Patent Description:
In many applications, an array of electrodes is used for sensing a distribution of electrical signals. For instance, neural probes use an array of electrodes for sensing neuronal activities. In order to increase spatial resolution of measurements, a smaller pitch between electrodes in the array is needed. Further, having a readout circuitry on a common substrate with the electrodes provides high signal integrity when interconnecting the electrodes with the readout circuitry. However, the readout circuitry for an array of a large number of electrodes will occupy a large area and it is therefore desired that electrode signals are multiplexed such that a readout circuitry may support plural electrodes.

However, when plural electrodes are interfaced with a common instrumentation amplifier for multiplexing electrode signals in the instrumentation amplifier, the electrode signals may be degraded. In particular, in order to provide multiplexing, switches may be used for selecting which electrode signal is input to the instrumentation amplifier. When the switches are clocked in an interleaved manner, the switches together with a parasitic capacitance form a switched capacitor circuit, which results in an equivalent resistance between electrodes connected to the instrumentation amplifier. When electrode impedance is high, which in particular is true for small electrodes, signal amplitude will be degraded due to reduced equivalent input impedance of the instrumentation amplifier due to multiplexing. Also, crosstalk between electrodes will increase.

<CIT> discloses a sensing device comprising: an output area having an output circuit comprising an integrator adapted to integrate a received current so as to generate an output voltage corresponding to the received current; an electrode area comprising: an electrode comprising an exposed, electrically conductive, surface area and electrode circuitry connected to the exposed surface area, wherein the electrode circuitry comprises a voltage-to-current transducer adapted to produce a wire current corresponding to a voltage present at the exposed surface area; and a connecting wire electrically connecting the electrode circuitry to the output circuit, wherein the current received by the output circuit is the wire current.

<NPL>, <CIT>, <NPL>, <CIT>, <NPL>, <NPL>, <NPL>, <NPL>, <NPL>, <NPL> disclose input/output circuits comprising symmetrical flipped voltage followers.

An objective of the present invention is to provide an input circuitry that allows multiplexing of electrode signals while maintaining high signal integrity.

These and other objectives of the present invention are at least partly met by the invention as defined in the independent claims.

According to a first aspect, there is provided an input circuitry for receiving electrode signals, said input circuitry comprising: a plurality of channels for providing a multiplexed electrode signal input, wherein each channel comprises a multiplexing switch for selecting one channel at a time to provide electrode signal input, and wherein each channel comprises an input transistor configured to be connected to an electrode associated with the channel, wherein the input transistor is configured to receive an electrode signal at a gate of the input transistor; a reference input transistor, which is configured to be connected to a reference voltage at a gate of the reference input transistor; wherein an electrode signal received at a selected channel together with the reference voltage received at the reference input transistor form input signals to an instrumentation amplifier of the input circuitry; wherein the input circuitry is configured such that the input transistor of the selected channel forms part of a first flipped voltage follower of the instrumentation amplifier and the reference input transistor forms part of a second flipped voltage follower of the instrumentation amplifier.

The input circuitry is thus configured to receive electrode signals at different channels. Each channel comprises an input transistor, such that the electrode signals are provided at the gate of the input transistor of the respective channels. This implies that the gate of the input transistor is connected to the electrode while the channel is not selected to provide electrode signal input. Hence, the gate may follow potential variations of the electrode signal even when the channel is not selected. This implies that no input capacitance may need to be charged/discharged when an electrode signal is selected during multiplexing to avoid or at least reduce degrading of signal amplitude. Thus, the input circuitry provides high signal integrity with low crosstalk between electrodes while providing multiplexing of electrode signals.

According to an embodiment, each channel comprises a first multiplexing switch for selectively connecting or disconnecting a drain of the input transistor of the channel to a first shared node of the first flipped voltage follower.

This implies that the channels may selectively connected to a common node of the first flipped voltage follower. Hence, the first node is "shared" in that it is the node to which the drain of the input transistor of each channel is connected, when selected. However, only one channel will be selected at a time, such that multiple channels will not be simultaneously connected to the first shared node.

According to an embodiment, each channel further comprises a second multiplexing switch for selectively connecting or disconnecting the drain of the input transistor to a source of the input transistor.

The channel may be configured such that the drain of the input transistor is connected to the source of the input transistor when the channel is not selected to provide electrode signal input. Further, the channel may be configured such that the drain of the input transistor is disconnected from the source of the input transistor when the channel is selected to provide electrode signal input.

This implies that when the channel is not selected, the drain is shorted to the source in the input transistor. This implies any leakage current may be stopped.

According to an embodiment, the source of the input transistor of each channel is connected to a second shared node of the first flipped voltage follower.

The source of the input transistor of each channel may be configured to always be connected to the second shared node, regardless whether the channel is selected or not to provide electrode signal input. This implies that the source of the input transistor may follow the potential of the other electrodes instead of being floating when the channel is not selected. Thus, settling of the instrumentation amplifier to the electrode signal will be faster when the channel is selected, since less transients are induced when an electrode is selected for providing electrode signal input.

According to an embodiment, the first flipped voltage follower comprises the input transistor of the selected channel forming a first transistor of the first flipped voltage follower, a second transistor having a drain connected to a source of the first transistor, a current source connected to a drain of the first transistor and a gain element connected between the drain of the first transistor and a gate of the second transistor.

The first flipped voltage follower provides the second shared node between the drain of the second transistor and the source of the first transistor, wherein the second shared node has a voltage following the signal of the selected electrode.

Thanks to feedback of the second transistor, the second shared node will have low output impedance, providing an output to an output stage of the input circuitry with low output impedance.

The gain element may stabilize a voltage on the first shared node. This facilitates fast settling of the instrumentation amplifier to the electrode signal when a new channel is selected. Also, the gain element may ensure that the input transistor of the selected channel is in saturation mode.

According to an embodiment, an output node of the first flipped voltage follower is connected via a resistor to an output node of the second flipped voltage follower.

The output nodes of the first flipped voltage follower and the second flipped voltage follower follow the electrode signal input and the reference voltage, respectively. The resistor may thus convert an input signal voltage into current, which may be copied to the output stage.

According to an embodiment, the input circuitry further comprises an electrode offset calibration block, the electrode offset calibration block connected to opposite sides of the resistor and configured to inject a compensation current into the resistor for canceling a current jump induced by different DC offsets of electrodes when switching selection of channels.

This may ensure that a large electrode DC offset is not allowed to saturate the instrumentation amplifier.

When switching from between electrode input signals, a difference of DC electrode offsets will cause a voltage step jump at the output node of the first flipped voltage follower. Thanks to the use of the electrode offset calibration block, a compensation current may be injected into the resistor such that a current jump through the resistor due to the voltage jump at the output node of the first flipped voltage follower is canceled.

An offset calibration may be performed before electrode measurements are started, such that the DC electrode offsets may be determined. These DC electrode offsets may be stored to allow the electrode offset calibration block to provide a corresponding compensation current.

According to an embodiment, the input circuitry further comprises an output stage connected to receive signals from the first flipped voltage follower and the second flipped voltage follower.

Thus, the output stage may form a multiplexed signal such that the input circuitry may provide a multiplexed signal output from the output stage. The output stage may provide the multiplexed signals to circuitry for further processing of the electrode signals.

The output stage may comprise a capacitor for integrating the received current signal copied to the output stage. The charge sampling nature of this scheme allows the amplifier to be designed with a narrower bandwidth for the same settling accuracy compared to an instantaneous voltage sampling. Thus, aliasing of electrode noise may be reduced to avoid noise affecting quality of the output electrode signal.

According to an embodiment, the output stage comprises a reset switch for clearing signal information between readout of electrode signals of different selected channels.

The reset switch may be used to reset an integrating capacitor of the output stage between readout of signals from different channels. Thus, signal information may be easily cleared between readout of different channels.

According to an embodiment, the input circuitry comprises at least <NUM> channels.

This implies that the input circuitry and further processing circuitry which receives the multiplexed signal may be efficiently re-used. Thus, an area required by the input circuitry and further processing circuitry may be reduced by a factor <NUM> or more.

The number of electrode signals that may be multiplexed by an input circuitry may be dependent on a context in which the electrode signals are acquired. It should be realized that, if a large number of electrodes are used for sensing signals, a plurality of input circuitries may be used associated with different sets of electrodes.

According to a second aspect, there is provided a biopotential signal sensor system, comprising: the input circuitry according to the first aspect; and a plurality of electrodes configured for sensing a biopotential signal, wherein each electrode is connected to the gate of an input transistor of a channel among the plurality of channels, wherein one electrode is associated with each channel.

In many applications sensing biopotential signals, it may be interesting to detect signals from a plurality of electrodes. This may be useful for sensing distribution of biopotential within a body or for sensing biopotentials in several points of interest.

Further, when detecting biopotential signals, the electrodes are worn by a subject, and at least the input circuitry receiving the electrode signals may also need to be worn by the subject. This implies that an area required by the input circuitry affects a size of a device that is worn by the subject. Hence, in order to provide a biopotential signal sensor system that facilitates convenience to the subject from which signals are acquired, a small size of the input circuitry is desired. In this respect, the multiplexing of signals by the input circuitry, enabling the input circuitry to be shared by several electrodes facilitates a small size of a device that is to be worn by the subject.

The biopotential signal sensor system may for instance be configured to sense a biopotential signal relating to electrocardiography, electroencephalography, electrocorticography, or electromyography. However, as further discussed below, the biopotential signal sensor system may be of particular interest in a neural probe for sensing potentials in a brain, such as local field potential and action potential.

According to an embodiment, the input circuitry is arranged on a common substrate with the plurality of electrodes.

This implies that the biopotential signal sensor system may be compact. Further, it may ensure high signal integrity of the electrode signals received by the input circuitry.

According to a third aspect, the biopotential signal sensor system is a neural probe, wherein the plurality of electrodes is arranged on a carrier configured for being inserted into a brain.

Effects and features of this third aspect are largely analogous to those described above in connection with the first and second aspects. Embodiments mentioned in relation to the first and second aspects are largely compatible with the third aspect.

In neural probes, there is a desire to provide as small electrodes as possible in order to have a high spatial resolution of signals acquired from a brain. This implies that a large number of electrodes may be used, such that there may be a large need to multiplex signals in order to reduce size of an area of circuitry for processing the electrode signals.

Further, since electrodes are small, the electrodes have high impedance. Therefore, a high input impedance of the input circuitry is desired so as not to degrade signal quality of the electrode signals. Hence, the input circuitry is well-suited for use in a neural probe, since the input circuitry may maintain a high input impedance even though multiplexing is used.

According to a fourth aspect, there is provided a method for amplifying electrode signals, said method comprising: receiving electrode signals on a plurality of channels of an amplifying input circuitry for providing multiplexed amplifying of the electrode signals, wherein each channel comprises an input transistor configured to be connected to an electrode associated with the channel, wherein the input transistor is configured to receive an electrode signal at a gate of the input transistor; selecting a first electrode signal as input to multiplexed amplifying by connecting the input transistor of a first channel to form part of a first flipped voltage follower of an instrumentation amplifier and by all other channels being deselected, the first electrode signal forming an input signal pair together with a reference voltage signal to the instrumentation amplifier; and selecting a second electrode signal as input to multiplexed amplifying by connecting the input transistor of a second channel to form part of the first flipped voltage follower of the instrumentation amplifier and by all other channels being deselected, the second electrode signal forming an input signal pair together with the reference voltage signal to the instrumentation amplifier.

Effects and features of this fourth aspect are largely analogous to those described above in connection with the first, second, and third aspects. Embodiments mentioned in relation to the first, second, and third aspects are largely compatible with the fourth aspect.

Each channel comprises an input transistor, such that the electrode signals are provided at the input transistor of the respective channels, even when the channel is not selected to provide electrode signal input to the amplifying circuitry. The electrode signal may be provided at a gate of the input transistor. This implies that no input capacitance may need to be charged/discharged when an electrode signal is selected during multiplexing to avoid or at least reduce degrading of signal amplitude. Thus, the method may ensure high signal integrity while providing multiplexing of electrode signals.

The method may be controlled by a control unit, which may provide clocking signals for synchronizing selecting of an electrode signal of one channel and deselecting all other channels.

The selecting and deselecting of an electrode signal of a channel may be performed by turning on and off a first multiplexing switch.

The method may further comprise connecting a drain of the input transistor to a source of the input transistor when a channel is deselected. This implies that when the channel is not selected, the drain is shorted to the source in the input transistor. This implies any leakage current may be stopped.

The connecting of the drain of the input transistor to the source of the input transistor may be performed by turning on a second multiplexing switch. Further, when the channel is selected, the second multiplexing switch may be turned off to disconnect the drain of the input transistor from the source of the input transistor.

According to an embodiment, the method further comprises, when selecting the second electrode signal, providing a reset signal to an output stage of the instrumentation amplifier for clearing signal information between readout of electrode signals of different selected channels.

The above, as well as additional objects, features and advantages of the present invention, will be better understood through the following illustrative and non-limiting detailed description, with reference to the appended drawings.

Referring now to <FIG>, an input circuitry <NUM> for receiving electrode signals according to an embodiment will be described. The input circuitry <NUM> is configured to receive signals from a plurality of electrodes <NUM> and the input circuitry <NUM> is configured to form multiplexed signal from the signals of the plurality of electrodes <NUM>.

The electrodes <NUM> may be any type of electrode <NUM> which is configured to sense an electrical potential at a location of the electrode <NUM>. The electrode <NUM> may therefore comprise a conducting part which is configured to sense the electrical potential. The electrode <NUM> could for instance be used for sensing biopotential, i.e. an electrical potential in a body of a human being or an animal. However, the electrode <NUM> could be used in numerous other applications.

The input circuitry <NUM> comprises a plurality of channels <NUM>, wherein each channel is associated with one electrode <NUM>. Each channel <NUM> comprises an input transistor <NUM>. The electrode <NUM> associated with the channel <NUM> is connected to a gate of the input transistor <NUM>, such that an electrode signal from the electrode <NUM> is received at the gate.

The input circuitry <NUM> is configured to select one channel <NUM> at a time to provide electrode signal input to the input circuitry <NUM>. Thus, at each time instant, one channel may be selected while all other channels may be deselected.

Each channel <NUM> may comprise a first multiplexing switch <NUM>, which is configured to select the electrode signal of the channel <NUM> to provide the electrode signal input of the input circuitry <NUM>.

The gate of the input transistor <NUM> is connected to the electrode <NUM>, even when the channel <NUM> is not selected. This implies that the gate of the input transistor <NUM> may follow the potential variations of the electrode signal from the electrode <NUM> associated with the channel <NUM> even when the channel <NUM> is not selected. Hence, no charge/discharge from the electrode <NUM> is required when the channel <NUM> is selected, such that signal amplitude is not degraded.

The electrode signal provided at the gate of the input transistor <NUM> of the selected channel <NUM> together with a reference voltage forms a pair of input signals to an instrumentation amplifier of the input circuitry <NUM>. The input circuitry <NUM> may further comprise a reference input transistor <NUM> which is configured to receive the reference voltage at a gate of the reference input transistor <NUM>. The reference voltage may be received by the reference input transistor <NUM> being connected to a reference electrode or to a known potential, such as ground.

The input circuitry <NUM> forms a first flipped voltage follower <NUM> with the input transistor <NUM> of the selected channel forming a first transistor of the first flipped voltage follower <NUM>. The input circuitry <NUM> further comprises a second flipped voltage follower <NUM> with the reference input transistor <NUM> forming a first transistor of the second flipped voltage follower.

The first flipped voltage follower <NUM> is configured to receive the electrode signal input (at the selected channel <NUM>) and is configured to provide a potential following the potential of the electrode signal input at a first output node <NUM>. The second flipped voltage follower <NUM> is configured to provide a potential following the potential of the reference voltage at a second output node <NUM>.

The first and second output nodes <NUM> and <NUM> are arranged on opposite sides of a resistor <NUM>, such that the voltage across the resistor <NUM> is converted to a current. The current is copied to an output stage <NUM> of the input circuitry <NUM>.

The input circuitry <NUM> further comprises an electrode offset calibration block <NUM>, which is connected to opposite sides of the resistor <NUM>. The electrode offset calibration block <NUM> is configured to inject a compensation current into the resistor <NUM> for canceling a current jump induced by different DC offsets of the electrodes <NUM> when switching selection of channels <NUM>.

An offset calibration may be performed before receipt of electrode signals from the electrodes <NUM> are started, such that the DC electrode offsets may be determined for each of the electrodes <NUM>. These DC electrode offsets may be stored to allow the electrode offset calibration block <NUM> to provide a corresponding compensation current.

The electrode offset calibration block <NUM> may be configured to receive a digital signal corresponding to the stored DC electrode offset for a selected electrode <NUM> and may convert the received digital signal to an analog compensation current to be injected into the resistor <NUM>.

The current through the resistor <NUM> flows through a second transistor <NUM> of the first flipped voltage follower <NUM> and through a second transistor <NUM> of the second flipped voltage follower <NUM>. The signal on a gate of the second transistor <NUM> of the first flipped voltage follower <NUM> is also provided to a gate of a first transistor <NUM> of the output stage <NUM>. The signal on a gate of the second transistor <NUM> of the second flipped voltage follower <NUM> is also provided to a gate of a second transistor <NUM> of the output stage <NUM>. Thus, the current flowing through the resistor <NUM>, the second transistor <NUM> of the first flipped voltage follower and the second transistor <NUM> of the second flipped voltage follower is copied to the output stage <NUM>.

The output stage <NUM> comprises a capacitor <NUM>, which is configured to receive the current copied from the resistor <NUM>. The capacitor <NUM> is configured to integrate the received current signal. The charge sampling nature of this scheme allows the input circuitry <NUM> to be designed with a narrower bandwidth for the same settling accuracy compared to an instantaneous voltage sampling. Thus, aliasing of electrode noise may be reduced to avoid noise affecting quality of the output electrode signal.

Output nodes <NUM>, <NUM> are connected on opposite sides of the capacitor <NUM> for providing a differential output signal from the output stage <NUM> of the input circuitry <NUM>. The output stage <NUM> further comprises a reset switch <NUM>. The reset switch <NUM> is configured to be enabled when a new electrode <NUM> is selected to provide the electrode signal input. The reset switch <NUM> clears the signal information between readout of different channels <NUM>. Also, the reset switch <NUM> may isolate the output nodes <NUM>, <NUM> from any glitched due to the switching between channels <NUM>.

Referring now to <FIG>, an embodiment for selection of channels <NUM> among N channels, where N is an integer number, will be further described. In each of <FIG>, a first channel <NUM> associated with a first electrode 102a, a second channel 110b associated with a second electrode 102b, and an N'th channel 110n associated with an N'th electrode 102n are shown.

Each channel <NUM> comprises the first multiplexing switch <NUM>. The first multiplexing switch is configured to selectively connect or disconnect a drain of the input transistor <NUM> to a first shared node <NUM> of the first flipped voltage follower <NUM>. The first node <NUM> is "shared" in that it is the node to which the drain of the input transistor <NUM> of each channel <NUM> is connected, when selected. However, only one channel <NUM> will be selected at a time, such that multiple channels will not be simultaneously connected to the first shared node <NUM>.

When the first multiplexing switch <NUM> of a channel <NUM> is turned on to select the channel <NUM>, the input transistor <NUM> of the channel <NUM> forms part of the first flipped voltage follower <NUM>, by the drain of the input transistor <NUM> being connected to the first shared node <NUM>, which is part of the first flipped voltage follower <NUM>.

Each channel <NUM> may further be connected to a second shared node <NUM>, which corresponds to the first output node <NUM> of the first flipped voltage follower <NUM>. The source of the input transistor <NUM> may be connected to the second shared node <NUM>, even when the channel <NUM> is not selected. This implies that the source of the input transistor <NUM> follows potentials of the other electrodes <NUM> instead of being floating when the channel <NUM> is not selected. This implies that settling to the electrode signal will be fast when the channel <NUM> is selected, since less transients are induced when an electrode <NUM> is selected for providing electrode signal input.

Each channel <NUM> may further comprise a second multiplexing switch <NUM>. The second multiplexing switch <NUM> may selectively connect or disconnect the drain of the input transistor <NUM> to the source of the input transistor <NUM>. When a channel <NUM> is not selected, the drain is shorted to the source of the input transistor <NUM> by the second multiplexing switch <NUM> being turned on. This implies that any leakage current from the input transistor <NUM> affecting readout of an electrode signal of another channel <NUM> may be stopped.

<FIG> illustrates a point in time when the first channel 110a is selected for providing electrode signal input from the electrode 102a. At the point in time illustrated in <FIG>, a clocking signal controlling the first multiplexing switch <NUM> of the first channel 110a is high and a clocking signal controlling the second multiplexing switch <NUM> of the first channel 110a is low. This implies that the drain is disconnected from the source of the input transistor <NUM> in the first channel 110a and the drain of the input transistor <NUM> of the first channel 110a is connected to the first shared node <NUM>.

Further, at the point in time illustrated in <FIG>, clocking signals controlling the first multiplexing switches <NUM> of all the remaining channels, illustrated by channels 110b, 110n, are low to disconnect the drain of the input transistors <NUM> of these channels 110b, 110n from the first shared node <NUM>. Also, clocking signals controlling the second multiplexing switches <NUM> of all the remaining channels, illustrated by channels 110b, 110n, are high to short the drain to the source of the input transistors <NUM> of these channels <NUM>.

<FIG> illustrates a point in time when the second channel 110b is selected for providing electrode signal input from the electrode 102a. At the point in time illustrated in <FIG>, the clocking signal controlling the first multiplexing switch <NUM> of the second channel 110b is high and the clocking signal controlling the second multiplexing switch <NUM> of the second channel 110b is low. This implies that the drain is disconnected from the source of the input transistor <NUM> in the second channel 110b and the drain of the input transistor <NUM> of the second channel 110b is connected to the first shared node <NUM>.

Further, at the point in time illustrated in <FIG>, clocking signals controlling the first multiplexing switches <NUM> of all the remaining channels, illustrated by channels 110a, 110n, are low to disconnect the drain of the input transistors <NUM> of these channels 110a, 110n from the first shared node <NUM>. Also, clocking signals controlling the second multiplexing switches <NUM> of all the remaining channels, illustrated by channels 110a, 110n, are high to short the drain to the source of the input transistors <NUM> of these channels <NUM>.

The channels <NUM> may be sequentially selected one by one to provide the electrode signal input in a multiplexed manner. <FIG> illustrates a point in time when the N'th channel 110n is selected for providing electrode signal input from the electrode 102n. At the point in time illustrated in <FIG>, the clocking signal controlling the first multiplexing switch <NUM> of the N'th channel 110n is high and the clocking signal controlling the second multiplexing switch <NUM> of the N'th channel 110n is low. This implies that the drain is disconnected from the source of the input transistor <NUM> in the N'th channel 110n and the drain of the input transistor <NUM> of the N'th channel 110n is connected to the first shared node <NUM>.

Further, at the point in time illustrated in <FIG>, clocking signals controlling the first multiplexing switches <NUM> of all the remaining channels, illustrated by channels 110a, 110b, are low to disconnect the drain of the input transistors <NUM> of these channels 110a, 110b from the first shared node <NUM>. Also, clocking signals controlling the second multiplexing switches <NUM> of all the remaining channels, illustrated by channels 110a, 110b, are high to short the drain to the source of the input transistors <NUM> of these channels <NUM>.

Once all channels 110a, 110b, 110n have been selected to provide electrode signal input, the first channel 110a may again be selected, such that a new sequence of sequentially selecting each channel 110a, 110b, 110n one at a time may be initiated.

Referring now to <FIG>, the first flipped voltage follower <NUM> according to an embodiment will be described in further detail.

The flipped voltage follower <NUM> is formed by the input transistor <NUM> of the selected channel <NUM> (forming a first transistor <NUM>), the second transistor <NUM>, a current source <NUM>, and a gain element <NUM>. The first transistor <NUM> and the second transistor <NUM> may be p-type metal-oxide-semiconductor (PMOS) transistors.

The current source <NUM> enables a current through the first transistor <NUM> to be held stable, independent of an output current from the flipped voltage follower.

The output node <NUM> is arranged between a drain of the second transistor <NUM> and a source of the first transistor <NUM>. The output node <NUM> will have a potential following the electrode signal received at the gate of the first transistor <NUM>.

The second transistor <NUM> provides feedback of the flipped voltage follower <NUM>. The output node <NUM> will have a low output impedance because of the feedback of the second transistor <NUM>.

The signal on the first shared node <NUM> is passed through a gain element <NUM> to be provided to a gate of the second input transistor <NUM>. The signal on the first shared node <NUM> will have a small ac component due to attenuation of the gain element <NUM>. Thanks to use of the gain element <NUM>, it is easy to maintain the first transistor <NUM> in saturation mode and also to provide a fast settling time during multiplexing.

As shown in enlargement in <FIG>, the gain element <NUM> may comprise an n-type metal-oxide-semiconductor (NMOS) transistor <NUM>, with the source connected to the first shared node <NUM> and the drain connected to the gate of the second transistor <NUM>. The NMOS transistor <NUM> may further receive a bias voltage on a gate of the NMOS transistor <NUM>.

The second flipped voltage follower <NUM> may be configured in a corresponding manner, receiving the reference voltage at the reference input transistor <NUM>. As shown in <FIG>, the second flipped voltage follower <NUM> may thus comprise the reference input transistor <NUM>, the second transistor <NUM>, a current source <NUM>, and a gain element <NUM>.

Referring now to <FIG> and <FIG>, a method according to an embodiment will be described in relation to a flow chart in <FIG> and a clocking diagram illustrating signals of switches in <FIG>.

The method comprises receiving <NUM> electrode signals on a plurality of channels <NUM> of the amplifying input circuitry <NUM> for providing multiplexed amplifying of the electrode signals.

The method further comprises selecting <NUM> a first electrode signal as input to multiplexed amplifying by connecting the input transistor <NUM> of the first channel 110a to form part of the first flipped voltage follower <NUM> of the instrumentation amplifier and by all other channels 110b, 110n being deselected. Thus, the first electrode signal forms an input signal pair together with the reference voltage signal to the instrumentation amplifier.

As shown in <FIG>, a first clocking signal <NUM> for controlling the first multiplexing switch <NUM> of the first channel 110a is thus set to be high, while the clocking signals <NUM>, <NUM> for controlling the first multiplexing switch <NUM> of remaining channels 110b, 110n are low, during a first period of time <NUM>. Thus, the first electrode 102a is selected to provide the electrode signal input during the first period of time <NUM>.

The method further comprises selecting <NUM> a second electrode signal as input to multiplexed amplifying by connecting the input transistor <NUM> of the second channel 110b to form part of the first flipped voltage follower <NUM> of the instrumentation amplifier and by all other channels 110a, 110n being deselected. Thus, the second electrode signal forms an input signal pair together with the reference voltage signal to the instrumentation amplifier.

As shown in <FIG>, the second clocking signal <NUM> for controlling the first multiplexing switch <NUM> of the second channel 110b is thus set to be high, while the clocking signals <NUM>, <NUM> for controlling the first multiplexing switch <NUM> of remaining channels 110a, 110n are low, during a second period of time <NUM>. Thus, the second electrode 102b is selected to provide the electrode signal input during the second period of time <NUM>.

Further, the selection of electrodes to provide the electrode signal input proceeds until all electrodes have been selected. Thus, in a N'th period of time <NUM>, the N'th clocking signal <NUM> for controlling the first multiplexing switch <NUM> of the N'th channel 110n is thus set to be high, while the clocking signals <NUM>, <NUM> for controlling the first multiplexing switch <NUM> of remaining channels 110a, 110b are low.

As can be seen in <FIG>, the electrodes <NUM> and their associated input transistors <NUM> are connected into the instrumentation amplifier in a time interleaved manner controlled by the clocking signals <NUM>, <NUM>, <NUM>. The clocking signal <NUM>, <NUM>, <NUM> controlling a first multiplexing switch <NUM> will be high during a single period of time, when the electrode associated with the channel controlled by the clocking signal is selected, and will then be low during multiple periods of time when electrodes associated with other channels are selected.

Although not shown in <FIG>, clocking signals controlling the second multiplexing switch <NUM> of each channel may also be synchronized with the clocking signals <NUM>, <NUM>, <NUM>. The clocking signal controlling the second multiplexing switch <NUM> will be low during a single period of time, when the electrode associated with the channel controlled by the clocking signal is selected, and will then be high during multiple periods of time when electrodes associated with other channels are selected.

During each transition from a current electrode being selected to a next electrode being selected, a reset signal <NUM> is enabled to turn on the reset switch <NUM> and reset the capacitor <NUM>, which clears the signal information of the current electrode. Also, at each transition, digital signal input to the electrode offset calibration block <NUM> is updated to a signal associated with the next electrode.

Referring now to <FIG>, a biopotential signal sensor system <NUM> according to an embodiment will be described.

The biopotential signal sensor system <NUM> comprises a plurality of electrodes <NUM> configured for sensing a biopotential signal, which may correspond to the plurality of electrodes <NUM> described above. The biopotential signal sensor system <NUM> further comprises input circuitry for receiving the biopotential signals from the electrodes <NUM> and for providing multiplexed amplifying of the biopotential signals. The biopotential signal sensor system <NUM> may thus comprise the input circuitry <NUM> according to the embodiment described above.

The biopotential signals from the electrodes <NUM> may each be connected to the gate of the input transistor <NUM> of a respective channel <NUM> of the input circuitry <NUM>. Thus, the input circuitry <NUM> may allow multiplexing of the biopotential signals.

The biopotential signal sensor system <NUM> may be configured to be worn by a subject. The biopotential signal sensor system <NUM> may thus comprise a carrier configured for attachment to the subject or for arrangement around a body part of the subject. For instance, the biopotential signal sensor system <NUM> may comprise a patch <NUM> for attaching the biopotential signal sensor system <NUM> to the subject.

The biopotential signal sensor system <NUM> may comprise further processing circuitry for further processing of the multiplexed electrode signals output by the input circuitry <NUM>. Thus, the biopotential signal sensor system <NUM> may provide analysis of the electrode signals.

The biopotential signal sensor system <NUM> may also or alternatively comprise a communication unit for wired or wireless communication to a remote unit for further processing of the electrode signals. The biopotential signal sensor system <NUM> may communicate the multiplexed electrode signals output by the input circuitry <NUM> to the remote unit or may further process the multiplexed electrode signals before communicating the further processed signals to the remote unit.

The input circuitry <NUM> may be arranged on a common substrate <NUM> with the plurality of electrodes <NUM>. This implies that the biopotential signal sensor system <NUM> may be compact. Further, it may ensure high signal integrity of the electrode signals received by the input circuitry <NUM>.

The biopotential signal sensor system <NUM> may for instance be configured to sense a biopotential signal relating to electrocardiography, electroencephalography, electrocorticography, or electromyography.

Referring now to <FIG>, a neural probe <NUM> according to an embodiment will be described. The neural probe <NUM> may incorporate electrodes and input circuitry of the biopotential signal sensor system <NUM> as described above.

In the neural probe <NUM>, small electrodes <NUM> are used in order to have a high spatial resolution of signals acquired from a brain. This implies that a large number of electrodes <NUM> may be used, such that there may be a large need to multiplex signals in order to reduce size of an area of circuitry for processing the electrode signals.

Further, since electrodes <NUM> are small, the electrodes <NUM> have high impedance. Therefore, a high input impedance of the input circuitry <NUM> is desired so as not to degrade signal quality of the electrode signals. Hence, the input circuitry <NUM> as described above is well-suited for use in the neural probe <NUM>, since the input circuitry <NUM> may maintain a high input impedance even though multiplexing is used.

The electrodes <NUM> may be arranged on a carrier <NUM> configured for being inserted into the brain to allow the electrodes <NUM> to acquire signals from the brain. The carrier <NUM> may have a pointed tip <NUM> for facilitating insertion into the brain and may have a base portion <NUM> which is intended not to be inserted into the brain.

The electrodes <NUM> are arranged in the portion of the carrier <NUM> intended to be inserted into the brain. The input circuitry <NUM> may be arranged in the portion of the carrier <NUM> intended to be inserted into the brain, such that the input circuitry <NUM> may be arranged in a layer below the electrodes <NUM>, illustrated as dashed lines for an input circuitry <NUM> supporting the electrodes <NUM> above the input circuitry <NUM>. According to an alternative, the input circuitry <NUM> may be arranged in the base portion <NUM> so as to enable minimizing a size of a part the neural probe <NUM> to be inserted into the brain.

The electrodes <NUM> and the input circuitry <NUM> may still be arranged on a common substrate to ensure high signal integrity of the electrode signals received by the input circuitry <NUM>.

Claim 1:
An input circuitry for receiving electrode signals, said input circuitry (<NUM>) comprising:
a plurality of channels (<NUM>) for providing a multiplexed electrode signal input, wherein each channel (<NUM>) comprises a multiplexing switch (<NUM>) for selecting one channel (<NUM>) at a time to provide electrode signal input, and wherein each channel (<NUM>) comprises an input transistor (<NUM>) configured to be connected to an electrode (<NUM>; <NUM>; <NUM>) associated with the channel (<NUM>), wherein the input transistor (<NUM>) is configured to receive an electrode signal at a gate of the input transistor (<NUM>);
characterised in that the input circuitry further comprises:
a reference input transistor (<NUM>), which is configured to be connected to a reference voltage at a gate of the reference input transistor (<NUM>);
wherein an electrode signal received at a selected channel (<NUM>) together with the reference voltage received at the reference input transistor (<NUM>) form input signals to an instrumentation amplifier of the input circuitry (<NUM>);
wherein the input circuitry (<NUM>) is configured such that the input transistor (<NUM>) of the selected channel (<NUM>) forms part of a first flipped voltage follower (<NUM>) of the instrumentation amplifier and the reference input transistor (<NUM>) forms part of a second flipped voltage follower (<NUM>) of the instrumentation amplifier.