFSK) wake-up signal, the receiver comprising: a local oscillator; a mixer having as output signal an intermediate frequency, IF, signal, the mixer having as input signals the wake-up signal and an output signal of the local oscillator; a first tunable delay element 72 for obtaining a first delayed IF signal; a first exclusive OR (XOR), gate 73 having the IF signal and the first delayed IF signal as input signals and having a first XOR signal as output signal; a first low-pass circuit 78, for obtaining a first baseband signal based on the first XOR signal; a second tunable delay element 82 for obtaining a second delayed IF signal; a second exclusive OR, XOR, gate 83 having the IF signal and the second delayed IF signal as input signals and having a second XOR signal as output signal; a second low-pass circuit 88, for obtaining a second baseband signal based on the second XOR signal; a first peak detector, PD, 75 for finding at least one level peak of at least one of the first and / or second baseband signal; control logic configured to: tune a delay of the first tunable delay element 72 and / or tune a delay of the second delay element 82 to find the at least one level peak of the at least one of the first and / or second baseband signal; and compare a third baseband signal with a known sequence, and wherein the third baseband signal is one of: the first baseband signal, the second baseband signal, and a combination of the first baseband signal and the second baseband signal. The presently disclosed Receiver for BFSK wake-up signal, may hereby denominated as BFSK WUS (Wake Up Signal) Receiver.

[0142] Fig. 10 is a block diagram of a BFSK WUS receiver 700, according to some embodiments of the present disclosure

[0143] The BFSK WUS Receiver may comprise: a local oscillator (not shown); a mixer (not shown) having as output signal an intermediate frequency, IF, signal.

[0144] With reference to Fig. 10, the presently disclosed BFSK WUS Receiver may optionally comprise a clipper 71 to clip the IF signal within between rails of digital supply voltage.

[0145] With reference to Fig.10 the BFSK WUS Receiver may comprise a first tunable delay element 72 to delay the IF signal by a first delay and obtain a first delayed IF signal; and a second tunable delay element 82 to delay the IF signal by a second delay and obtain a second delayed IF signal. The BFSK WUS Receiver may comprise a first XOR gate 73, having the IF signal and the first delayed IF signal as input signals and having a first XOR signal as output signal; and a first low-pass circuit (78), for obtaining a first baseband signal based on the first XOR signal.

[0146] The BFSK WUS Receiver may comprise a second XOR gate 83, having the IF signal and the second delayed IF signal as input signals and having a second XOR signal as output signal; and a second low-pass circuit (88), for obtaining a second baseband signal based on the second XOR signal.

[0147] A level of the first baseband signal may be detected by peak detector 75. The level of the first baseband signal may have a peak in correspondence to a delay of the tunable delay element which corresponds to a frequency representing, in one example, a “logic 1”. For example, if the period of the signal corresponding to “logic 1” is Tl, then a peak may be found in correspondence to a delay of the first delay element substantially equal to Tl / 2. Alternatively, the level of the first baseband signal has a peak in correspondence to a delay of the tunable delay which correspond to a frequency representing, for example, a “logic 0”. It is a design choice to choose if the first tunable delay should be tuned to a first or a second frequency of the BFSK WUS.

[0148] As the frequency shift or difference between a “logic 0” and a “logic 1” is known, the first and second delay that correspond to level peaks of the first and second baseband signals will have a known relation to each other. For this reason, in one embodiment, when a peak is found on, for example, the first baseband signal, the control logic may calculate a delay of the second tunable delay element that corresponds to a peak of the second baseband signal without using a second a peak detector, but relying on the first peak detector. Therefore the second peak detector is optional.

[0149] The BFSK WUS Receiver comprises control logic configured to: tune a delay of the first tunable delay element 72 and tune a delay of the second delay element 82 to find at least one level peak of a third baseband signal; and compare the third baseband signal with a known sequence, and wherein the third baseband signal is one of: the first baseband signal, the second baseband signal, and a combination of the first baseband signal and the second baseband signal. With reference to Fig. 10, the control logic may be represented by block 77, 76, 74, or combination thereof. In particular block 76 may represent a circuit for comparing the received sequence with a known sequence. In one embodiment, block 76 may be a correlator configured to correlate a third baseband signal with a known sequence.

[0150] In one embodiment the third baseband signal may be the first baseband signal.

[0151] In another embodiment the third baseband signal may be the second baseband signal.

[0152] In another embodiment the third baseband signal may be a combination of the first and the second baseband signal. Control logic 74 may be configured for combining the first baseband signal and the second baseband signal.

[0153] Fig. 11 illustrates one embodiment of the presently disclosed BFSK receiver., in this embodiment, the presently disclosed device, may further comprise a second peak detector 85 to detect level peaks of the second baseband signal. In this embodiment, a level peak of the second baseband signal may be found using the second peak detector 85.

[0154] With reference to Fig.11, in one embodiment the BFSK WUS Receiver may comprise a further or second peak detector (85) to measure a level of the second baseband signal. In this embodiment, the control logic can use the level measured by the second peak detector to identify delays of the second delay element in correspondence of which a level peak of the second baseband signal is present.

[0155] With reference to Fig.11, in one embodiment the BFSK WUS Receiver may comprise a further correlator 86 to correlate the second baseband signal with a known sequence.

[0156] The BFSK WUS Receiver may be configured to carry out the presently disclosed second method, Method for BFSK wake-up signal.

[0157] The BFSK WUS Receiver may be configured to carry out the presently disclosed method 300, Method for detection of a wake-up signal, according to the first aspect of the present disclosure.

[0158] The BFSK WUS Receiver may be configured to carry out any combination of the presently disclosed second method, Method for BFSK wake-up signal, and the presently disclosed method 300, Method for detection of a wake-up signal, according to the first aspect of the present disclosure.

[0159] Apparatus comprising the receiver for BFSK wake-up signal

[0160] According to a further aspect, the present disclosure relates to an apparatus comprising the presently disclosed receiver for BFSK wake-up signal. In a preferred embodiment, said apparatus is an internet of things, loT, device, or a smartwatch, or a user equipment (UE), or a wireless device, or a battery driven wireless device, or a power-aware wireless device.

Claims

CLAIMS1. A method (300) for detection of a wake-up signal in a receiver (10), the method comprising: mixing a received signal with a local oscillator signal to obtain an intermediate frequency, IF, signal; obtaining a delayed IF signal based on the IF signal, by use of a tunable delay element (22); obtaining an exclusive OR, XOR, signal by use of an XOR gate (23) having the IF signal and the delayed IF signal as input signals and having the XOR signal as output signal; obtaining a baseband signal based on the XOR signal; tuning the tunable delay element (22) until at least one level peak of the baseband signal is found; and comparing the baseband signal with a known sequence.

2. The method according to claim 1, further comprising outputting a control signal for tuning a frequency of the local oscillator signal, based on the comparison of the baseband signal with the known sequence and / or based on a value of the tunable delay element.

3. The method according to any one of the preceding claims, wherein the wake-up signal is an On / Off keying modulated signal.

4. The method according to any one of the preceding claims, wherein the at least one level peak of the baseband signal is found when a level of the baseband signal is more than or equal to a first threshold.

5. The method according to any one of the preceding claims, further comprising tuning a delay of the delay element if a level of the baseband signal is below a first threshold.

6. The method according to any one of the preceding claims, wherein the wake-up signal is detected when the baseband signal at least partly matches the known sequence.

7. The method according to any one of the preceding claims, wherein comparing the baseband signal with a known sequence comprises correlating the baseband signal with the known sequence.

8. The method according to claim 7, further comprising tuning a frequency of the local oscillator signal if the correlation of the baseband signal with the known sequence is below a second threshold, or if a difference between a delay of the delay element and a desired delay value is greater than a third threshold.

9. The method according to any one of the preceding claims, wherein the IF signal is clipped between rails of a digital supply voltage before being fed to the tunable delay element and / or to the XOR gate.

10. The method according to any one of the preceding claims, further comprising sweeping a delay of the tunable delay element to obtain the at least one level peak of the baseband signal.

11. The method according to claims 8 and 10, further comprising obtaining a correlation value in correspondence to one or more of the at least one level peak and, if all the obtained correlation values are below the second threshold, tuning the frequency of the local oscillator signal, otherwise not tuning the frequency of the local oscillator signal.

12. The method of claim 11, wherein tuning the frequency of the local oscillator signal is done in steps.

13. The method according to any one of claims 11-12, wherein tuning the frequency of the local oscillator signal comprises starting from selecting a center frequency of the variable oscillator and then following an alternating pattern on a higher and a lower side of the center frequency, said alternating pattern progressively moving from the center frequency to frequencies progressively further away from the center frequency.

14. A device (20) having as input signal an intermediate frequency, IF, signal, the device comprising: a tunable delay element (22) for obtaining a delayed IF signal;an exclusive OR, XOR, gate (23) having the IF signal and the delayed IF signal as input signals and having an XOR signal as output signal; a first circuit (28), for obtaining a baseband signal based on the XOR signal; a second circuit (26) for obtaining a comparison of the baseband signal with a known sequence; control logic configured to: tune a delay of the tunable delay element (22) to find at least one level peak of the baseband signal, and a peak detector, PD, (25) for detecting said at least one level peak of the baseband signal.

15. The device according to claim 14, wherein the second circuit for obtaining the comparison is a correlator and the comparison is a correlation.

16. The device according to any one of claims 14-15, further comprising a signal clipper(21) to clip the IF signal before the IF signal is fed to an input of the XOR gate and / or to an input of the tunable delay element (22).

17. The device according to any one of claims 14-16, wherein the first circuit is a low-pass filter or an envelope detector.

18. The device according to any one of claims 14-17, wherein the tunable delay element(22) comprises passive and / or active components.

19. The device according to any one of claims 14-18, wherein the control logic is further configured to, based on the comparison of the baseband signal with a known sequence, output a control signal (29).

20. The device according to claim 19, wherein a frequency of a local oscillator signal, is tuned based on the control signal.

21. A receiver (10) comprising the device (20) of claims 14-20.

22. The receiver (10) of claim 21, further comprising a mixer and a local oscillator, wherein the local oscillator is configured to adapt a frequency of a local oscillator signal based on the control signal of the device (20).

23. The receiver according to claim 22, configured to perform the method according to any one of claims 1-13.

24. A method for detection of a binary frequency shift modulated, BFSK, wake-up signal in a receiver, the method comprising: mixing a received signal with a local oscillator signal to obtain an intermediate frequency, IF, signal; obtaining a first delayed IF signal based on the IF signal, by use of a first tunable delay element (72); obtaining a second delayed IF signal based on the IF signal, by use of a second tunable delay element (82); obtaining a first exclusive OR, XOR, signal by use of a first XOR gate (73) having the IF signal and the first delayed IF signal as input signals and having the first XOR signal as output signal; obtaining a second exclusive OR, XOR, signal by use of a second XOR gate (83) having the IF signal and the second delayed IF signal as input signals and having the second XOR signal as output signal; obtaining a first baseband signal based on the first XOR signal; obtaining a second baseband signal based on the second XOR signal; tuning the first tunable delay element (72) and / or the second tunable delay element (82) until a level peak of the first baseband signal is found and / or until a level peak of the second baseband signal is found; comparing a third baseband signal with a known sequence.

25. The method according to claim 24, wherein the third baseband signal is one of: the first baseband signal, the second baseband signal, and a combination of the first baseband signal and the second baseband signal.

26. The method according to claims 24-25, wherein comparing a third baseband signal with a known sequence comprises correlating the third baseband signal with the known sequence by use of at least one correlator (76, 86).

27. The method according to claims 24-26, further comprising outputting a control signal for tuning a frequency of the local oscillator signal, based on the comparison of the third baseband signal with the known sequence.

28. A receiver for receiving a binary frequency shift modulated, BFSK, wake-up signal, the receiver comprising: a local oscillator; a mixer having as output signal an intermediate frequency, IF, signal, the mixer having as input signals the wake-up signal and an output signal of the local oscillator; a first tunable delay element (72) for obtaining a first delayed IF signal; a first exclusive OR, XOR, gate (73) having the IF signal and the first delayed IF signal as input signals and having a first XOR signal as output signal; a first low-pass circuit (78), for obtaining a first baseband signal based on the first XOR signal; a second tunable delay element (82) for obtaining a second delayed IF signal; a second exclusive OR, XOR, gate (83) having the IF signal and the second delayed IF signal as input signals and having a second XOR signal as output signal; a second low-pass circuit (88), for obtaining a second baseband signal based on the second XOR signal; a first peak detector, PD, (75) for finding at least one level peak of at least one of the first and / or second baseband signal; control logic configured to:- tune a delay of the first tunable delay element (72) and / or tune a delay of the second delay element (82) to find the at least one level peak of the at least one of the first and / or second baseband signal; compare a third baseband signal with a known sequence,wherein the third baseband signal is one of: the first baseband signal, the second baseband signal, and a combination of the first baseband signal and the second baseband signal.

29. The receiver of claim 28, the receiver configured to perform the steps according to claims 24-27.

30. An apparatus comprising the receiver (10) according to any one of claims 22-23.

31. The apparatus of claim 30, the apparatus being an internet of things, loT, device, or a smartwatch, or a user equipment (UE), or a wireless device, or a battery driven wireless device, or a power-aware wireless device.

32. An apparatus, comprising the receiver (120) according to claim 28-29.

33. The apparatus of claim 32, the apparatus being an internet of things, loT, device, or a smartwatch, or a user equipment (UE), or a wireless device, or a battery driven wireless device, or a power-aware wireless device.

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