Method and device for demodulating an RF signal

Abstract

The present invention discloses a method and device for demodulating an RF signal to polar in-phase and quadrature ( IQ) components in a wearable device that monitors vital functions of a user. The method includes receiving the RF signal through an instrumentational amplifier and processing output signals from the amplifier for sequentially extracting the I signals and the Q signals with a 90 ° delay between the extraction of I signals and Q signals. The device comprises a logical circuit configured to receive RF input signals, process the input signals using a logical operation, and provide output signals based on the logical operation. The digital I / Q demodulation is achieved using a SINC filter, a deltasigma modulator, and a digital filter with bandwidth larger than the modulated signal frequency. The wearable device ' s clock is used as a base signal for the digital I / Q demodulator. This invention offers a novel, cost-effective, and efficient solution for monitoring vital functions in wearable devices.

Description

[0001] Method and Device for Demodulating an RF Signal

[0002] DESCRIPTION

[0003] Technical background of the invention

[0004] The invention relates to a method for demodulating an RF Signal . Speci fically, the present invention relates to a method for demodulating an RF Signal having a signal frequency and / or mixed with a local oscillator signal to polar in-phase and quadrature ( IQ) components . The invention further relates to a logical circuit to perform such demodulation, and to a wearable device comprising such a logical circuit . In particular, the present invention relates generally to the field of wearable devices , and more particularly to the demodulation of radio frequency (RF) signals used for bio-impedance measurements in wearable devices , such as smartwatches , to monitor vital functions of a user .

[0005] Background

[0006] In recent years , wearable devices such as smart watches or sports tracker devices have become increasingly popular for monitoring various vital functions of users , such as heart rate , blood pressure , and other health-related parameters . These devices typically utili ze bio-impedance spectroscopy to measure and monitor these vital functions . In such systems , bio-impedance is measured by RF signals . To achieve high- quality measurements in these or other, general measurement applications such as in Hall-Sensors , the RF signals are typically in-phase and quadrature ( I / Q) modulated and need to be demodulated .

[0007] Conventional methods for demodulating I / Q modulated RF signals include using analog systems , such as I-mixers and Q- mixers . In particular, in such systems two matched demodulator circuits may be used to convert the RF input signal directly to baseband analog I and Q signals that are subsequently converted to digital data . The functionality of this circuit is based upon the RF input signal being split and mixed with two local oscillator signals that have a phase shi ft between them . This phase shi ft provides the mechanism to distinguish the I and Q components of the RF signal . The mixer outputs then are lowpass filtered to remove the high- frequency mixing products , providing baseband analog I and Q signals that are sampled and converted to digital values . However, analog demodulation methods have various drawbacks , including di f ferent gain for I and Q signals , which results in larger errors . The nature of the conventional analog I / Q detector makes it susceptible to errors associated with gain matching, DC of fsets , quadrature phase errors , carrier leakage , and impedance matching . These errors can be di f ficult to completely eliminate or compensate for, causing RF measurement errors .

[0008] To improve the accuracy of demodulation, digital demodulation methods have been developed . However, digital demodulation typically requires the use of an atan function, which can be computationally intensive .

[0009] Traditional methods for addressing the problems associated with analog and digital demodulation have focused on improving the performance of the individual components involved in the demodulation process . For example , ef forts have been made to improve the accuracy of evaluation of the atan function or to develop alternative functions that can be used in digital demodulation . However, these approaches do not fully address the underlying issues associated with demodulation ef ficiency and accuracy .

[0010] In the prior art , US20230224199A1 discloses a method and apparatus for demodulating I / Q signals using a digital signal processor . US20180372870A1 discloses a method and system for demodulating I / Q signals using a complex mixer . While these prior art references provide solutions for demodulating I / Q signals , they do not adequately address the issues of demodulation ef ficiency and accuracy, particularly in the context of wearable devices that require low power consumption and compact design .

[0011] There is a need to develop a more ef ficient and accurate method for demodulating RF signals , in particular for the intended use in wearable devices , that overcomes the limitations of the existing analog and digital demodulation methods . In particular, there is a need for a demodulation method that can be implemented in a compact , low-power wearable device without sacri ficing accuracy or increasing computational complexity .

[0012] Summary

[0013] The primary obj ective of the present invention is to provide a method for demodulating an RF signal to polar in-phase and quadrature ( IQ) components using digital I / Q demodulation . Another obj ective of the present invention is to implement the method in a wearable device for monitoring vital functions of a user . Yet another obj ective of the present invention is to utili ze a clock as a base signal for the digital I / Q demodulator .

[0014] According to one aspect of the present invention, a method for demodulating an RF signal to polar in-phase and quadrature ( IQ) components is provided . The method includes receiving the RF signal , having a signal frequency and / or mixed with a local oscillator signal , through an instrumentational ampli fier, converting the output signal of the instrumental ampli fier into a digital data stream in an analog-to-digital converter, and sequentially extracting the I signals and the Q signals by filtering the converted data stream or the modulator data stream . In a preferred embodiment , converting the output signal of the instrumental ampli fier into a digital data stream is ef fected in a delta sigma modulator .

[0015] In one aspect of the invention, a Q signal is extracted from the converted data stream at a 90 ° + n* 180 ° delay of the RF signal or the local oscillator signal as compared to the extraction of an I signal from the converted data stream . An alternative aspect of the invention suggests a method wherein, as compared to the extraction of a first I signal ( I I ) from the converted data stream, a first Q signal ( QI ) is extracted from the converted data stream at a 45 ° delay of the RF signal and / or the local oscillator signal , a second I signal ( 12 ) is extracted from the converted data stream at a 90 ° delay of the RF signal and / or the local oscillator signal , and a second Q signal ( Q2 ) is extracted from the converted data stream at a 135 ° delay of the RF signal and / or the local oscillator signal , wherein the I signal is derived as the di f ference between the first and the second I signals ( I I , 12 ) , and the Q signal is derived as the di f ference between the first and the second Q signals ( QI , Q2 ) .

[0016] Preferred embodiments of the invention are subj ect of the dependent claims .

[0017] The invention is based on the consideration that a digital I / Q demodulation of the RF signal may be achieved by first converting the complete signal into a digital data stream and using RF signal or the local oscillator signal , respectively, as a framework to adj ust the sampling of the signal such that both the I and Q signals can be extracted from the digital data stream by appropriate timing of the starting and / or filtering of the converted or modulated digital data stream . In particular, sampling of the data representing the Q signal with respect to the RF signal or the local oscillator signal may be postponed by 90 ° as compared to the sampling of the data representing the I signal . In other words , since for I and Q signals the sin and cos functions should be measured, as a first aspect a cosinus signal may be measured with a Delta-sigma modulator followed by a digital filter the bandwidth of which should be larger than the modulated signal frequency . The measurement of the sinus signals then may be started at a delay of 90 ° or some delay 90 ° +n* 180 ° with reference to the start of the cosinus conversion time . In other embodiments , in particular i f of fsets need to be accounted for, measurements with 45 ° delay may be used with phases of Ql=45 ° , 11=90 ° , Q2=135 , and 12=180 ° , in which the respective values may be calculated as 1=11- 12 and Q=Q1-Q2 .

[0018] According to another aspect of the present invention, the RF signal is generated by bio-impedance measurements . In some embodiments , the RF signal is generated by a wearable device from a user . The wearable device may be configured to monitor vital functions of the user .

[0019] In certain embodiments , the method further comprises providing the local oscillator signal as a base signal for the digital I / Q demodulator using a clock . The clock providing the base signal for the digital I / Q demodulator may be part of the wearable device , preferably the integrated clock of the wearable device .

[0020] A logical circuit , in one aspect as represented in a block- diagram, is also provided in the present invention . The logical circuit is configured to receive RF input signals , process the input signals using a logical operation, and provide output signals based on the logical operation . The logical operation may be performed by a digital I / Q demodulator . In an aspect of the invention, the logical circuit as represented by said block-diagram comprises an instrumental ampli fier having an output , said output being connected with an analog- to-digital converter, and further an I / Q extraction module , wherein said extraction module is configured to sample the output signal of the instrumental ampli fier in response to an input RF Signal having a signal frequency and / or mixed with a local oscillator signal with the analog-to-digital converter, and sequentially extract the I signals and the Q signals from the converted data stream, wherein a Q signal is extracted from the converted data stream at a 90 ° + n* 180 ° delay of the RF signal or local oscillator signal as compared to the extraction of an I signal from the converted data stream . In an alternative aspect of the invention, the logical circuit comprises an instrumental ampli fier having an output , said output being connected with an analog-to-digital converter, and further an I / Q extraction module , wherein said extraction module is configured to sample the output signal of the instrumental ampli fier in response to an input RF Signal having a signal frequency and / or mixed with a local oscillator signal with the analog-to-digital converter, and sequentially extract the I signals and the Q signals from the converted data stream, wherein, as compared to the extraction of a first I signal ( I I ) from the converted data stream, a first Q signal ( QI ) is extracted from the converted data stream at a 45 ° delay of the RF signal or the local oscillator signal , a second I signal ( 12 ) is extracted from the converted data stream at a 90 ° delay of the RF signal or the local oscillator signal , and a second Q signal ( Q2 ) is extracted from the converted data stream at a 135 ° delay of the RF signal or the local oscillator signal , wherein the I signal is derived as the di f ference between the first and the second I signals ( I I , 12 ) , and the Q signal is derived as the di fference between the first and the second Q signals ( QI , Q2 ) .

[0021] In some embodiments , the logical circuit is part of a wearable device . The wearable device may be configured to monitor vital functions of a user . The clock providing the base signal for the digital I / Q demodulator may be part of the wearable device .

[0022] Main advantages of the present invention may be seen in that by the principle concept of first converting the RF signal into a converted digital data stream and performing the actual I / Q demodulation in a subsequent step, the I / Q demodulation may be ef fected on a digital basis in a very reliable yet simple way, while having low requirements for the hardware equipment .

[0023] The foregoing paragraphs have been provided by way of general introduction and are not intended to limit the scope of the following claims . The described embodiments , together with further advantages , will be best understood by reference to the following detailed description taken in conj unction with the accompanying drawings .

[0024] Brief Description of the Preferred Embodiments

[0025] Preferred embodiments and aspects of the invention are described further in connection with a drawing . In this drawing,

[0026] FIG . 1 shows a wearable device , in particular a smartwatch;

[0027] FIG . 2 schematically shows a logic circuit of the wearable device of FIG . 1 ;

[0028] FIG . 3 schematically shows a signal pattern for digital I / Q demodulation; and

[0029] FIG . 4 schematically shows an alternative signal pattern for digital I / Q demodulation .

[0030] It is to be understood that both the foregoing general description and the following detailed description are merely exemplary, and are intended to provide an overview or framework to understand the nature and character of the claims . The accompanying drawings are included to provide a further understanding and are incorporated in, and constitute a part of , this description . The drawings illustrate one or more embodiments , and together with the description serve to explain principles and operation of the various embodiments . In the drawings , identical parts are labelled by the same reference numerals .

[0031] Detailed Description of the Preferred Embodiments

[0032] The present disclosure will now be described more fully hereinafter with reference to the accompanying drawings showing embodiments of the disclosure . The disclosure may, however, be embodied in many di f ferent forms and should not be con- strued as limited to the embodiments set forth herein . Rather, these embodiments are provided so that the disclosure will fully convey the scope of the disclosure to those skilled in the art . The drawings are not necessarily drawn to scale but are configured to clearly illustrate the disclosure .

[0033] FIG . 1 shows an example of a wearable electronic device 1 , in particular a smartwatch . It is noted that this embodiment is shown as a preferred example of an application in which the present invention may be used . Other applications , however, are possible , such in high-accuracy measurement systems like Hall sensors , e . g .

[0034] In general , the electronic device 1 as shown in FIG . 1 can correspond to any form of electronic wearable device , a portable media player, a media storage device , a portable digital assistant ( PDA) , a tablet computer, a computer, a mobile communication device , a GPS unit , a remote control device , or other electronic device . The electronic device 1 can be referred to as an electronic device , or a consumer device . In some examples , the electronic device 1 can include a housing 2 that can carry operational components , for example , in an internal volume at least partially defined by the housing . The electronic device 1 in the embodiment shown can also include a strap 4 or other retaining component that can secure the device 1 to a body of a user as desired . The electronic device 1 also may include a display assembly 6 attached to the housing 2 . The display assembly 6 can include a glass , a plastic, or any other substantially transparent exterior layer, material , component , or assembly . The display assembly 6 can include multiple layers , with each layer providing a unique function . Accordingly, the display assembly 6 can be , or can be a part of , an interface component .

[0035] The display assembly 6 can define a front exterior surface of the device 1 and, as described herein, this exterior surface can be considered an interface surface . In some examples , the interface surface defined by display assembly 6 can receive inputs , such as touch inputs , from a user . In other words , the display assembly 6 can include a touch sensitive layer, or form a touch interface , configured to receive touch inputs from a user .

[0036] In some examples , the housing 2 can be a substantially continuous or unitary component and can define one or more openings to receive components of the electronic device 1 . In some examples , the device 1 can include input components such as one or more buttons 8 and / or a crown 10 that can be disposed in the openings . In some examples , a material can be disposed between the buttons 8 and / or crown 10 and the housing 2 to provide an airtight and / or watertight seal at the locations of the openings . The housing 2 can also define one or more openings or apertures , such as aperture 12 that can allow for sound to pass into or out of the internal volume defined by the housing 2 . For example , the aperture 12 can be in communication with a microphone component disposed in the internal volume . In some examples , the housing 2 can define or include a feature , such as an indentation to removably couple the housing 2 and a strap or retaining component .

[0037] Among other components or modules designed for individual functionalities , the electronic device 1 comprises a module 20 for monitoring vital functions of the user . For this purpose , module 20 is designed to measure or monitor the bioimpedance of the user . Module 20 comprises a logic circuit 22 which is shown schematically in FIG . 2 .

[0038] The electronic device 1 comprises a current excitation source 30 which is coupled to the skin 32 of the user by electrodes 34 i f the user wears the electronic device 1 in physical contact . In consequence , in the circuit 22 as shown this contact will be detected in the form of the bio-impedance Z of the user . The current excitation provided by source 30 is delivered in the form of a sinusoidal signal . In reaction, the bioimpedance Z may then be detected by electrodes 36 . The respective signal , in the form of an RF signal generated in response to the current excitation signal as local oscillator signal , is fed into an instrumentational ampli fier 40 which on its output is connected to a Delta-Sigma analog-to-digital converter 42 via a filter 44 . In the Delta-Sigma analog-to- digital converter 42 , the output signal of the instrumental ampli fier 40 may be sampled .

[0039] It is noted that due to the principle design of the circuit 22 as explained below, filter 44 may be designed as antialiasing filter, enabling quick response times and high reliability . In comparison, in previous systems , low pass filters might need to be used instead, providing much higher and thus slower response times .

[0040] The instrumentational ampli fier 40 thus in the wearable device 1 is responsible for receiving the RF signal , having the same signal frequency as the current excitation signal . The detected RF signal is processed through the instrumentational ampli fier 40 , ampli fying the di f ference between the input signals . The ampli fied signal is then ready for further processing .

[0041] Following the ampli fication process , the output signal of the instrumentational ampli fier 40 , after having been passed through the anti-aliasing filter 44 is converted into a digital data stream in the analog-to-digital converter 42 . The anti-aliasing filter 44 in particular may be provided in order to filter higher order harmonics of the excitation signal . The converter 42 trans forms the analog signal into a digital format , making it suitable for sampling or further processing by the digital I / Q demodulator . The digital I / Q demodulator is a key component in the circuit 22 and is responsible for the demodulation of the RF signal . It operates by sequentially extracting the I signals and the Q signals from the converted data stream .

[0042] The extraction process , for two alternative scenarios , is represented schematically in Figs . 3 and 4 . Figs . 3 and 4 each show a signal pattern 50 , 52 for digital I / Q demodulation, respectively . The I / Q demodulation process in both al- ternatives shown involves a speci fic delay of the sampling steps for the various signal components .

[0043] FIG . 3 shows the signal pattern 50 for the sampling signal with the reference frequency fR which is an oscillating signal in sync with the current excitation signal of device 1 . Sampling of the I signal in this embodiment is started at starting time TO I which is chosen in sync with a period of reference frequency fR . Sampling of the I signal in this embodiment , in view of the properties of the various components including their delay times etc, is maintained over some cycles , providing a sampling or conversion interval as represented by box 60 . For extraction of the Q signal , in this embodiment , an appropriate delay with respect to the sampling signal or the local oscillator signal is chosen, such that a Q signal is extracted from the converted data stream at a 90 ° + n* 180 ° delay as compared to the extraction of an I signal from the same data stream . Thus , the starting time TOQ for sampling the Q signal is chosen accordingly as indicated in FIG . 3 . In FIG . 3 , this is represented in the signal pattern 50 by the Q-signal sampling signal fR90 , which in comparison to the sampling signal fR is shi fted by 90 ° . Sampling of the Q signal in this embodiment , in view of the properties of the various components including their delay times etc, also is maintained over some cycles , providing a sampling or conversion interval as represented by box 62 .

[0044] In certain cases , the extraction of the signals involves a more complex process . For instance , the output signal delivered by the delta-sigma ADC 42 may comprise an of fset . In order to include this into the demodulation process , as represented by the signal pattern 52 shown in FIG . 4 , sampling of a first component of the I signal in this embodiment is also started at starting time T0 I 1 which is chosen in sync with a period of sampling signal fR . For extraction of further information, as compared to the extraction of the first I signal ( I I ) from the converted data stream, a first Q signal (QI ) is extracted from the data stream at a 45 ° delay of the sampling signal or the local oscillator signal . Following this, a second I signal (12) is extracted from the data stream at a 90° delay of the sampling signal or the local oscillator signal, and a second Q signal (Q2) is extracted from the data stream at a 135° delay of the sampling signal or the local oscillator signal. Thus, the starting times T0Q1, T0I2, and T0Q2 for sampling the respective I / Q signals are chosen accordingly as indicated in FIG. 4. The final I and Q signals are derived from the differences between these extracted signals, with 1=11-12 and Q=Q1-Q2.

[0045] Sampling of the I and Q signals in this embodiment, in view of the properties of the various components including their delay times etc, also is maintained over some cycles, providing a sampling or conversion interval as represented by boxes 64, 66, 68, 70.

[0046] It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit or scope of the disclosure as laid down in the appended claims. Since modifications, combinations, sub-combinations and variations of the disclosed embodiments incorporating the spirt and substance of the disclosure may occur to the persons skilled in the art, the disclosure should be construed to include everything within the scope of the appended claims.

[0047] LIST OF REFERENCE NUMERALS

[0048] 1 wearable device

[0049] 2 housing

[0050] 4 strap

[0051] 6 display assembly

[0052] 8 buttons

[0053] 10 crown

[0054] 12 aperture

[0055] 20 module

[0056] 22 logical circuit

[0057] 30 current excitation source

[0058] 32 skin

[0059] 34, 36 electrodes

[0060] 40 instrumentational amplifier

[0061] 42 analog-digital converter

[0062] 44 filter

[0063] 50, 52 signal pattern

[0064] 60, 62, 64,

[0065] 66, 68, 70 box

[0066] T0I starting time

[0067] TOQ starting time

[0068] T0I1 starting time

[0069] T0I2 starting time

[0070] T0Q1 starting time

[0071] T0Q2 starting time

Claims

CLAIMS1. A method for demodulating an RF Signal having a signal frequency to polar in-phase and quadrature (IQ) components, the method comprising:- receiving the RF signal through an instrumentational amplifier (40) ;- converting the output signal of the instrumental amplifier (40) to a converted data stream in an analog-to-digital converter ( 42 ) , and- sequentially extracting the I signals and the Q signals by filtering the converted data stream.

2. The method of claim 1, wherein a Q signal is extracted from the converted data stream by sampling at a 90° + n*180° delay of the RF signal as compared to the extraction of an I signal from the converted data stream.

3. The method of claim 1, the method further comprising:- sequentially extracting the I signals and the Q signals by sampling the converted data stream, wherein, as compared to the extraction of a first I signal (II) from the converted data stream, a first Q signal (QI) is extracted from the converted data stream at a 45° delay of the RF signal, a second I signal (12) is extracted from the converted data stream at a 90° delay of the RF signal, and a second Q signal (Q2) is extracted from the converted data stream at a 135° delay of the RF signal, wherein the I signal is derived as the difference between the first and the second I signals (II, 12) , and the Q signal is derived as the difference between the first and the second Q signals (QI, Q2 ) .

4. The method of any one of claims 1 to 3, wherein the RF signal is generated by bio-impedance measurements.

5. The method of any one of claims 1 to 4, wherein the RF signal is generated in a wearable device (1) from a user.

6. The method of claim 5, wherein the wearable device (1) is configured to monitor vital functions of the user.

7. The method of any one of claims 1 to 5, further comprising providing a local oscillator signal for the digital I / Q demodulation using a clock.

8. The method of claim 7, wherein the clock providing the local oscillator signal for the digital I / Q demodulator is an integrated clock of the wearable device (1) .

9. A logical circuit (22) comprising an instrumental amplifier (40) having an output, said output being connected with an analog-to-digital converter (42) , and further comprising an I / Q extraction module, wherein said extraction module is configured to:- convert the output signal of the instrumental amplifier(40) in response to an input RF Signal into a converted data stream in the analog-to-digital converter (42) , and- sequentially extract the I signals and the Q signals from the converted data stream, wherein a Q signal is extracted from the converted data stream at a 90° + n*180° delay of the RF signal as compared to the extraction of an I signal from the converted data stream.

10. A logical circuit (22) comprising an instrumental amplifier (40) having an output, said output being connected with an analog-to-digital converter (42) , and further comprising an I Q extraction module, wherein said extraction module is configured to:- convert the output signal of the instrumental amplifier(40) in response to an input RF Signal into a converted data stream in the analog-to-digital converter (42) , and- sequentially extract the I signals and the Q signals from the converted data stream, wherein, as compared to the extraction of a first I signal (II) from the converted data stream, a first Q signal (QI) is extracted from the converted data stream at a 45° delay of the RF signal, a second I signal (12) is extracted from the converted data stream at a 90°delay of the RF signal, and a second Q signal (Q2) is extracted from the converted data stream at a 135° delay of the RF signal, wherein the I signal is derived as the difference between the first and the second I signals (II, 12) , and the Q signal is derived as the difference between the first and the second Q signals (QI, Q2 ) .

11. User-wearable device (1) comprising a logical circuit(22) according to claim 9 or 10.

12. The device of claim 11, wherein the wearable device (1) is configured to monitor vital functions of a user.

13. The device (1) of claim 11 or 12, further comprising an internal clock, wherein said clock is used to provide the local oscillator signal for the digital I / Q demodulator.

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