CN216021085U - Analog front end AFE circuit and device for EEG signal acquisition - Google Patents

Abstract

The application discloses analog front end AFE circuit and device that EEG signal was gathered includes: an electrostatic discharge protection circuit ESD Protect; the buffer selection module is connected with the electrostatic discharge protection circuit ESDProtect; a differential low pass filter Diff LPF connected to the buffer selection module; an instrumentation amplifier INA connected to the differential low pass filter Diff LPF; the filter selection module is connected with the instrumentation amplifier INA; the first buffer is connected with the filter selection module; a first low pass filter LPF connected to the first buffer, and an analog-to-digital converter ADC connected to the first low pass filter LPF. Therefore, the AFE circuit has the advantages of simple link, low power consumption and few internal interference sources.

Description

Analog front end AFE circuit and device for EEG signal acquisition

Technical Field

The present application relates to the field of signal acquisition technologies, and in particular, to an analog front end AFE circuit and an analog front end AFE device for EEG signal acquisition.

Background

An analog front end AFE circuit in the conventional BCI EEG signal acquisition system generally adopts three schemes: 1. a DC-coupled single-ended mode; 2. a direct current coupled fully differential mode; 3. an ac coupling mode.

Disadvantages of AFE dc-coupled fully differential mode: 1. possess all single-ended link disadvantages; 2. A fully differential link requires 2 INA to generate differential signals. Disadvantages of AFE ac-coupled mode: 1. the link structure is relatively complex and the power consumption is high; 2. because of the high-pass filtering, the Delta (Delta) brainwaves near the direct current are lost; 3. input noise, CMRR (resistance mismatch), power frequency interference (resistance ground coupling) will be worse than DC mode; 4. overload recovery is slow.

Therefore, how to realize simple link, low power consumption and few internal interference sources is an urgent problem to be solved.

SUMMERY OF THE UTILITY MODEL

The application aims to provide an analog front end AFE circuit and an analog front end AFE device for EEG signal acquisition, which are simple in link, low in power consumption and few in internal interference sources.

In order to solve the above technical problem, the present application provides an analog front end AFE circuit for EEG signal acquisition, including:

an electrostatic discharge protection circuit ESD Protect; the buffer selection module is connected with the ESD protection circuit; a differential low pass filter Diff LPF connected to the buffer selection module;

an instrumentation amplifier INA connected to the differential low pass filter Diff LPF; the filter selection module is connected with the instrumentation amplifier INA;

the first buffer is connected with the filter selection module; a first low pass filter LPF connected to the first buffer, and an analog-to-digital converter ADC connected to the first low pass filter LPF.

Preferably, the buffer selection module includes a first switch matrix MUX, a second buffer, and a third buffer; the first output end of the first switch matrix is connected with the first input end of the differential low-pass filter through the second buffer, the second output end of the first switch matrix is connected with the second input end of the differential low-pass filter through the third buffer, the third output end of the first switch matrix is connected with the first input end of the differential low-pass filter, and the fourth output end of the first switch matrix is connected with the second input end of the differential low-pass filter.

Preferably, the filter selection module includes a second switch matrix MUX, a high pass filter HPF, and a second low pass filter LPF; the first output end of the second switch matrix is connected with the input end of the first buffer through a high-pass filter, the second output end of the second switch matrix is connected with the input end of the first buffer through a second low-pass filter, and the third output end of the second switch matrix is connected with the input end of the first buffer.

Preferably, the buffer selection module is configured to provide two options of adding a buffer and not adding a buffer for the analog front end AFE circuit; the filter selection module is used for carrying out high-pass filtering, low-pass filtering or no filtering through the second switch matrix.

Preferably, the analog front end AFE circuit further includes: and the test electrode and the reference electrode are connected with the input end of the electrostatic discharge protection circuit.

Preferably, the analog front end AFE circuit further includes: a resistor R1 and a resistor R2 which are connected with the instrumentation amplifier; a right leg drive circuit connected to the resistors R1 and R2; the right leg driving circuit is used for reducing common mode interference and power frequency interference.

The present application further provides a device for EEG signal acquisition, comprising:

n analog front end AFE circuits, 2N resistors, and 1 right leg driver circuit; n is a positive integer and is greater than or equal to 2;

for each instrumentation amplifier, each instrumentation amplifier has two R ports, each of which is connected to the right leg drive circuit through a resistor.

Preferably, the apparatus further comprises: and an electrode connected to the right leg drive circuit.

The application provides an analog front end AFE circuit and device that EEG signal was gathered, ESD protection circuit has been adopted, buffer, difference low pass filter, instrumentation amplifier INA has been chooseed for use to preamplifier, the filter selection module can carry out the filtering according to different needs and select the high pass, low pass or not filtering, and adopt anti-aliasing low pass filter and high accuracy ADC, so satisfy the low noise, low offset current, very high input impedance, it is simple to realize the link, the low power dissipation, the internal disturbance source is few.

Drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below, it is obvious that the drawings in the following description are only embodiments of the present application, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.

Fig. 1 is a schematic structural diagram of an analog front end AFE circuit for EEG signal acquisition according to an embodiment of the present disclosure;

fig. 2 is a schematic diagram of an analog front end AFE circuit for EEG signal acquisition according to an embodiment of the present disclosure;

fig. 3 is a schematic structural diagram of an EEG signal acquisition apparatus according to an embodiment of the present application.

Detailed Description

The core of the application is to provide an analog front end AFE circuit and an analog front end AFE device for EEG signal acquisition, so that the link is simple, the power consumption is low, and the internal interference sources are few.

In order to make the technical solutions of the present application better understood, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

Referring to fig. 1, fig. 1 is a schematic structural diagram of an analog front end AFE circuit for EEG signal acquisition according to an embodiment of the present application, where the analog front end AFE circuit includes:

an electrostatic discharge protection circuit ESD Protect 11; a buffer selection module 12 connected to an electrostatic discharge protection circuit ESD protection 11; a differential low pass filter Diff LPF13 coupled to the buffer selection block 12;

an instrumentation amplifier INA14 connected to a differential low pass filter Diff LPF 13; a filter selection module 15 connected to the instrumentation amplifier INA 14;

a first buffer16 coupled to the filter selection module 15; a first low pass filter LPF17 connected to the first buffer16, and an analog-to-digital converter ADC18 connected to the first low pass filter LPF 17.

The analog front end AFE circuit adopts an ESD protection circuit, a buffer, a differential low-pass filter, a preamplifier selects an instrumentation amplifier INA, a filter selection module can perform filtering selection high-pass according to different requirements, low-pass or no filtering is performed, an anti-aliasing low-pass filter and a high-precision ADC are adopted, so that low noise, low bias current and very high input impedance are met, a link is simple, power consumption is low, and internal interference sources are few.

In detail, the buffer selection module includes a first switch matrix MUX, a second buffer, and a third buffer; the first output end of the first switch matrix is connected with the first input end of the differential low-pass filter through the second buffer, the second output end of the first switch matrix is connected with the second input end of the differential low-pass filter through the third buffer, the third output end of the first switch matrix is connected with the first input end of the differential low-pass filter, and the fourth output end of the first switch matrix is connected with the second input end of the differential low-pass filter. The buffer selection module is used for providing two options of adding a buffer and not adding the buffer for the analog front end AFE circuit.

The filter selection module comprises a second switch matrix MUX, a high-pass filter HPF and a second low-pass filter LPF; the first output end of the second switch matrix is connected with the input end of the first buffer through a high-pass filter, the second output end of the second switch matrix is connected with the input end of the first buffer through a second low-pass filter, and the third output end of the second switch matrix is connected with the input end of the first buffer. The filter selection module is used for carrying out high-pass filtering, low-pass filtering or no filtering through the second switch matrix.

The first output end of the differential low-pass filter Diff LPF is connected with the positive input end of the instrumentation amplifier, and the second input end of the differential low-pass filter Diff LPF is connected with the inverting input section of the instrumentation amplifier. The analog front end AEF circuit further includes: and the test electrode and the reference electrode are connected with the input end of the electrostatic discharge protection circuit.

The method is based on the design of an analog front end IC (integrated circuit) for non-invasive EEG signal acquisition, acquires weak brain wave analog signals, filters and amplifies the signals, and then the signals enter an ADC (analog to digital converter) to be demodulated into digital signals. The EEG AFE can carefully handle static electricity, power frequency interference, RFI radio frequency interference, and EMI electromagnetic radiation in the environment. These sources of interference are avoided from affecting EEG data processing. Meanwhile, the actual severe electromagnetic environment, such as a medical environment, is also considered, and the device can also normally extract weak brain wave electric signals.

Referring to fig. 2, fig. 2 is a schematic diagram of an analog front end AFE circuit for EEG signal acquisition according to another embodiment of the present application, where the analog front end AEF circuit further includes: a resistor R1 and a resistor R2 connected to the instrumentation amplifier 14; and a right leg drive circuit 19 connected to the resistors R1 and R2. The right leg driving circuit 19 includes a buffer, an amplifier AMP, and a differential low pass filter Diff LPF, and is configured to reduce common mode interference and power frequency interference. The instrumentation amplifier 14 has two R ports, one of the R ports is connected to the buffer in the right leg driving circuit 19 through a resistor R1, the other R port is connected to the buffer in the right leg driving circuit 19 through a resistor R2, and the resistors R1 and R2 are connected in parallel.

In detail, in the AFE of the present application, an esd protection module is first required to reduce the damage of the external electromagnetic interference to the circuit device by contacting the electrodes. The function of the pre-Buffer in the circuit is that under the condition of small current, the circuit still has strong driving capability, and the design adds a switch matrix to provide two options of adding and not adding the Buffer for the circuit. The AFE circuit designs a Differential low pass filter (Differential LPF) to filter RFI. An instrumentation amplifier (INA) provides gain to the circuit and is connected to the right leg drive circuit through two parallel resistors, the instrumentation amplifier's primary function being to provide an extremely high common mode rejection ratio CMRR in the link. After the instrument amplification, high-pass filtering, low-pass filtering or no filtering can be carried out through a switch matrix according to different requirements. Then enters Buffer and a low pass filter, this time the low pass filter mainly performs ADC anti-aliasing filtering. Finally, the EEG signal is filtered and amplified by an analog-to-digital converter (ADC) which converts the analog signal to a digital signal. Because EEG signals are low in amplitude and are subject to electrode half-cell electrical +/-300mV bias voltage, and INA amplification is high, this requires high resolution for the ADC. In this case, the ADC is a 24-bit synchronous acquisition ADC.

The present application further provides a device for EEG signal acquisition, the device comprising:

n analog front end AFE circuits, 2N resistors, and 1 right leg driver circuit; n is a positive integer and is greater than or equal to 2; wherein, for each instrumentation amplifier, each instrumentation amplifier has two R ports, and each R port is connected with the right leg driving circuit through a resistor.

Further, the apparatus further comprises: and an electrode connected to the right leg drive circuit.

When N is equal to 8, 8channels are acquired, please refer to fig. 3, and fig. 3 is a schematic structural diagram of an EEG signal acquisition apparatus according to an embodiment of the present disclosure. The EEG signal acquisition device is designed to be an 8-channel synchronous acquisition circuit and simultaneously acquire EEG signals, and is connected with a right leg driving circuit (RLD) in parallel for reducing common mode interference and power frequency interference. Each EEG signal channel acquisition circuit is connected to the skin of the person by a test electrode and a reference electrode (the electrode locations are placed according to the international 10-20 system as required by the measurement).

Wherein, the differential low-pass filter pre-Buffer selects: AD8244, mainly because its bias current is smaller at 2pA and its input impedance is higher at 10 Tohm. Instrumentation amplifier (INA) selection: AD8422, because of its low voltage noise figure (maximum input voltage noise at 1kHz is 8nV/√ Hz) and high CMRR (> 80dB at 70 Hz). ADC selection: AD7768, because it is an 8channels, 24bit synchronous sampling, and a built-in SINC filter, is well suited for EEG data acquisition.

To sum up. EEG signals are very weak, perhaps between 10uV and 100uV, and are typically buried in power frequency common mode interference, Radio Frequency Interference (RFI), and electromagnetic interference (EMI) rejection. Therefore, to extract the EEG signal and filter the remaining noise requires the EEG AFE to have strong common mode rejection capability, low noise, low bias current, and high input impedance. Therefore, the AFE of the application adopts an ESD protection circuit, a buffer drive, a differential low-pass filter, a preamplifier adopts an instrumentation amplifier (INA), a multi-selection filter circuit can perform filtering selection (high-pass, low-pass or no filtering) according to different requirements, and an anti-aliasing low-pass filter and a high-precision ADC meet the performance requirements. According to the extraction characteristics of EEG signals, the AFE in a single-ended mode is designed, the power consumption is low, the link is simple, the number of devices is small, the number of internal interference sources is small, the link input noise is small, and the CMRR parameter is good.

The analog front end AFE circuit and the apparatus for EEG signal acquisition provided by the present application are described in detail above. The principles and embodiments of the present application are explained herein using specific examples, which are provided only to help understand the method and the core idea of the present application. It should be noted that, for those skilled in the art, it is possible to make several improvements and modifications to the present application without departing from the principle of the present application, and such improvements and modifications also fall within the scope of the claims of the present application.

Claims (8)

1. An Analog Front End (AFE) circuit for EEG signal acquisition, comprising:

an electrostatic discharge protection circuit ESD Protect; the buffer selection module is connected with the ESD protection circuit; a differential low pass filter Diff LPF connected to the buffer selection module;

an instrumentation amplifier INA connected to the differential low pass filter Diff LPF; the filter selection module is connected with the instrumentation amplifier INA;

the first buffer is connected with the filter selection module; a first low pass filter LPF connected to the first buffer, and an analog-to-digital converter ADC connected to the first low pass filter LPF.

2. The analog front end AFE circuit of claim 1, wherein the buffer selection module comprises a first switch matrix MUX, a second buffer, a third buffer; the first output end of the first switch matrix is connected with the first input end of the differential low-pass filter through the second buffer, the second output end of the first switch matrix is connected with the second input end of the differential low-pass filter through the third buffer, the third output end of the first switch matrix is connected with the first input end of the differential low-pass filter, and the fourth output end of the first switch matrix is connected with the second input end of the differential low-pass filter.

3. The analog front end AFE circuit of claim 1, wherein the filter selection block comprises a second switch matrix MUX, a high pass filter HPF, a second low pass filter LPF; the first output end of the second switch matrix is connected with the input end of the first buffer through a high-pass filter, the second output end of the second switch matrix is connected with the input end of the first buffer through a second low-pass filter, and the third output end of the second switch matrix is connected with the input end of the first buffer.

4. The analog front end AFE circuit of claim 1 wherein the buffer selection module is to provide both an add buffer and an add not buffer option for the analog front end AFE circuit; the filter selection module is used for carrying out high-pass filtering, low-pass filtering or no filtering through the second switch matrix.

5. The analog front end AFE circuit of claim 1, further comprising: and the test electrode and the reference electrode are connected with the input end of the electrostatic discharge protection circuit.

6. The analog front end AFE circuit of claim 1, further comprising: a resistor R1 and a resistor R2 which are connected with the instrumentation amplifier; a right leg drive circuit connected to the resistors R1 and R2; the right leg driving circuit is used for reducing common mode interference and power frequency interference.

7. An apparatus for EEG signal acquisition, comprising:

n analog front end AFE circuits of any of claims 1 to 5, 2N resistors, and 1 right leg driver circuit; n is a positive integer and is greater than or equal to 2;

for each instrumentation amplifier, each instrumentation amplifier has two R ports, each of which is connected to the right leg drive circuit through a resistor.

8. The analog front end AFE circuit of claim 7, further comprising: and an electrode connected to the right leg drive circuit.

Images