WO2021075961A1

WO2021075961A1 - A low-power system, transmitter, receiver for signal acquisition and transmission

Info

Publication number: WO2021075961A1
Application number: PCT/NL2020/050632
Authority: WO
Inventors: Ömer Can AKGÜN; Alberto Gancedo REGUILON; Wouter Anton SERDIJN
Original assignee: Technische Universiteit Delft
Priority date: 2019-10-14
Filing date: 2020-10-14
Publication date: 2021-04-22
Also published as: NL2024016B1

Abstract

The present invention relates to a low-power signal acquisition system for remote biosensing comprising: a converter unit, comprising ATCs connected in cascade as a chain for sampling and converting an input signal into an output signal of pulses with varying pulse-widths; a communication unit; and a control unit, arranged for receiving said output signal and control of said communication unit to transmit said output signal; wherein said communication module comprises a pulse harmonic modulation unit for driving said coupling link with a sharp impulse generating an oscillation pulse with rapid rise and slow decay, and generate a further oscillation pulse with predetermined delay for suppression of said oscillation pulse for forming a bitstream between said oscillation pulse and said further oscillation pulse to transmit said digital signal to said remote receiver; wherein said pulse harmonic modulation unit further comprises a damping switch a drive switch and an impulse generator.

Description

Title: A low-power system, transmitter, receiver for signal acquisition and transmission. Description

The present invention relates generally to a low-power system, transmitter, receiver for signal acquisition for remote biosensing.

BACKGROUND OF THE INVENTION

Implantable devices are a type of medical implants which consist of electronics and suitable for partly but mostly total introduction in the human body with the intention to remain there for a certain period of time and at least beyond the procedure of implanting the device. Implantable devices may be classified as active and/or passive device of which the active devices contain electronics which are powered by some power source.

One of the major challenges in active implantable devices is the search for extremely low-energy signal acquisition systems which can drastically lower battery use and thus increase battery life. As a result, smaller batteries may be used. Since batteries are often one of the components of implantable devices which have a large impact on the dimensions, lower battery usage, and thus smaller batteries, will result in smaller devices.

Wireless transmission has emerged as a popular and essential feature of the active implantable devices in order to transfer the data and possibly also power to and from the device. Communication with a coupling link is one of the most popular and effective means for realizing the communication of data and/or power to and from the device. Since the communication of the data and the power is one of the most power consuming elements of the device, the goal to lower battery usage is most likely to be achieved through improvements in the communication chain.

Conventional methods for lowering power consumption of the wireless transmission typically result in shorter transmission paths/ranges and lower throughput. There is however a limit to lowering throughput since some applications require high bandwidth, and decreasing the transmission path will also limit the devices’ applications. In view of the above, there is a need for an improved system of signal acquisition for remote biosensing with reduced power consumption.

SUMMARY

It is an object of the present invention, to provide an improved system and method of signal acquisition for remote biosensing with reduced power consumption.

In a first aspect, there is provided, a low-power signal acquisition system for remote biosensing, said system comprising: a converter unit, comprising a plurality of analog-to-time converters, ATCs, said ATCs being connected in cascade as a chain of ATCs, wherein said chain of ATCs is arranged for sampling and converting an input signal such as an input signal obtained from an electrode in, or on a biological tissue and wherein the voltage of the input signal is converted into an output signal of pulses with varying pulse-widths; a communication unit, arranged for communication over a short range coupling link, wherein the output signal is modulated by a modulation scheme for wireless transmission over said coupling link to a remote receiver unit for further processing of said output signal; a control unit, arranged for receiving said output signal from said chain of ATCs and for control of said communication unit to transmit said output signal; wherein said communication module comprises a pulse harmonic modulation unit arranged for driving said coupling link with a sharp impulse for generating an oscillation pulse with a rapid rise and slow decay, and wherein said unit is further arranged to generate a further oscillation pulse with a predetermined delay for suppression of said oscillation pulse for forming a bitstream between said oscillation pulse and said further oscillation pulse to transmit said digital signal to said remote receiver; and wherein said pulse harmonic modulation unit further comprises a damping switch a drive switch and an impulse generator, wherein said impulse generator is connected to the input of said pulse harmonic modulation unit for generating said narrow pulse on the basis of said input for driving said drive switch to generate said oscillation pulse, and wherein said damping switch is connected to the input of said pulse harmonic modulation unit for triggering said further oscillation pulse with said predetermined delay for suppression of said oscillation pulse; and wherein said chain of ATC’s is arranged for generating said output signal wherein the input voltage of said input signal of said electrode is modulated by a varying pulse-width of said pulses of said output signal.

In signal acquisition systems for remote biosensing there is a tendency towards lowering the supply voltage to achieve a lower power consumption and safe battery life. Lower power consumption and longer battery life enables the use of smaller batteries which is one of the key challenges in the design of active implantable medical devices.

Lowering the supply voltage will reduce the voltage headroom for the transistors to operate in saturation. Without operating in the saturation it is very hard to realize signal processing and amplification function in the analog domain. Time mode signal processing may solve these issues since the time-mode operation modulates the information in the time difference between two subsequent switching events. The modulation expresses an N bit signal.

By lowering the number of switching events, the power consumption may be lowered. As such, by use of time-mode signal processing, the device benefits from the lower power consumption such that smaller batteries may be used.

Time-mode signal processing has a relative low throughput, however, for applications in which no high throughput is required, this is not a drawback.

In a first aspect of the low-power signal acquisition system for remote biosensing a converter unit is presented. The system comprises at least three main components, a converter unit, a communication unit and a control unit. The converter is connected to the electrode and the communication comprises a coupling link which may be an inductive or a magnetic coupling link to communicate the data towards a remote receiver, which in case of an implantable medical device, is outside the biological body.

The converter consists of a plurality of analog-to-time converters, also referred to as ATCs. These ATCs are connected in series to form a chain of converters. The ATCs of the chain are connected to the electrode and thus arranged to obtain an input signal from the electrode which may either be placed inside or outside the body of a mammal. The ATC converts an input voltage at the electrode to an output signal preferably with a fixed output voltage or amplitude. Alternatively, in all examples of the disclosure, the input voltage may also be an input current. The information obtained or sampled at the electrode is modulated into the output signal by variation of the pulse-width.

The ATCs comprise multivibrators. Multivibrators in general are used to implement a two-state device such as a flip-flop. It consists of two amplifiers which are cross coupled by resistors or capacitors. The ATCs of the system according to the first aspect comprises monostable multivibrators, which preferably have tunable pulse- widths, which are circuits in which one of the states is stable, but the other state is unstable or transient for a tunable period. The monostable multivibrators generate output pulses. When they are triggered, a pulse of a variable and tunable duration is generated. The output state, e.g. high, is kept stable for the mentioned variable and tunable duration, independent of the input state of the ATC. Once the variable duration has lapsed, a next pulse of a varying duration may be generated upon the next trigger.

The ATC is thus particularly useful for generating single output pulse of adjustable time duration in response to a triggering signal. The ATCs of the first aspect modulate the input signal by a pulse-width variation.

The signal, once converted by the ATCs is communicated to a remote receiver unit for further processing. The communication is performed by a communication unit of the system which transmits the output signal over a short-range inductive or magnetic coupling link. The coupling link consists of a transmitter and a receiver which use a modulation scheme based on single-pulse harmonic modulation. To this end, the communication unit comprises a pulse harmonic modulation unit. The pulse harmonic modulation unit is arranged to drive the coupling link to transmit the output signal with a narrow or sharp impulse. The sharp impulse will generate an oscillation pulse with an approximately similar rise and decay times. The communication unit is further arranged to generate a second or further oscillation pulse. The second or further oscillation pulse has a predetermined delay in respect of the (first) oscillation pulse and suppresses this (first) oscillation pulse. In time frame generated between the oscillation pulse and the suppression thereof by the second or further oscillation pulse will form a bitstream in which the output signal, i.e. the input signal which is modulated by a variation in pulse-width by the ATCs can be transmitted to the remote receiver over the coupling link.

The communication unit further also comprises a damping switch, a drive switch as well as an impulse generator. The impulse generator is connected to the input of said pulse harmonic modulation unit and generates a narrow pulse on the basis of the input which drives the drive switch, which in turn will generate the oscillation pulse. The damping switch is connected to the input of the pulse harmonic modulation unit and triggers the further oscillation pulse with the predetermined delay for suppression of the oscillation pulse.

As a result, the communication unit will generate a pulse, to mark either the beginning or ending of the transmitted data, effectively increasing the throughput. The width of the damping pulse is less critical, which allows a complete damping of the oscillating signal between the two transmissions per sample.

With the communication module according to the first aspect of the disclosure use is made of a single-pulse harmonic modulation which inherently makes use of the time-mode signals from the ATC chain. The inventor found out that this resulted in an extremely low power consumption. Moreover, the communication module can be implemented in a simplistic manner making the communication module less complex, lower in power consumption and more robust. By employing time-mode signal processing throughout all components of the system, both the converter unit and the communication unit are based on time-mode signal processing, the power efficiency of the system is dramatically improved as compared to conventional signal acquisition and transmission systems for remote biosensing.

As indicated, what is disclosed is particularly suitable for remote biosensing. However, the skilled person will appreciate that this is merely an example for the signal sensing and transmission system, and that the disclosure, according to any aspect or example, may be useful and applicable for other applications of signal sensing and transmission as well. In an example, the converter unit comprises a chain of ATCs which are arranged to generate a pulse independent from the input signal of the electrode.

In an example, the converter unit is arranged to generate a trigger signal in between each of said ATCs.

In an example, the trigger signal in between each of said ATCs uses a fixed-width pulse generator which is activated by the falling edge of the ATC output pulse.

In an example, the system further comprises an interface unit arranged between said converter unit and said communication unit which is arranged to trigger signal from the chain of ATCs is captured by use of a positive-edge triggered flip-flop and wherein the end of the summation of the output signal of the chain of ATCs is captured by use of a negative-edge triggered flip-flop, for generating a start and finish marker of the conversion of the input signal.

In an example, the payload of the output signal being transmitted is comprised solely from the alternating start and finish markers of the conversion of the input signal of the converter unit.

In an example, the system further comprises two either-edge pulse generators for generating control signals to control the driving switch for driving said coupling link.

In an example, the pulse-width of the ATCs are configurable for compensation of variation in the conversion of said input signal.

In an example, the converter unit is comprised of a chain of at least 1 ATC, and preferably, between 2 and 1024 ATCs, more preferably between 4 and 512 ATCs, even more preferably in between 8 and 256 ATCs. These are examples. The ATCs used are at least 1 , and may be up to an unlimited number of ATCs. In a more practical embodiment, 2, 4, 6, 8, 16, 32, 64, 128, 256, 512 or 1024 ATCs may be used. In an example, each of said ATCs is comprised of a single PMOS transistor for tunability and variation of the generated pulse-widths, a NOR logic gate and logic inverters.

In an example, each of the transistors of the chain of ATCs operate in near threshold region. The ATCs can work in any regime from subthreshold to above-threshold, but in an example they work subthreshold, near threshold, or above threshold, of which the near threshold is preferred.

In an example, the system is comprised in a wearable system based on electrical biosignals and preferably comprising an active electrodes for obtaining said input signal.

The system may be comprised in a system which registers electrical biosignals, or bioelectrical time signals. Such a signal refers to the change in electric current produced by the sum of an electrical potential difference across a specialized tissue, organ or cell system like the nervous system. The system may comprise any one of the group of electroencephalogram (EEG), electrocardiogram (ECG), electromyogram (EMG).

In a second aspect there is provided a bio-implantable device, comprising a signal acquisition and transmission system according to any of the previous claims descriptions.

In a third aspect there is provided a transmission module for a low- power signal acquisition system for remote biosensing according to any of the previous descriptions, comprising a communication unit, arranged for communication over a short range coupling link, wherein the output signal is modulated by a modulation scheme for wireless transmission over said coupling link to a remote receiver unit for further processing of said output signal; wherein said communication unit comprises a pulse harmonic modulation unit arranged for driving said coupling link with a sharp impulse for generating an oscillation pulse with a rapid rise and slow decay, and arranged to generate a further oscillation pulse with a predetermined delay for suppression of said oscillation pulse for forming a bitstream between said oscillation pulse and said further oscillation pulse to transmit said digital signal to said remote receiver; and wherein said pulse harmonic modulation unit further comprises a damping switch a drive switch and an impulse generator, wherein said impulse generator is connected to the input of said pulse harmonic modulation unit for generating said narrow pulse on the basis of said input for driving said drive switch to generate said oscillation pulse, and wherein said damping switch is connected to the input of said pulse harmonic modulation unit for triggering said further oscillation pulse with said predetermined delay for suppression of said oscillation pulse.

In a fourth aspect there is provided a receiver module for a low-power signal acquisition system for remote biosensing according to any of the previous descriptions wherein said receiver module comprising a communication unit, arranged for communication over a short range inductive coupling link, arranged to communicate with a transmission module according to the previous description.

In all aspects of the disclosure, an energy harvesting module may be introduced for powering the components of the system through energy harvested from several sources. For example, it may comprise an energy harvesting module arranged for, or be arranged to perform a step of harvesting energy from one or more of the group comprising solar power, thermal energy, wind energy, salinity gradients, and kinetic energy (also known as ambient energy), Alternatively, or additionally, energy may also be harvested through the oxidation of blood sugars, e.g. by comprising one or more biobatteries. These can be used for example to power the biosensor when implanted. The energy harvesting module may be provided as connectable a stand alone module, but is preferably integrated into the biosensor chip or on the biosensor system. The energy harvesting module is preferably arranged to harvest sufficient energy for powering a the biosensor system according to the disclosure which consumes approximately less than 100 nanowatt, more preferably less than 25 nanowatt, even more preferably between 1 and 20 nanowatt and most preferably between 10 and 20 nanowatt.

Although throughout the disclosure reference is made to the low- power signal acquisition system for remote biosensing as an (bio)implantable medical device, the proposed biosensor is, in all aspects of the present disclosure, arranged both for use as an implantable device but also as a biosensor which is located outside of the body of the mammal, and wherein the sensor is connected and connectable to electrodes inside the body for performing the sensing. Hence, in such a embodiment, the electrodes are implantable, or at least partly implantable, but the processing is performed outside the body in the chip.

The invention will hereinafter be further clarified with reference to the drawing of exemplary embodiments of a system according to the disclosure that is not limiting as to the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawing: figure 1 shows the system according to an aspect of the present disclosure; figure 2 shows the converter unit according to an aspect of the present disclosure; figure 3a and 3b show an oversampling chain and trigger generating unit according to an aspect of the present disclosure; figure 4 shows an interface between the converter unit and the communication unit according to an aspect of the present disclosure; figure 5 shows the transmitter and the receiver according to an aspect of the present disclosure; figure 6 shows a signal response of the system according to an aspect of the present disclosure.

Whenever in the figures the same reference numerals are applied, these numerals refer to the same parts.

DETAILED DESCRIPTION

Fig. 1 shows an embodiment 100 of the low-power signal acquisition system according to the present description. The embodiment is particularly suitable for signal acquisition and transmission for biosensors, however, the skilled person will appreciate that the system may also be used for other low power applications in which signals for example from an electrode may be sensed and transmitted to a receiver. The system 100 shown in fig. 1 is comprised of several components, the electrode 104 is on the input side and is the component that will for example be placed in the tissue of a mammal in order to record biosignals. The electrode 104 is connected to a low-power signal acquisition system 103. The low-power signal acquisition system 103 is connected to a receiver 102 which may for example be located on the surface of the mammal or in a remote location, which in particular may be defined as a range between a few centimetres to a few meters. The receiver 102 communicates with the communication module in the system 103, which may be located under the tissue of the mammal, through an inductive link 101. The inductive link may however also be a magnetic link or any other electromagnetic communication link.

An example of a suitable application for a low-power signal acquisition system 100 is the use in EEG, ECG or EMG, or at least a system which registers electrical biosignals. Such ensing systems sensors require low power consumption and have noise constraints.

The low-power signal acquisition system 100 of fig. 1 comprises at least three main components; a converter unit (ATC chain), a control unit (Comm. Control) and a communication unit (transmitter).

The converter is formed by a chain of analog-to-time converters connected in series. These ATCs receive the input signal or biosignal from the electrode 104. The control unit interfaces the ATC chain with the transmitter and the communication unit drives the inductive link 101 to use a single-pulse harmonic modulation scheme to transmit the data obtained from the electrode 104.

The ATC chain converts the input voltage or current at the electrode to an output pulse or output signal, of which the pulse width is modulated by the electrode’s signal voltage. The output of the ATC chain and the trigger signal are then fed to the control unit to create the control signals for the communication module. When the signal is transmitted through the inductive link, the receiver circuit generates two events per conversion (one for the rising edge and one for the falling edge of the converter’s total output pulse) that represent a sampled EEG value. The time between those pulses can be converted into digital by directly interfacing the receiver to an asynchronous TDC.

Fig. 2 shows the converter unit as shown as ATC chain in Fig. 1. The converter unit uses a monostable multivibrator to convert the signal voltage or current from the electrode to a time-mode signal by modulating the current generated by pMOS transistor M1 in a similar fashion. The operation of the circuit is as follows: At the instance that a trigger pulse is applied, Node n1 is pulled low by the NOR gate followed by Node n2, and the current supplied by M1 starts to charge n2. Once n2 is charged to the threshold voltage of the inverter, Node n1 goes low again, making the output high and successfully creating a pulse, that represents the sampled and converted value. The system remains in steady state (Nodes n1 and n2 are logic high) until the next trigger pulse arrives. As the current supplied by Transistor M1 is modulated by the input signal, the output pulse-width will be proportional to the input signal’s amplitude.

The communication module has an inherent time- out feature and will always generate a pulse event at Node n1 , regardless of the input signal value at Vin, avoiding stalling of the chain.

Due to the extremely low amplitude of the signals coming from the input electrode, oversampling and/or sharp filtering are preferred to reduce the noise levels. Due to the oversampling all sources of error and/or noise appear with a Gaussian distribution on top of the signal, which preferably will be reduced in power by a factor of 2, i.e. 3dB, per doubling of the oversampling ratio (OSR) while keeping the signal power constant.

Fig. 3a shows an example of an oversampling chain of ATCs. Addition of the time pulses is performed by chaining ATCs (301a, 300b,... , 300n) and creating a trigger signal between the ATCs using a fixed- width pulse generator as shown in Fig. 3b that activates with the falling edge of the ATC output pulse. With the addition operation of the same converted signal in the time domain (oversampling), the noise contribution is significantly reduced as a result of the noise averaging. The output of the ATC chain shown in Fig. 3a is preferably monitored, since only the last ATC 300n output pulse can be seen. Therefore, a signal representing the time addition of all the ATC pulses is preferably generated. For this purpose, the simple circuit shown in Fig. 4 may be used. First, the trigger input to the ATC chain is captured using a positive-edge triggered flip-flop (FF). Likewise, the end of the summation operation is captured by using a negative- edge triggered FF, generating the start and finish markers of the conversion, which are then fed to an XOR gate to generate the resulting pulse, Total ATC output. The FFs are reset after every conversion to allow multiple samples to be transmitted.

In order for the system to be extremely low in power consumption, the communication should be extremely power efficient as well. To this end, a communication scheme is proposed which is based in single-pulse harmonic modulation, which can inherently make use of time-mode signals from the ATC chain. This communication unit 510 of the system 500, together with the corresponding receiver 520 thereof is shown in Fig. 5.

The transmitter circuit 510 shown in fig. 5 uses one narrow pulse (fed to the gate of MTx) to create a wideband excitation that will get filtered by the high-Q LC-tank, creating a tone at the resonant frequency of the tank. Once the oscillation has built up, the pMOS switch (MTxd) can be turned on to drastically lower the Q of the transmitter tank, damping the oscillation and allowing for another pulse to be sent. The receiver implementation 520 fol lows a similar approach and can be seen as an envelope detector and a thresholder circuit, reusing the output bit pulses as damping signals on transistor MRxd. A maximum voltage swing may occur for a driving pulse width of exactly one half cycle (or an odd multiple of half cycles) of the tank’s resonant frequency. Therefore, the pulse width converters described above were made configurable or tunable so that process variations could be compensated.

As a result of the increased pulse width with the use of oversampling in the ATC chain, the time elapsed between the two pulses transmitted per sample increases, making the width of the damping pulse on MTxd less critical, thus allowing for complete damping of the tank’s oscillating signal between the two transmissions per sample. The resolution achieved from the chain, when considering a noiseless scenario, will depend on the receiver’s timing accuracy.

Fig. 6 shows the operation of the system for a chain of four analog- to-time converters. The chain of ATCs generates the oversampled time-mode signal at the rising edge of the trigger signal and the interface circuit generates the Total ATC Output signal. From this signal, the driving signals for the transmitter that produce the necessary oscillation at 10MHz are generated. In this simulation, a coupling factor of k=0.005 was used to model a small coupling between the coils, and an envelope detector and a limiter with a threshold of 7.5mV was used to receive the transmitted signal and convert the received signal into a marker pulse. The pulse-width of the Total ATC Output pulse and the time difference between the marker pulses differ due to the differences in the driving strengths in the designed interface circuitry appearing in the reconstructed signal as a DC offset.

Expressions such as “comprise”, “include”, “incorporate”, “contain”, “is” and “have” are to be construed in a non-exclusive manner when interpreting the description and its associated claims, namely construed to allow for other items or components which are not explicitly defined also to be present. Reference to the singular is also to be construed in be a reference to the plural and vice versa.

In the description above, it will be understood that when an element such as layer, region or substrate or components of a system are referred to as being “on”, “onto” or “connected to” another element, the element is either directly on or connected to the other element, or intervening elements may also be present.

Furthermore, the disclosed system may also be embodied with less components than provided in the embodiments described here, wherein one component carries out multiple functions. Just as well may the disclosure be embodied using more elements than depicted in the Figures, wherein functions carried out by one component in the embodiment provided are distributed over multiple components.

A person skilled in the art will readily appreciate that various parameters disclosed in the description may be modified and that various embodiments disclosed and/or claimed may be combined without departing from the scope of the invention.

It is stipulated that reference signs in the claims do not limit the scope of the claims, but are merely inserted to enhance the legibility of the claims.

Claims

1. A low-power signal acquisition system for remote biosensing, said system comprising: a converter unit, comprising a plurality of analog-to-time converters, ATCs, said ATCs being connected in cascade as a chain of ATCs, wherein said chain of ATCs is arranged for sampling and converting an input signal such as an input signal obtained from an electrode in, or on a biological tissue and wherein the voltage of the input signal is converted into an output signal of pulses with varying pulse-widths; a communication unit, arranged for communication over a short range coupling link, wherein the output signal is modulated by a modulation scheme for wireless transmission over said coupling link to a remote receiver unit for further processing of said output signal; a control unit, arranged for receiving said output signal from said chain of ATCs and for control of said communication unit to transmit said output signal; wherein said communication module comprises a pulse harmonic modulation unit arranged for driving said coupling link with a sharp impulse for generating an oscillation pulse with a rapid rise and slow decay, and wherein said unit is further arranged to generate a further oscillation pulse with a predetermined delay for suppression of said oscillation pulse for forming a bitstream between said oscillation pulse and said further oscillation pulse to transmit said digital signal to said remote receiver; and wherein said pulse harmonic modulation unit further comprises a damping switch a drive switch and an impulse generator, wherein said impulse generator is connected to the input of said pulse harmonic modulation unit for generating said narrow pulse on the basis of said input for driving said drive switch to generate said oscillation pulse, and wherein said damping switch is connected to the input of said pulse harmonic modulation unit for triggering said further oscillation pulse with said predetermined delay for suppression of said oscillation pulse; and wherein said chain of ATC’s is arranged for generating said output signal wherein the input voltage of said input signal of said electrode is modulated by a varying pulse-width of said pulses of said output signal.

2. The low-power signal acquisition system for remote biosensing according to any of the previous claims, wherein the converter unit comprises a chain of ATCs which are arranged to generate a pulse dependent on the input signal of the electrode.

3. The low-power signal acquisition system for remote biosensing according to any of the previous claims, wherein the converter unit is arranged to generate a trigger signal in between each of said ATCs.

4. The low-power signal acquisition system for remote biosensing according to any of the previous claims, wherein the trigger signal in between each of said ATCs uses a fixed-width pulse generator which is activated by the falling edge of the ATC output pulse.

5. The low-power signal acquisition system for remote biosensing according to any of the previous claims, wherein the system further comprises an interface unit arranged between said converter unit and said communication unit which is arranged to trigger signal from the chain of ATCs is captured by use of a positive- edge triggered flip-flop and wherein the end of the summation of output signal of the chain of ATCs is captured by use of a negative-edge triggered flip-flop, for generating a start and finish marker of the conversion of the input signal.

6. The low-power signal acquisition system for remote biosensing according to any of the previous claims, wherein the payload of the output signal being transmitted is comprised solely form the alternating start and finish markers of the conversion of the input signal of the converter unit.

7. The low-power signal acquisition system for remote biosensing according to any of the previous claims, wherein the system further comprises two either-edge pulse generators for generating control signals to control the driving switch for driving said coupling link.

8. The low-power signal acquisition system for remote biosensing according to any of the previous claims, wherein pulse-width of the ATCs are configurable for compensation of variation in the conversion of said input signal.

9. The low-power signal acquisition system for remote biosensing according to any of the previous claims, wherein the converter unit is comprised of a chain of at least 1 ATC, and preferably, between 2 and 1024 ATCs, more preferably between 4 and 512 ATCs, even more preferably in between 8 and 256 ATCs.

10. The low-power signal acquisition system for remote biosensing according to any of the previous claims, wherein each of said ATCs is comprised of a single PMOS transistor for tunability and variation of the generated pulse-widths, a NOR logic gate and logic inverters.

11. The low-power signal acquisition system for remote biosensing according to any of the previous claims, wherein each of the transistors of the chain of ATCs operate in near threshold region.

12. The low-power signal acquisition system for remote biosensing according to any of the previous claims, wherein the system is comprised in a wearable EEG system, preferably comprising an electrode for obtaining said input signal.

13. A signal acquisition and transmission chip, for a system according to any of the previous claims 1-10, wherein said chip is preferably a bio-implantable chip.

14. A transmission module for a low-power signal acquisition system for remote biosensing according to any of the claims 1-12, comprising a communication unit, arranged for communication over a short range coupling link communication, wherein the output signal is modulated by a modulation scheme for wireless transmission over said coupling link to a remote receiver unit for further processing of said output signal; wherein said communication unit comprises a pulse harmonic modulation unit arranged for driving said coupling link with a sharp impulse for generating an oscillation pulse with a rapid rise and slow decay, and arranged to generate a further oscillation pulse with a predetermined delay for suppression of said oscillation pulse for forming a bitstream between said oscillation pulse and said further oscillation pulse to transmit said digital signal to said remote receiver; and wherein said pulse harmonic modulation unit further comprises a damping switch a drive switch and an impulse generator, wherein said impulse generator is connected to the input of said pulse harmonic modulation unit for generating said narrow pulse on the basis of said input for driving said drive switch to generate said oscillation pulse, and wherein said damping switch is connected to the input of said pulse harmonic modulation unit for triggering said further oscillation pulse with said predetermined delay for suppression of said oscillation pulse.

15. A receiver module for a low-power signal acquisition system for remote biosensing according to any of the claims 1-13, wherein said receiver module comprising a communication unit, arranged for communication over a short range coupling link, arranged to communicate with a transmission module according to claim 14.