FIELD OF THE INVENTION

The invention relates to a receiver module and a transceiver module for use in a body coupled communication device.

The invention further relates to a method of receiving signals via a body transmission channel in a receiver module of a body coupled communication device.

BACKGROUND OF THE INVENTION

It has been shown over the last few years that body coupled communications (BCC) is a viable alternative to radio frequency (RF) based communications in body-area network (BAN) and user identification applications. In BCC, signals are conveyed over the body instead of through the air. As such, the communication is confined to an area around the body in contrast to RF communications, where a much larger area is covered. Therefore, communication is only possible between devices situated on, connected to, or placed close to the body.

In BCC the signals are transmitted via couplers, which are placed near or on the body. The couplers are electrodes or metal plates. These couplers transfer the data signal, either galvanically or capacitively, to the body. The transfer characteristic of the body channel is shown to be optimal for frequencies from about 100 kHz up to about 100 MHz. Given the characteristic of the body channel and the bandwidth of interest, an interesting solution for BCC proved to be the direct coupling to the human body of digital wideband signals, without any kind of modulation or up conversion. An approach for receiving digital wideband signals for body coupled communication was introduced in published patent application WO2010/049842 which is incorporated by reference.

Patent application WO2010/049842 discloses a communication apparatus, method and computer program product for providing a reception approach in a body coupled communication system with a switch-based filtering in order to remove low frequency interference and noise without attenuating the wanted digital signal. The document also discloses a receiver structure that makes use of correlation for both data detection and synchronization in order to suppress the uncorrected interference without attenuating the wanted signal.

The solution of WO2010/049842 comprises at the input of a BCC receiver a switched-based high-pass filter which couples and decouples the couplers of the BCC receiver to each other in dependence of a control signal. Subsequently the filtered received signal is amplified and then correlated with a template signal that should be as closely identical as possible with the expected incoming signal to lead to a beneficial suppression of every received signal component that is not wanted (e.g. noise or interference). This system works properly when a good synchronization is guaranteed. This is enabled by another correlation block that performs the correlation between the incoming signal and a

synchronization pattern.

Although the switched-based high-pass filter of the prior art solution reduces impact of low- frequency noise and interferers, in practice, the switching is accompanied by artifacts that degrade the performance of the receiver. Furthermore, interference is suppressed relatively well in so far this interference relates to the actual transmission of data between the couplers of a transmitter and the couplers of a receiver. Inside the receiver noise and interference may also be introduced in the BCC operation frequency band and the solution of the cited patent application provides only a limited suppression of these types of interfering signals.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a body coupled communication receiver or transceiver which is better capable of suppressing noise and interference signals.

A first aspect of the invention provides a receiver module. A second aspect of the invention provides a transceiver module. A third aspect of the invention provides a method of receiving signals via a body transmission channel in a receiver module of a body coupled communication device. Advantageous embodiments are defined in the dependent claims.

A receiver module for a body coupled communication device and for receiving signals via a body transmission channel in accordance with the first aspect of the invention comprises two couplers, a differential band-pass amplifier and a differential correlator. The two couplers are for receiving signals from the body transmission channel which follows a body of a user when the body is in the direct vicinity of the couplers. The differential bandpass amplifier has a differential output and is directly coupled to the two couplers for amplifying within a specific spectral range a differential voltage and are present between the two couplers to obtain an amplified differential signal. The differential correlator

arrangement synchronizes a receiver module timing with the amplified differential signal based on a first correlation between the amplified differential signal and a synchronization signal and decodes the amplified differential signal to a received digital signal by performing a second correlation between the amplified differential signal and the receiver module timing.

In the prior art, one of the couplers is coupled to a ground voltage of the receiver module and only a voltage induced on the second coupler is provided to an amplifier for further processing by the receiver module. In the receiver module according to the first aspect of the invention, on both couplers a floating voltage is induced and the difference voltage between the two couplers directly relates to a (low power) electrical field that may be present in the direct vicinity of the body of the user. Thereby the low power electrical field can be better detected. Noise and interference that may be received by the couplers results in a change of the floating voltage of both couplers without significantly changing the difference voltage between the two couplers. Thus, in particular in a body coupled

communication environment, the use of the differential signal between the two couplers as an input for the differential amplifier results in a good suppression of noise and interference received by both couplers.

In addition to the above presented advantage, the receiver module has an architecture which uses at least up to the input of the differential correlator arrangement differential signals. The basis of the differential signals is formed by the two couplers between which a continuously varying differential voltage may be present. Differential signals are formed by a voltage difference between two electrical conductive lines (e.g. two wires, or two metal tracks on an integrated circuit, etc.). Thus, the amplified differential signal is formed as a voltage difference at two output ports of the differential band-pass amplifier and this voltage difference is conducted by two electrical conductive lines to the differential correlator arrangement. As such, noise and interference that is simultaneously received (simultaneously) by both electrical conductive lines is automatically cancelled out - thus, when, for example, the receiver module is implemented on an integrated circuit and the both electrical conductive lines that conduct the differential signal are affected by a signal from the same interference source being present on or being located near the integrated circuit, the differential signal is not affected. The same applies to signal components that are received simultaneously by the two couplers. Consequently, the receiver module according to the invention is well capable of suppressing received noise and interference. Although a single electrical conductor also has a specific difference voltage with respect to the ground voltage, the use of the terms differential signal / differential voltage does not include signals that have a voltage with respect to the ground. The term differential signal is used to distinguish signals transported via a single electrical conductor (which has a voltage with respect to the ground) from signals that are transported as a difference voltage between voltage of two electrical conductors (which are not directly connected to the ground voltage).

In WO2010/049842 a correlator arrangement is discussed which does not receive a differential signal and is not based on the use of differential signals within the correlator arrangement, but which is with respect to other features similar to the correlator arrangement of the receiver module. Thus, advantages and effects of the correlator arrangement which relates to these other features are discussed in patent application

WO2010/049842. The differential correlator arrangement of the invention uses the amplified differential signal as input signal and as such the differential correlator arrangement of the invention has as an additional advantage (compared to the differential correlator arrangement of WO2010/049842) that also within the differential correlator arrangement internal differential signals may be used to prevent the distortion of signals by noise and interference that may be received by both electrical conductive lines that transmit the specific internal differential signal.

The synchronization signal of the differential correlator arrangement is, for example, generated by an internal clock reference of the receiver module (of which, for example, the frequency is controlled as the result of the first correlation) or the

synchronization signal is, for example, a signal that is generated with, for example, a bit- template and an internal clock reference.

The couplers might receive signals from the body transmission channel when the body is in the direct vicinity of the couplers. Direct vicinity means in the context of the invention that the couplers must be within a maximum distance from the body to establish a galvanic or capacitive coupling resulting in the effect that signals may be received and/or transmitted via the body transmission channel. The maximum distance is a defined as a shortest distance between the body of the user and the couplers. Optionally, the maximum distance (of the direct vicinity) is closer than 10 cm, or closer than 5 cm. Optionally, the maximum distance is closer than 2 cm. In an optional embodiment of the invention, direct vicinity means that the user touches the couplers. It is to be noted that, as discussed in the background of the invention section, the couplers are for generating or receiving a low power electrical field and for creating a capacitive or galvanic coupling between the body of the user and the couplers. The couplers may be embodied in electrodes, metal plates, etc.

The differential correlator arrangement comprises a differential clock synchronizer for generating the receiver module timing. The differential clock synchronizer comprises a synchronization loop which uses for at least a part of the internal signals of the synchronization loop differential signals. The receiver module timing is a clock signal or a signal that relates to the clock signal which is used in the receiver module. To be able to decode the signals received by the couplers a clock signal must be present which is synchronized with the frequency of the signal received at the couplers. The differential clock synchronizer comprises a synchronization loop. As such a loop is, for example, discussed in WO2010/049842, and such a loop may be based on phase-locked loop implementations. In the synchronization loops internal signals must be transmitted between different components of the synchronization loop. Often, at least a part of these internal signals of the loop consist of analog signals. The amplified differential signal is also an analog signal an when such a signal, while being processed in the synchronization loop, is kept as long as possible in the form of a differential signal, the differential clock synchronizer provides also effective means to suppress the effects of noise and interference.

Optionally, the differential band-pass amplifier is a low-noise differential band-pass amplifier. Amplifiers may introduce intrinsic noise in the amplified signal. In a low noise amplifier, the input-referred noise, which is the intrinsic noise induced by the low- noise amplifier, integrated in the whole spectral range of interest (the specific spectral range) and referred back to the input, must be lower than the lowest signal that must be amplified by the low noise amplifier or the lowest signal that the system in which the amplifier is used can detect. Thus, the use of the low-noise differential band-pass amplifier also contributes to the suppression of noise and interference. In the following each line where the term differential band-pass amplifier is used, optionally, the term differential low-noise band-pass amplifier may be read, and vice versa.

Optionally, the differential clock synchronizer at least comprises a loop filter which generates a signal for a voltage controlled oscillator. The synchronization loop uses at least up to the loop filter differential signals for its internal signals. Thus, the voltage controlled oscillator controls the frequency of its output signal on basis of a received differential signal. In such a differential clock synchronizer the signals are transmitted as differential signals as long as possible which is advantageous when noise and interference must be suppressed. Optionally, the differential correlator arrangement comprises a differential decoder for decoding / demodulating the amplified differential signal and for generating the received digital signal. The differential decoder comprises at least a comparator for comparing a differential voltage with a predefined voltage to obtain the received digital signal. The differential decoder processes differential signals up to the comparator. Also this optional embodiment of the differential decoder processes the signals as long as possible as a differential signal, and, as such is the influence of noise and interference also effective suppressed in the differential decoder.

Optionally, the differential band-pass amplifier comprises a series arrangement of differential amplifiers. A first differential amplifier of the series arrangement is constituted by a low noise low-pass differential amplifier. The first differential amplifier amplifies differential signals received by the couplers up to an upper frequency, the upper frequency being equal to or larger than the highest frequency of the specific spectral range. A second differential amplifier of the series arrangement is a band-pass differential amplifier. The second differential amplifier amplifies a differential signal with the specific spectral range. It is advantageous to first amplify the differential voltage between the two couplers with a low- noise differential amplifier because it creates the possibility to obtain a first amplification of the signal with a relatively large gain without introducing much noise. Several low-noise differential amplifiers can be used to build a low-pass filter effect with the help of passive R, L, C components or active transconductor circuitry. The low-pass filter effect means that only differential signal up to an upper-frequency are amplified. The upper- frequency may still be relatively high, for example, up to one hundred megahertz. In order to obtain the band-pass filter effect of the differential band-pass amplifier at least one further differential amplifier is required which only amplifies signals in the specific spectral range. The second differential amplifier preferably attenuates signals outside the specific spectral range such that low- frequency signals that may be amplified by the first differential amplifier are effectively suppressed.

Analog filters are often made of operational amplifiers combined with a passive RLC network. A minor adaption of these analog filters results in the creation of an amplifying filter and as such, the sub-components of the series arrangement are known.

A further advantage of the use of the series arrangement is that, when using a low noise amplifier with a relatively large gains as a first stage of the series arrangement, noise requirements of the subsequent stages are less strict and a bias current of the subsequent stages can be effectively reduced. Also, when the overall gain of the series arrangement is controllable, the controlling may start by reducing the gain of the last stage of the series arrangement without affecting the overall noise behavior of the amplifier as a whole.

Optionally, a gain of the differential band-pass amplifier is controllable in dependence of a gain control signal. When the gain is controllable, the optimal amplification factor may be obtained such that the correlator arrangement is capable of generating the receiver module timing and is able to decode the received signals and such that, for example, simultaneously power is saved by preventing a high amplification. Optionally, the gain of the differential band-pass amplifier may be a first gain or a second gain and the differential band- pass amplifier may switch from the first gain to the second gain and vice versa in dependence of the gain control signal. The gain of the differential band-pass amplifier may be

controllable in a plurality of discrete steps, or may be controllable in a continuous range.

Optionally, the differential band-pass amplifier further comprises a signal level detector for generating a signal level signal indicating a level value that is related to the amplitude of the signals received at the couplers. The obtained information by the signal level detector may be used by the receiver module and/or a transceiver module or body coupled communication device in which the receiver module is provided to estimate quality parameters of the communication channel and to optimize the amplification of the signals received at the couplers. The information about the signal level enables optimization between, for example, quality of the decode signal (the received digital signal) and power used by the receiver module.

Optionally, the signal level detector compares a differential voltage of an input signal, of an output signal and of at least one differential signal in between the differential amplifiers of the series arrangement with one or more threshold values to generate the signal level signal.

Optionally, at least one of the differential amplifiers of the series arrangement is configured to amplify a differential signal according to a first gain and according to a second gain and the at least one of the differential amplifiers is configured to change its gain in dependence of a gain control signal. This optional implementation of the differential band- pass amplifier allows optimizations for power use and quality of the received signal. In an embodiment, the amplification factor (gain) of the at least one of the differential amplifiers is controllable in a plurality of gain factors.

Optionally, the differential band-pass amplifier may operate in a first frequency mode and in a second frequency mode in dependency of a mode configuration signal. In the first frequency mode, the differential signals of the two couplers are amplified within a first spectral range, and, in the second frequency mode, the differential signals of the two couplers are amplified within a second spectral range. The first spectral range is different from the second spectral range. It is advantageous to have a receiver module that may operate in different frequency bands because it provides an opportunity to choose the frequency band that is distorted by the lowest amount of noise and/or interference. Furthermore, when the data rate of the received and/or transmitted data is different in different periods of time, the optimal spectral range may be selected to transmit and receive this data and, more in particular, the optimization may relate to power optimization because it may be advantageous to use, when the data rate is relatively low, lower modulation frequencies (and, thus, the lowest spectral range) to save power in the transmitter and/or the receiver.

It is to be noted that the optional embodiment is not limited to two frequency modes only. The differential band-pass amplifier may also be configured to operate in more than two different frequency modes.

Optionally, the differential correlator arrangement is configured to operate in the first frequency mode and in the second frequency mode in dependency of the mode configuration signal. In the first frequency mode, the receiver module timing may be synchronized to a frequency in the first spectral range, and, in the second frequency mode, the receiver module timing may be synchronized to a frequency in the second spectral range. This embodiment enables different frequencies modes of the receiver module as a whole and, therefore provides previously discussed advantages of using different frequency modes. For example, when the differential correlator arrangement comprises the differential clock synchronizer which synchronizes the receiver module timing with the amplified differential signal based on a first correlation between the amplified differential signal and the synchronization signal, the synchronization signal is, for example, generated by a voltage controlled oscillator which may be controlled in a first frequency mode or in a second frequency mode in dependence of the mode configuration signal. When the voltage controlled oscillator is controlled in the specific frequency mode the generated signal is, respectively, in the first spectral range or in the second spectral range, and the generated signal may be slightly varied within the respective spectral range in dependency of a provided voltage. In another embodiment, the signal that is generated by the voltage controlled oscillator is provided to a frequency divider which may be enabled or disables on basis of the mode configuration signal. If the mode configuration signal indicates that the differential correlator arrangement has to operate at a lower frequency, the frequency divider is activated to divide the frequency of the output of the voltage controlled oscillator to a lower frequency.

Optionally, the receiver module further comprises a mode controller for processing interrupts and for generating a mode selection signal to control a mode of operation of sub-circuitries of the receiver module and comprises a wake-up receiver that is coupled to the couplers. The wake-up receiver provides a wake-up interrupt to the controller. The differential band-pass amplifier and/or the differential correlator are configured to operate in a sleep mode and in an operational mode in dependence of a mode selection signal that is received from the controller. The wake-up receiver generates the wake-up interrupt when an energy of the signals received at the couplers in a predefined wake-up spectral range exceeds an energy threshold level. The mode controller is configured to control the differential band-pass amplifier and/or the differential correlator arrangement in the operational mode via the mode selection signal when the wake-up interrupt is received.

This optional embodiment enables power saving in the receiver module. In the sleep mode the differential band-pass amplifier and/or the differential correlator arrangement are not operational and may be switched off. At least, in the sleep mode, the differential band-pass amplifier and the differential correlator arrangement do not use much energy. This saves power. The mode controller may control the differential band-pass amplifier and/or the differential correlator arrangement in the sleep mode when, for a period of time, no data was received via the body transmission channel or no data was transmitted via the body transmission. The embodiment provides means to wake-up the differential band-pass amplifier and/or the differential correlator arrangement when it seems that communication is initiated via the body transmission channel. In particular, if another body coupled device wants to start transmitting information to the receiver module, it must first send signals via the body transmission channel in the wake-up spectral range. Such signals are termed wake- up signals. When the receiver module receives these wake-up signals and the wake-up signals transmit a minimal amount of energy, the receiver module is configured in the operational mode by the mode controller such that data and information may be received from the body transmission channel.

According to a second aspect of the invention, a transceiver module is provided. The transceiver module is for use in a body coupled communication device and is capable of receiving and transmitting signals via the body transmission channel. The transceiver module comprises a least a receiver module according to the first aspect of the invention and a transmitter module. The transmitter module is also coupled to the couplers and the transmitter module generates a differential signal that is provided to the couplers in dependence of a transmittable digital signal. The transmittable digital signal comprises in bits the data that must be transmitted via the body transmission channel in the form of bits. In an embodiment, the transmitter module modulates the transmittable digital signal such that an analog signal is obtained that comprises the transmittable digital signal and the analog differential signal is provided to the couplers. In another embodiment, the transmitter module encodes the transmittable digital signal and the encoded (digital) signal is transformed to a differential signal which is provided to the couplers. By providing a differential signal, the generated signal is doubled in strength compared to a single ended configuration and can only, to a limited degree, be influenced by noise and interference before the signal arrives at the couplers.

Optionally, the transmitter module may also operate in a sleep mode and in an operational mode and the transmitter module may switch between these modes in dependence of a mode selection signal (which is, for example, received from a mode controller of the receiver module, or which is, for example, generated by a controller of the body coupled communication device in which the transceiver module is integrated). In an embodiment, when no data must be transmitted via the body transmission channel, in other words, when no transmittable data signal is available, the transmitter module is controlled into the sleep mode. When data must be transmitted, thus, when data is provided via the transmittable digital signal, the transmitter module might be controlled in the operational mode. In another embodiment, the transceiver is configured to either transmit data via the transmitter module or receive data via the receiver module, and when the transmitter module is in the operational mode, the receiver module is controlled in the sleep mode, and when the receiver module is in the operational mode, the transmitter module is controlled in the sleep mode.

Optionally, the transmitter module may be configured to operate in the first frequency mode and to operate in the second configuration mode in dependence of the mode configuration signal. In the first frequency mode, the transmitter transmits signals via the couplers in the first spectral range and, in the second frequency mode, the transmitter transmits signals via the couplers in the second spectral range. Advantages of using different frequency modes have been discussed previously in the context of the receiver module.

Optionally, the transceiver module further comprises a spreader and a despreader. The spreader receives an input digital signal for transmission and generates the transmittable signal. The transmittable signal has a frequency that is at least twice as high as the frequency of the input digital signal and the spreader spreads the information of one bit of the input digital signal over at least two consecutive bits of the transmittable digital signal. The despreader receives the received digital signal (as provided by the differential correlator arrangement) and generates a digital output signal. The received digital signal has a frequency that is at least twice as high as the frequency of the output digital signal. The despreader uses the information of at least two consecutive bits of the received digital signal to generate one bit of the output digital signal. In other words, the spreader introduces redundancy in the signal that must be transmitted by the transmitter module such that a more reliable transmission may be obtained. The despreader performs the inverse operation.

Spreading and despreading may improve the reliability of the communication between transmitters and receivers. Further, specific spreading codes may be used which allow the best possible decoding and despreading. In optional embodiments, different device in the network use different spreading codes (e.g. orthogonal spreading codes), such as, for example, in code division multiplexed access systems such that the different devices may simultaneously access the body transmission channel.

It is to be noted that the transmittable signal often has a fixed frequency, and, thus that the input digital signal has a frequency that is at least half of the fixed frequency. Thus, the spreading operation leads to a reduction of the maximum achievable data rate, but improves the robustness of the transmission.

Optionally, the spreader and the despreader are configured to operate according to a spreading factor and they adapt the spreading factor to the quality of the body transmission channel. The spreading factor defines how many bits of, respectively, the transmittable digital signal and the received digital signal, represent, respectively, one bit of the input digital signal and the output digital signal. By increasing the spreading factor, more redundancy is introduced, and, as such, more distortions of the transmitted / received signal can be overcome. Thus, as the quality of the body transmission channel seems to be relatively poor, the spreading factor is increased, and vice versa. It is to be noted that the transceiver module has specific means to detect the quality of the body transmission channel, for example, in the form of keeping track of bit error rates, measuring the received signal strength, or measuring signal to noise ratios, etc. The quality of the body transmission channel is, for example, used by a controller of the body coupled communication device (or of the transceiver module) to adapt the spreading factor.

Optionally, the transceiver comprises a controller for controlling an operation of modules and circuitries of the transceiver module. The controller is configured according to for instance one of the following options: i) The controller receives the signal level signal and controls parameters of modules and circuitries of the transceiver module in dependence of the received signal level signal. Such parameters are, for example, the frequency mode, the spreading factor, the gain of the differential low-noise band-pass amplifier, etc. All previously discussed controllable parameters may depend on the signal level signal.

ii) The controller is configured to generate the gain control signal. For example, when the signal level signal indicates that the signal level is relatively low, the gain may be increased to a higher value, and vice versa.

iii) The controller generates the mode control signal to control the frequency mode of the transmitter module, the differential low-noise band-pass amplifier, and the differential correlator arrangement (and its sub-components). When, for example, the amount of data that must be transmitted and/or received is relatively low, a lower frequency is selected. When, for example, it has been detected that in one of the first and second spectral ranges the interference and noise level is relatively high, the other one of the first and second spectral range is selected to transmit and/or receive the data.

iv) The controller comprises the mode controller.

v) The controller is configured to adapt the spreading factor of the spreader and the despreader.

It is to be noted that the controller may receive input from the user (e.g. via a user interface), from an application/program that runs on a processing unit of the device which comprises the transceiver unit, or from an internal self-regulatory mechanism. This input may be used by the controller to perform at least one of the above controlling operational.

According to third aspect of the invention, a method of receiving signals via a body transmission channel in a receiver module of a body coupled communication device is provided. The method comprises the steps of:

a) receiving signals at two couplers of the receiving module,

b) amplifying a differential voltage being present between the two couplers to an amplified differential signal by means of a differential low-noise band-pass amplifier, c) synchronizing a receiver module timing with the amplified differential signal based on a first correlation between the amplified differential signal and a synchronization signal, d) decoding the amplified differential signal to a received digital signal by performing a second correlation between the amplified differential signal and the receiver module timing.

The method according to the third aspect of the invention provides the same benefits as the receiver module and/or the transceiver module according to, respectively, the first and second aspect of the invention and has similar embodiments with similar effects as the corresponding embodiments of the modules.

These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.

It will be appreciated by those skilled in the art that two or more of the above- mentioned options, implementations, and/or aspects of the invention may be combined in any way deemed useful.

Modifications and variations of the modules and/or the method, which correspond to the described modifications and variations of the system, can be carried out by a person skilled in the art on the basis of the present description.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

Fig. 1 schematically shows a body coupled communication system,

Fig. 2 schematically shows an embodiment of a transceiver module according to the invention,

Fig. 3 schematically shows another embodiment of a transceiver module, Fig. 4 schematically shows an embodiment of a differential low-noise bandpass amplifier,

Fig. 5a schematically shows a spreader and despreader arrangement,

Fig. 5b schematically shows an embodiment of a wake-up receiver, and Fig. 6 schematically shows a method of receiving signals via a body transmission channel in a receiver module of a body coupled communication device.

It should be noted that items denoted by the same reference numerals in different Figures have the same structural features and the same functions, or are the same signals. Where the function and/or structure of such an item have been explained, there is no necessity for repeated explanation thereof in the detailed description.

The Figures are purely diagrammatic and not drawn to scale. Particularly for clarity, some dimensions are exaggerated strongly. DETAILED DESCRIPTION OF THE EMBODIMENTS

A first embodiment is shown in Fig. 1. Fig. 1 schematically shows a body coupled communication system 190. Fig. 1 shows a first body coupled communication device 100 and a second body coupled communication device 180. If a user 150 is with his body in the direct vicinity of couplers 102 of the first body coupled communication device 100 and if he is with his body in the direct vicinity of a body coupled communication interface (which, for example, also comprises couplers) of the second communication device 180 information may be transmitted via a body transmission channel 160 which follows a body of the user 150. As discussed previously, the body coupled communication devices 100, 180 generate and receive low power electrical fields and data is communicated by modulating the electrical fields. The direct vicinity is a maximum distance between the user 150 and the couplers 102 such that a galvanic or capacitive coupling can be made.

The couplers 102 are, for example, two electrodes or two metal plates 104 which can be brought in the direct vicinity of the body of the user 150. Each of the couplers 102 may receive signals and, as the effect of received varying low power electrical fields, a varying voltage differences may be detected between the two couplers 102. To each one of the two couplers is connected an electrical conduction line and, consequently, two electrical conduction lines transport a received differential signal 112 which is based on the varying voltage differences between the two couplers 102. The received differential signal is provided to a differential low-noise band-pass amplifier 114 which amplifies the received differential signal 112 to an amplified differential signal 108. The differential low-noise band-pass amplifier 114 amplifies according to an amplification gain G and within a specific spectral range the received differential signals 112 are amplified with the amplification gain G, which means that (for the amplified signals) they formulate (V ₂₀ ut-V _l0 ut) = G (V ₂ i _n - Vn _n ). In an embodiment, signals outside the specific spectral range are attenuated by the differential low-noise band-pass amplifier 114. Further, the differential low-noise band-pass amplifier 114 does not introduce much noise. The low-noise characteristic of the differential low-noise band-pass amplifier 114 may be characterized by the parameter Vn, rms (input referred noise for a certain bandwidth of the band-pass amplifier) and the value of the parameter is smaller than the smallest input signal amplitude that the system can detect. A specific embodiment of such a differential low-noise band-pass amplifier 114 will be discussed later in the description. A skilled person in the field of amplifiers knows how to build differential amplifiers as such and how to amplify signals in the specific spectral range without introducing much noise.

The amplified differential signal 108 is provided to a differential correlator arrangement 115 which is configured to synchronize a receiver module timing 116 with the amplified differential signal 108 based on a first correlation between the amplified differential signal 108 and a synchronization signal and which is configured to decode the amplified differential signal 108 to a received digital signal 120 by performing a second correlation between the amplified differential signal 108 and the receiver module timing 116. The differential correlator arrangement 115 may comprise a differential clock synchronizer 118 for generating the receiver module timing 116. The differential correlator arrangement 115 may comprise a differential decoder for demodulating the amplified differential signal 108. It is to be noted that the receiver module timing 116 may also be used to generate a reference signal (e.g. using applying a 1 -bit-template to generate the reference signal - see e.g. WO2010/049842) and that differential correlator arrangement 115 may be configured to decode the amplified differential signal 108 to a received digital signal 108 by performing a third correlation between the amplified differential signal 108 and the reference signal.

Fig. 2 schematically shows an embodiment of a transceiver module 200 for use in a body coupled communication device, such as, for example, the first body coupled communication device 100 of Fig. 1. The transceiver module 200 is for receiving signals from and for transmitting signals via a body transmission channel, such as the body transmission channel 160 of Fig. 1. The transceiver module 200 comprises a transmitter module 202, a spreader 206, a controller 210, a receiver module 106 and a despreader 216. It is to be noted that the controller 210 is drawn without specific connections / couplings to other modules. Other connections / coupling are not drawn to prevent that Fig. 2 becomes an unclear figure. In practical embodiments of the transceiver module 200, the controller 210 receives signals from and provides signals to almost all components of the transceiver module 200 to receive operational information and to control the operation of the

components of the transceiver module 200.

At the left end of the transceiver module 200 are drawn the couplers 102. The couplers 102 are coupled to the transmitter module 202, to a differential low-noise band-pass amplifier 114 and to wake-up receiver 220.

The transmitter module 202 receives a transmittable signal 204 which comprises data that must be transmitted through the body transmission channel. The transmitter module 202 generates an analog differential signal (which comprises digital information) which is provided to the couplers based on the transmittable digital signal 204. The transmitter module 202 modulates or encodes, for example, the transmittable digital signal 204 at a specific frequency. The transmittable digital signal 204 may be received from other circuitries of the body coupled communication device, but may also be provided by a spreader 206 which spreads the bits that must be transmitted via the body transmission channel over a plurality of bits in the transmittable signal.

The spreader 206 receives an input digital signal 208 from applications and circuitries of the body coupled communication device and each bit is spread over two or more bits in the transmittable digital signal 204 according to a spreading code. A typical parameter of a spreader 206 is the spreading factor which is defined as the number of bits in the transmittable digital signal 204 that correspond to one bit in the input digital signal 208. The spreading factor, may, for example, be controlled by the controller 210.

It is further to be noted that the transmitter module 202 may operate in a first frequency mode and in a second frequency mode. In the first frequency mode the generated differential signal is in a first spectral range and, in the second frequency mode, the generated differential signal is in a second spectral range. The specific modulation technique used in the transmitter module 202 determines how the different differential signals of the two frequency modes are generated. In a specific embodiment, the transmitter module 202 comprises an internal clock that is controlled to a different frequency when the transmitter module 202 is controlled in a different frequency mode. In an alternative embodiment, the transmitter module comprises two sub-modules which operate at different frequencies, and, in the first frequency mode, only the first sub-module is used and, in the second frequency mode, only the second sub-module is used. The transmitter module 202 switches between frequency modes in dependency of a mode configuration signal that is, for example, generated by the controller 210.

The transmitter module 202 may also be controlled in a sleep mode in which it uses almost no power and in which it is not able to generate a differential signal for the couplers 102. The transmitter module 202 may also be controlled in an operational mode in which it is capable to perform all of its functions. The controller 210 may provide a mode selections signal to the transmitter module 202 to control the transmitter module either in the sleep mode or in the operational mode.

The receiver module 106 provides the received digital signal 120. This signal is provided to a despreader 216 which generates an output digital signal 218. The function of the despreader 216 is the reverse of the function of the spreader 206. Two or more bits of the received digital signal 120 are mapped on one bit of the output digital signal 218 in dependency of a spreading code that was used by the transmitter of the received signals.

As discussed previously, the receiver module 106 comprises the couplers 102, the differential low-noise band-pass amplifier 114, the differential demodulator 110 and the differential clock synchronizer 118. The differential low-noise band-pass amplifier 114, the differential decoder 110 and the differential clock synchronizer 118 may be controlled in a sleep mode and in an operational mode. In the sleep mode they do not use much power and they cannot perform their function. In the operational mode they are fully capable to perform their function. They may be controlled in the operational mode and the sleep mode by a mode configuration signal 226. The mode configuration signal may be generated by the controller 210 or by a dedicated mode controller 224. The receiver module 106 may comprise a wake- up receiver 220 which also receives the differential signals 112 from the couplers 102. When an energy of the signals received by the couplers in a predefined wake-up spectral range exceeds an energy threshold level, the wake-up receiver generates a wake-up interrupt 222. The wake-up interrupt 222 is provided to the mode controller 224 and the mode controller 224 generates the required mode configuration signal 226 to control components of the receiver module 106 in the operational mode. The mode controller 224 may also be a specific sub-component of the controller 210. The wake-up receiver 220 is designed to use a relatively low amount of energy such that, when the transceiver module 200 does not receive and does not transmit signals via the body transmission channel and most components of the transceiver module 200 are controlled in the sleep mode, the transceiver module 200 as a whole uses a very low amount of energy.

The differential low-noise band-pass amplifier 114 may comprise a signal level detector 212 which generates a signal level signal that indicates with a value how low or high the amplitude of the signals received at the couplers 102 is. The signal level signal may be provided to the controller 210 such that the controller 210 is capable of controlling other parameters of the transceiver module in dependence of the received signal level. In particular, the signal level signal allows the controller 210 to control the transceiver module 200 at an optimal operational point at which the transceiver module receives and transmits data without the generation of many bit errors, while the power used by the transceiver module 200 is minimized.

The differential low-noise band-pass amplifier 114 may also operate in the first frequency mode and in the second frequency mode in dependency of a mode

configuration signal that it receives from the controller 210. The differential low-noise band- pass amplifier 114 amplifies signals in a specific spectral range, and in the first frequency mode, this is within the first spectral range and in the second frequency mode, this is in the second spectral range. In dependency of the mode configuration signal, specific components of the differential low-noise band-pass amplifier 114 are switched off or switched on to obtain another frequency response. For example, capacitors, inductances, resistors or current sources are activated or de-activated to influence the frequency response of the differential low-noise band-pass amplifier 114.

The differential decoder 110 receives a receiver timing signal 116 which relates to the frequency of the signals received at the couplers 102. The differential decoder 110 uses this signal to accurately decode each bit of the amplified differential signal 108. The differential decoder 110 at least comprises a differential comparator 214 which compares a voltage difference between two electrical conductive lines with one or more threshold values to generate the received digital signal. This architecture of the differential decoder 110 is such that the processed amplified differential signal is kept as a differential signal up to the differential comparator 214.

The differential clock synchronizer 118 generates the receiver module timing 116 which is based on the frequency of the amplified differential signal 108. This is done by a synchronization loop 228. The synchronization loop 228 is at least partially based on differential signal 230. For example, a phase-locked loop implementation may be used to generate the receiver module timing 116 and at least one of the components of the phase- locked loop has an output signal which is a differential signal. In an embodiment, the synchronization loop 228 comprises a loop filter which generates a voltage for a voltage controlled oscillator and the synchronization loop is at least based on differential signals up to the loop filter. The differential clock synchronizer 118 may also operate in the first frequency mode and in the second frequency mode in dependency of a mode configuration signal that it receives from the controller 210. In the first frequency mode, the differential clock synchronizer 118 is capable of generating the receiver module timing on basis of the amplified differential signal 108 that is within the first spectral range, and in the second frequency mode, the differential clock synchronizer 118 is capable of generating the receiver module timing on basis of the amplified differential signal 108 that is within the second spectral range.

Fig. 3 schematically shows another embodiment of a transceiver module 300. The architecture of the transceiver module 300 is similar to the architecture of the transceiver module of Fig. 9 of WO2010/049842. The transceiver module 300 comprises two couplers 102, a transmitter module 202, a spreader 206, a despreader 216, a differential decoder 110, a differential clock synchronizer 118, a wake-up receiver 220 and a controller 210. In particular the architecture and functions of the modules of the differential decoder 110 and of the differential clock synchronizer as such 118 are extensively discussed in WO2010/049842 and reference is made to this document for those details. It is seen in Fig. 3, that the differential decoder 110 has a differential comparator 214 and that all signals transmitted within the differential decoder 110 are differential signals up to the differential comparator 214. Fig. 3 shows that the differential clock synchronizer 118 is based on differential signals up to the loop filter 319. A skilled person in the art of electronics knows how to change a non-differential implementation of components of the differential decoder 110 and of the differential clock synchronizer 118 towards a differential implementation.

The example of the transmitter module 202 comprises a Manchester encoder to encode the transmittable digital signal (in Fig. 3 "TX chips", 390) to a specific frequency. The output of the Manchester encoder is still a digital signal. The digital signal is buffered and converted towards a differential digital signal that is provided to the couplers 102. The example of the wake-up receiver 220 is discussed later on.

Fig. 4 schematically shows an embodiment of a differential low-noise bandpass amplifier 400. The differential low-noise band-pass amplifier 400 comprises a series arrangement of differential amplifiers 412, 414, 416, 418, 422 to generate the amplified differential signal 108. Two differential amplifiers 412, 422 have, in additional to being an amplifier, a low-pass filter character, which means that signals below a particular frequency are amplified and signal with a frequency above that particular frequency are attenuated. The last differential amplifier 422 does not necessary amplify the voltage level of the differential signal, but may act as a buffer amplifier. The other differential amplifiers 414, 416, 418 of the series arrangement have, besides the function of an amplifier, also the function of a bandpass filter. At least one of the other differential amplifiers 414, 416, 418 has such a band-pass characteristic in the specific spectral range such that the differential low-noise amplifier 400 amplifies signals within the specific spectral range and attenuate signals outside this spectral range. Preferably the first differential amplifier 412 of the series arrangement has a relatively high amplification factor ("gain") and at least the first differential amplifier 412 is a low- noise amplifier, which means that both the introduction of noise by this differential amplifier 412 is minimized and the impact of noise introduced in subsequent stages of the series arrangement is minimized. The differential low-noise band-pass amplifier 400 also comprises a signal level detector comprising an additional differential amplifier 420, three 1-bit level detectors 406, 408, 410 and a thermometer-to-binary converter 404.The presented signal level detector is just an example and other signal level detectors may be used as well. The presented signal level detector is integrated with the series arrangement of differential amplifiers 412, 414, 416, 418 and measures at specific points in between two differential amplifiers whether the signal level (e.g. amplitude) exceeds a threshold value - the comparison with threshold value(s) is performed by the 1-bit level detectors 406, 408, 410. If the differential voltage at the input of the 1-bit level detectors 406, 408, 410 exceeds the threshold value, the value of an output bit of the 1-bit level detector 406, 408, 410 is set to another value (e.g. from 1 to 0 or vice versa). If a sequence is formed by the output bits of the 1-bit level detectors 406, 408, 410 a so-termed thermometer code is obtained. In this code, if the encoded value increases, more bits (seen from one side to another side of the sequence) are set to a specific value. For example, when the 1-bit level detectors 406, 408, 410 of Fig. 4 change their output values from 0 to 1 when the amplitude of the differential voltage is above the threshold level, the possible sequences of bits are, presented in the order of an increasing signal level, 000, 001, 011 and 111. The thermometer-to-binary converter 404 converts the thermometer coding of the outputs of the 1-bit level detectors 406, 408, 410 towards a (2-bit) binary encoding.

Finally, the signal level detector provides a binary signal level signal 402 which indicates with a binary value an amplitude level of the differential signal 112 received at the couplers.

The example of Fig. 4 presents a series arrangement of differential amplifiers 412, 414, 416, 418, 422 with five differential amplifiers. However, it is to be noted that in other implementations less differential amplifiers may be used. For example, instead of the differential amplifiers 412, 414, a single differential amplifier 424 may be used and instead of the differential amplifiers 416, 418, a single differential amplifier 426 may be present in the low-noise band-pass differential amplifier 400.

It is to be noted that at least the first differential amplifier 412, and possible also other differential amplifiers 414, 416, 418, 420, 422 are configured to operate in at least a first amplification mode and in a second amplification mode, wherein, in each one of the amplification modes the gain (amplification factor) has another value. The differential low- noise band-pass amplifier 400 may receive a gain control signal (not shown) which is used to control the differential amplifiers 414, 416, 418, 420, 422 in a specific amplification mode. The signal level signal 402 is provided to a controller which may decide to adapt the overall gain of the differential low-noise band-pass amplifier 400 by providing a specific gain control signal. By using such a control loop, the amplitude of the amplified differential signal 108 may be optimized with respect to a maximum allowable amplitude for the amplified differential signal.

In an embodiment of the differential low-noise band-pass amplifier 400, the differential amplifiers 412..422 are configured to operate in a first frequency mode and to operate in a second frequency mode in dependency of a mode configuration signal (not shown). In the first frequency mode signals in a first spectral range are amplified and in the second spectral range signals in the second spectral range are amplified. It has been previously discussed how such different frequency modes may be obtained in the differential amplifiers 412..422. In an alternative embodiment of the differential low-noise band-pass amplifier 400, two parallel series arrangements of differential amplifiers are implemented and in each one of the frequency modes only one series arrangement is switched on, while the other one is switched off, and each one of the two series arrangements of differential amplifiers is optimized to operate in a specific spectral range.

In an embodiment, as discussed previously, the differential low-noise bandpass amplifier 400 may be controlled in a sleep mode and in an operational mode in dependence of a mode selection signal (not shown). In the sleep mode, for example, all elements of the differential low-noise band-pass amplifier 400 are switched off and, in the operational mode, all elements are switched on.

Fig. 5a schematically shows a spreader and despreader arrangement 500. The arrangement 500 the transmittable digital signal 204 by multiplying (XOR) the bit fetched from the transmit buffer with a spreading code from the code sequencer. The de-spreading function is the reverse process in which the received digital signal 120 is multiplied with the spreading code sequence, averaged (integrator) and thresholded (decision) to construct the output digital signal 218. While the timer unit takes care of controlling the (de-)spreading factor, the synchronizer unit handles the task of aligning the local code generation with the incoming chips for proper de-spreading. The arrangement 500 receives a clock signal 504 form another component of the transceiver module, for example, from the differential clock synchronizer. The arrangement 500 generates a spreading code signal 502 which might be used by other components of the transceiver module. A chip-error-rate (CER) information (e.g. derived during a preamble interval of transmitted data packets) may be used by the controller to estimate the channel quality. Subsequently, this information may be used to determine the spreading factor (SF), symbol decision threshold and possibly the spreading code type to improve the robustness of the communication link. The receiving and transmitting devices may exchange channel quality information during link set-up and decide the parameter settings that reduce the bit error rate while keeping the link power consumption low.

Fig. 5b schematically shows an embodiment of a wake-up receiver 550. The wake-up receiver receives a differential signal 112 from the couplers and generates a wake- up interrupt 566. The wake-up receiver 550 comprises a series arrangement of a differential amplifier 552, a differential band-pass filter 556, a differential signal level integrator 560 and a differential comparator 564. The differential amplifier 552 amplifies the differential signal 112 of the couplers towards a differential signal 554 which is provided to the differential band-pass filter 556. The differential band-pass filter 556 only allows a passage of signals in a wake-up spectral range. The wake-up spectral range is a range in which a transmitter transmits signals to wake-up a receiver module / device. The differential band-pass filter 556 generates a filtered differential signal 558 which is provided to the differential signal level integrator 560 which integrates the received energy of the filtered differential signal 558 over a specific period of time. The specific period of time may have a predefined length, or the length of the specific period of time is controlled by, for example, the controller 210 of the transceiver module 200 of Fig. 2. The output of the differential signal level integrator 560 is an integrated differential signal 562 which is provided to a differential comparator 564. The differential comparator 564 compares a voltage level between the two electrical conductors that conduct the integrated differential signal 562 with an energy threshold value. If the integrated differential signal 562 indicates a value that is larger than the energy threshold value, a wake-up interrupt 566 is generated. The energy threshold level may be a predefined threshold level or may be controlled by, for example, the controller 210 of the transceiver module 200 of Fig. 2. It is to be noted that some of the sub-modules of the wake-up receiver 500 may also be combined in a single block, such as, for example, the differential amplifier 552 and the band-pass filter 556 may be embodied in a single band-pass differential amplifier.

Fig. 6 schematically shows a method 600 of receiving signals via a body transmission channel in a receiver module of a body coupled communication device. The method comprises the stages of: i) receiving 602 signals at two couplers of the receiving module, ii) amplifying 604 a differential voltage being present between the two couplers to an amplified differential signal by means of a differential low-noise band-pass amplifier, iii) synchronizing 606 a receiver module timing with the amplified differential signal based on a first correlation between the amplified differential signal and a synchronization signal, and iv) decoding 608 the amplified differential signal to a received digital signal by performing a second correlation between the amplified differential signal and the receiver module timing.

In summary, the present application provides a receiver module, a transceiver module and a method of receiving signals via a body transmission channel in a receiver module. The receiver module comprises two couplers for receiving signals from the body transmission channel. A differential signal obtained by the couplers is provided to a differential low-noise band-pass amplifier to amplify the received signals in a specific spectral range towards an amplified differential signal. The amplified differential signal is provided to a differential correlator arrangement which synchronizes a receiver module timing with the amplified differential signal and to decode the amplified differential signal. The architecture of the receiver module is based on amplifying and processing differential signals. Thereby the receiver module is better capable of suppressing noise and interference signals.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims.

In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.