Patent Application
20250073450
The present application is a non-provisional patent application claiming priority to application No. EP 23193810.1, filed Aug. 29, 2023, the contents of which are hereby incorporated by reference.
The present disclosure provides a neuromodulation device for measuring a biological electrical signal in response to a neural modulation of biological tissue. The amplifier circuit provided by this disclosure is configured to suppress a common mode (CM) voltage signal in the input voltage signal, and consequently to reduce CM interference (CMI).
A bi-directional (i.e., closed loop) neural interface may be used by a device to perform both neural stimulation and recording. Such a device enables neuromodulation—i.e., is referred to as a neuromodulation device—which is useful for neuroscience studies and treatments of neurological disorders.
For performing the neural recording, an amplifier circuit (also referred to as neural amplifier) is required, and should be able to perform low-noise small-signal amplification, while at the same time rejecting a large electrode DC offset (EDO). To achieve the desired EDO rejection ability, capacitively coupled architectures have been widely adopted for such amplifier circuits, since the input capacitors exhibit infinite impedance at DC, and thus prevent the EDO from being amplified. To achieve the low-noise performance, a differential inverter-based transconductor is advantageously used in the amplifier circuit, since it provides a higher transconductance than other well-known types of transconductor (e.g., simple wide-swing, or folded cascode).
An example of a conventional capacitively coupled amplifier circuit that may be used in a neuromodulation device is shown in
In particular, during performing the neural stimulation, depending on the distance between the place of stimulation to recording electrodes, and on how strong the stimulation signal is, the stimulation signal can partially propagate to the input (recording and reference electrodes) of the amplifier circuit of
To address this problem, a CM feedforward (CMFF) amplifier may be inserted into the amplifier circuit, as shown in
However, the additional CMFF amplifier shown in
The present disclosure provides an amplifier circuit for a neuromodulation device, in particular, to overcome the above-mentioned issues. In some example embodiments, the present disclosure provides for the suppression of a CM voltage signal and reduction of CMI, while keeping the size of the amplifier circuit small. A further objective is to avoid input impedance degradation. In some example embodiments, the present disclosure provides for the performance of the amplifier circuit for low-noise small-signal amplification, and that the amplifier circuit at the same time rejects large EDO. Another objective of this disclosure is to provide an improved neuromodulation device.
In some example embodiments, the present disclosure provides an amplifier circuit for amplifying a biological electrical signal, the amplifier circuit comprising: an input stage with two input terminals, configured to receive an input voltage signal, which is based on the biological electrical signal and comprises a CM voltage signal and a differential mode (DM) voltage signal; a differential transconductor comprising a non-inverting input and an inverting input, each connected to one of the two input terminals, and comprising an output for providing an output current signal based on the DM voltage signal; wherein the transconductor is configured to provide a first CM voltage signal, which is tapped after the non-inverting input, and a second CM voltage signal, which is tapped after the inverting input; and a CM amplifier configured to combine the first CM voltage signal with the second CM voltage signal to obtain a combined CM voltage signal, amplify the combined CM voltage signal with an inverting gain to obtain an inverted CM voltage signal, and provide the inverted CM voltage signal to the non-inverting input and the inverting input of the transconductor.
In some example embodiments, the CM amplifier of the amplifier circuit suppresses the CM voltage signal in the input signal and reduces CMI. Since the amplifier circuit comprises the CM amplifier after the transconductor, input impedance degradation is avoided. Also, the size of the amplifier circuit can be smaller than, for example, the amplifier circuit shown in
In some example embodiments, the amplifier circuit comprises: a first capacitive feedback line configured to feedback the inverted CM voltage signal from the CM amplifier to the non-inverting input of the transconductor; and a second capacitive feedback line configured to feedback the inverted CM voltage signal from the CM amplifier to the inverting input of the transconductor; wherein each of the first and the second capacitive feedback line comprises a first capacitor.
In some example embodiments of the amplifier circuit, each of the non-inverting input and the inverting input of the transconductor is connected to one of the two input terminals of the input stage via a respective second capacitor; and the second capacitor has a higher capacitance than the first capacitor.
In some example embodiments, the capacitive feedback from the CM amplifier as disclosed leads to low noise in the amplifier circuit.
In some example embodiments of the amplifier circuit, the transconductor comprises: a first transistor connected with its gate to the non-inverting input and coupled with its source to a supply voltage, VDD; a second transistor connected with its gate to the inverting input, connected with its source to the source of the first transistor, and coupled with its source to VDD; a third transistor connected with its gate to the non-inverting input, connected with its drain to the drain of the first transistor, and coupled with its source to a ground voltage; and a fourth transistor connected with its gate to the inverting input, connected with its drain to the drain of the second transistor, connected with its source to the source of the third transistor, and coupled with its source to VSS; wherein the first CM voltage signal is tapped between the sources of the first and the second transistor, and the second CM voltage signal is tapped between the sources of the third and the fourth transistor.
In some example embodiments, the amplifier circuit is configured such that a tail current of the source-connected third and fourth transistor is higher than a tail current of the source-connected first and second transistor in use of the amplifier circuit. This allows folded-cascode branches to deliver the output current signal of the amplifier circuit.
In some example embodiments of the amplifier circuit, the CM amplifier comprises a summing junction at which the first CM voltage signal and the second CM voltage signal are combined into the combined CM voltage signal; wherein each of the first CM voltage signal and the second CM voltage signal is connected to the combination point via a respective third capacitor.
In some example embodiments of the amplifier circuit, the CM amplifier further comprises a gain circuit including a second transconductor, a fourth capacitor and a first resistor; and the gain circuit is configured to amplify the combined CM voltage signal with the inverting gain to produce the inverted CM voltage signal.
In some example embodiments, the amplifier circuit further comprises a DM feedback circuit configured to provide a feedback voltage signal, which is based on the output current signal of the transconductor, to the non-inverting input and the inverting input of the transconductor.
In some example embodiments of the amplifier circuit, the DM feedback circuit comprises a first capacitive feedback path and a second capacitive feedback path; and each capacitive feedback path comprises a respective fifth capacitor that is connected in parallel to a respective second resistor. The example capacitively coupled feedback architecture achieves the desired EDO rejecting abilities of the amplifier circuit.
In some example embodiments, the amplifier circuit further comprises a conversion circuit configured to convert the output current signal of the transconductor into the feedback voltage signal.
In some example embodiments of the amplifier circuit, the biological electrical signal is an electroencephalogram, (EEG) signal or a stimulation-based neural signal.
In some example embodiments of this disclosure provides a neuromodulation device for measuring one or more biological electrical signals in response to a neural modulation of biological tissue, wherein the neuromodulation device comprises one or more amplifier circuits of the first aspect or any implementation thereof.
In some example embodiments, the neuromodulation device further comprises an array of electrodes comprising a first set of electrodes and a second set of electrodes, wherein each electrode of the first set is connected to a respective amplifier circuit of the one or more amplifier circuits, and wherein each electrode of the second set is configured to cause a respective neural modulation of the biological tissue. That is, some electrodes can be used for recording, and some other electrodes for stimulating, which may be beneficial for the performance of the neuromodulation device.
In some example embodiments of the neuromodulation device, each electrode of the second set comprises a stimulator, which is configured to provide a stimulation signal to cause the neural modulation of the biological tissue.
In some example embodiments, the neuromodulation device comprises multiple of the amplifier circuits; wherein the amplifier circuits share a single CM amplifier; and the CM amplifier is configured to provide, for each of the amplifier circuits, a respective inverted CM voltage signal to the non-inverting input and the inverting input of the transconductor of that amplifier circuit. This allows reducing the size of the neuromodulation device significantly, in particularly, reducing the area per channel.
In some example embodiments, the neuromodulation device further comprises one or more shared buffers connected to the multiple amplifier circuits and to the single CM amplifier, wherein the output of each amplifier circuit is connected by a respective switch to the shared buffers; wherein the neuromodulation device is configured to sequentially operate the switches, which causes the multiple amplifier circuits to sequentially output their respective current signal and causes the CM amplifier to sequentially provide the respective inverted CM voltage signal to the respective transconductor of one of the amplifier circuits. The shared buffers allow multiplexing the multiple channels.
In some example embodiments, the neuromodulation device further comprises a bi-directional neural interface comprising at least one needle; wherein the neural interface is configured to provide the neural stimulation to the biological tissue, to receive the one or more biological electrical signals, and to provide them to the one or more amplifier circuits.
The above, as well as additional objects, features and advantages of the present disclosure, will be better understood through the following illustrative and non-limiting detailed description, with reference to the appended drawings. In the drawings like reference numerals will be used for like elements unless stated otherwise.
In cooperation with attached drawings, the technical contents and detailed description of the embodiments are described thereinafter according to an example embodiment, being not used to limit the claimed scope. This disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the concepts for which protection is sought.
The amplifier circuit 20 shown in
The input stage 21 is configured to receive an input voltage signal 22, which is based on the biological electrical signal that the amplifier circuit 20 is intended to amplify. For instance, the input voltage signal 22 may be derived from the biological electrical signal, or may be the biological electrical signal, or the biological electrical signal may be signal processed to obtain the input voltage signal 22. The input voltage signal 22 comprises a CM voltage signal and a DM voltage signal. The DM voltage signal is the signal component, which the amplifier circuit 20 is supposed to amplify, while the CM voltage signal is the signal component that the amplifier circuit 20 is designed to suppress.
The differential transconductor 23 comprises a non-inverting input and an inverting input, like a differential amplifier. Each input of the transconductor 23 is connected to one of the two input terminals, i.e., the input voltage signal 22 is provided to the differential transconductor 23. The transconductor 23 further comprises an output 24, which is configured to provide an output current signal of the amplifier circuit 20, wherein the output current signal is based on the DM voltage signal. For instance, the output current signal may amplify the DM voltage signal. The amplifier circuit 20 is further configured to suppress the CM voltage signal in the input voltage signal 22 from appearing or at least substantially influencing the output current signal.
To this end, the transconductor 23 is configured to provide a first CM voltage signal 25 and a second CM voltage signal 26 to the CM amplifier 27. The first CM voltage signal is tapped after the non-inverting input, for instance, between the non-inverting input and the output 24 of the transconductor 23. The second CM voltage signal 26 is tapped after the inverting input, for instance, between the inverting input and the output 24 of the transconductor 23. Exemplary details where the CM voltage signals 25, 26 are tapped are provided below.
The CM amplifier 27 is configured to combine the first CM voltage signal 25 with the second CM voltage signal 26, so as to obtain a combined CM voltage signal. For instance, the first and second CM voltage signal 25, 26 may be summed. Then, the CM amplifier 27 is configured to amplify the combined CM voltage signal with an inverting gain, so as to obtain an inverted CM voltage signal 28. This inverted CM voltage signal 28 is then provided back to the non-inverting input and the inverting input of the transconductor 23, respectively, as indicated in
The amplifier circuit 20 shown in
The amplifier circuit 20 comprises further capacitors. For instance, the amplifier circuit 20 comprises a capacitor CL at the output 24, in particular, between two output terminals of the output 24. Further, the amplifier circuit 20 comprises two capacitors Cin. Namely, both the non-inverting input and the inverting input of the transconductor 23 may be connected via one capacitor Cin to the input stage 21. The capacitors Cin may be selected such that they have (each) a higher capacitance than the capacitors Cco.
The amplifier circuit 20 further comprises a DM feedback circuit 33, which is configured to provide a feedback voltage signal 34, which is based on the output current signal of the transconductor 23—which is again based on the DM voltage signal in the input voltage signal 22—to the two inputs of the transconductor 23. The DM feedback circuit 33 comprises a first and a second capacitive feedback path, wherein each feedback path comprises a capacitor Cf and a resistor Rf that is connected in parallel to Cf.
As can be seen in
Further, the gates of the first transistor M1 and the third transistor M3 are both connected to the non-inverting input, and the gates of the second transistor M2 and the fourth transistor M4 are both connected to the inverting input. Moreover, the connected sources of the first transistor M1 and the second transistor M2 are further coupled to VDD, e.g., via a current source, and the connected sources of the third transistor M3 and the fourth transistor M4 are further coupled to VSS, e.g., via a current source. Notably, in this disclosure “connected” typically denotes a direct electrical connection between two components, while “coupled” denotes and indirect connection, for instance, via one or more other components.
In the exemplary amplifier circuit 20 of
These CM voltage signals 25, 26 are provided to the CM amplifier 27, in particular, are routed to a summing junction 42. The lines carrying the first CM voltage signal 25 and the second CM voltage signal 26 may be respectively connected to the summing junction 42 via a respective capacitor Cci. At the summing junction 42, the first CM voltage signal 25 and the second CM voltage signal 26 are combined, i.e., added together. This results in the combined CM voltage signal. The combined CM voltage signal is further provided to a gain circuit 43 of the CM amplifier 27. The gain circuit 43 includes a transconductor AC, a capacitor Ccf and a resistor Rcf as shown, and is configured to amplify the combined CM voltage signal with the inverting gain (negative gain), which results in the inverted CM voltage signal 28. The inverted voltage signal 28 is provided via the capacitive feedback lines 31, 32 to the inverting and non-inverting input of the transconductor 23.
An underlying concept of the amplifier circuits 20 shown in the
The transconductor 23 (also labelled with A in the
V
CO
=−KV
ci
=−K(VcmH+VcmL)=−KViCM.
In the above formula, ViCM1=ViCM2≅2VcmH≅2VcmL. The inverted CM voltage signal 28 is fed back to the input terminals of the transconductor 23, via the feedback lines 31, 32 including the capacitors CCO. This feedback mechanism creates a large equivalent capacitance CEQ to ground, as seen by the CM voltage signals which is defined by:
With this large equivalent capacitance CEQ, and for K>>1, the signal ViCM can be calculated by:
For the ideal case that K=∞, ViCM becomes zero, meaning that there are no CM voltage fluctuations at the inputs of the transconductor 23. In practice, configuring CCO<<Cin may be beneficial for noise reasons. For example, a practical value of K>50 is desirable. For DM operation, VCO may be seen as AC ground, and the pair of capacitors CCO (without gain) may be virtually grounded.
In the transistor-level implementation shows in
Apart from functioning as the differential transconductor 23, the source-coupled transistor pairs M1-M2 and M3-M4 are also able to detect CM voltage fluctuations, and shift them to appear at the common source terminals of the two transistor pairs as VcmH and VcmL, respectively. The CM amplifier 27, which may be formed by formed by Cci, Ccf, Rcf and the transconductor AC, will perform CM signal amplification with a gain of −K=−2Cci/Ccf. As in the traditional way of designing an amplifier circuit for a neuromodulation device, the resistor Rcf can be made by a MOS pseudo-resistor. Thus, together with a small Ccf, a high-pass cut-off frequency below 1 Hz can be achieved within a tiny chip area. Besides, the transconductor AC only contributes CM noise that can be cancelled out in the differential mode. It can thus be designed in a compact and low-power fashion. Therefore, a large K can be achieved within a reasonable area.
In particular, for the results of
Notably, for the amplifier circuit 20 used in
The neuromodulation device 60 may further comprises at least one stimulator 62, which is configured to generate a stimulation signal 63, which can cause the neural modulation of the biological tissue. The stimulation signal 63 may be provided by a neural interface of the neuromodulation device 60 to the biological tissue. For instance, the neural interface may be a bi-directional neural interface, which is further configured to receive the one or more biological electrical signals 61 in response to the neural stimulation, and to provide them to the one or more amplifier circuits 20.
For example, as shown in
The shared CM amplifier 27 may improve the area per channel in the multichannel topology, since it can be shared among many recoding channels. This sharing is possible under the assumption that all recording electrodes (first set of electrodes 72) are placed in the nearby neighborhood and individually suffer from a comparable amount of CMI.
To achieve the same CM feedback gain (i.e., the same degree of CM suppression) for all N channels of the multichannel recording arrangement 80, only the one CM amplifier 27, including one transconductor Ac, but including N pairs of Cci/N (the same area occupied by one pair of Cci) and a pair of buffers can be used here. A pair of Cco is still used for each channel. This topology also offers weighted adjustment for each channel individually by adjusting the Cco value. This is useful, if the strength of the CMI appearing on each channel is known beforehand. The CM amplifier 27 may perform summing average of CMI and the required CEQ for each channel, and can be adjusted via the value of Cco according to (1) and the known CMI.
The multichannel recording arrangement 80 of
After the buffers 81 finish delivering a signal of one channel, further switches SR(reset switches) may be turned on for a short time, in order to erase memories stored on parasitic capacitances Cp, before the buffers 81 receive the signal again from the next consecutive channel. This resetting mechanism helps minimizing channel crosstalk. By sharing the buffers 81, a total power and area consumed and occupied by the buffers 81 will be divided by N when per-channel power and area are calculated.
An example embodiment of this disclosure is further a multichannel neuromodulation device, which comprises the multichannel recording arrangement 80 shown in
The multichannel scheme of
Sharing, for instance, two buffers 81 among the 16 outputs with negligible channel-to-channel crosstalk is also possible thanks to the reset switches SR.
In summary of this disclosure, an amplifier circuit 20, a neuromodulation device 60, and a recording arrangement 80 are provided. The amplifier circuit 20 is configured to suppress a CM voltage signal in the input voltage signal 22, and consequently to reduce CMI, while not degrading the input impedance.
| Number | Date | Country | Kind |
|---|---|---|---|
| 23193810.1 | Aug 2023 | EP | regional |
