CN113208606A - Analog front end AFE circuit for EEG signal acquisition - Google Patents
Analog front end AFE circuit for EEG signal acquisition Download PDFInfo
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- CN113208606A CN113208606A CN202110407866.4A CN202110407866A CN113208606A CN 113208606 A CN113208606 A CN 113208606A CN 202110407866 A CN202110407866 A CN 202110407866A CN 113208606 A CN113208606 A CN 113208606A
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Abstract
The invention discloses an analog front end AFE circuit for EEG signal acquisition, which comprises: an instrumentation amplifier; the instrument amplifier is an instrument amplifier with differential output; the signal buffer is connected with the instrument amplifier; a differential low pass filter coupled to the signal buffer; and the analog-to-digital converter is connected with the differential low-pass filter. Therefore, the analog front end AFE circuit provides a brand-new fully-differential link architecture, and improves the signal-to-noise ratio and the anti-interference capability.
Description
Technical Field
The invention relates to the technical field of circuits, in particular to an analog front end AFE circuit for EEG signal acquisition.
Background
EEG signals represent the electroencephalogram, which is a general reflection of the electrophysiological activity of brain neurons on the surface of the cerebral cortex or scalp. The electroencephalogram signals contain a large amount of physiological and disease information, and are widely applied to brain activity analysis and disease diagnosis. However, because the EEG signal has low amplitude and strong randomness and nonlinearity, it is very susceptible to other signals during the acquisition process, which increases the difficulty of subsequent analysis.
Because the electroencephalogram signals are acquired by transmitting synchronous discharge of cerebral cortex neuron groups to the electrodes placed on the scalp through a plurality of layers of tissues such as cortex, cerebrospinal fluid, dura mater, skull, scalp and the like, the electroencephalogram signals are very easy to be polluted, and the brain function information hidden in the EEG is probably covered by noise, even wrong conclusions are obtained. Common EEG signal noise can be classified as non-physiological and physiological. In physiological noise, such as: breathing, heartbeat. Non-physiological noise, such as: power frequency, mobile phone radio frequency, etc.
Existing EEG data acquisition schemes are: the AFE front end adopts an instrumentation amplifier (INA) differential input and single-ended output. Then single end is amplified and filtered, and data is sent to an analog-to-digital converter (ADC) for sampling. Referring to fig. 1, fig. 1 is a schematic diagram of an analog front end AFE structure based on an EEG signal in the prior art, i.e., an EEG AFE, where reference numeral 6 denotes a single-ended signal. The instrumentation amplifier is a standard three-operational amplifier architecture, and in order to meet the requirement of common mode rejection ratio CMRR, a subtracter is used for differential signals inside the instrumentation amplifier, so that the output is a single-ended signal. Meanwhile, the single-ended signal is filtered, amplified, buffered and ADC sampled in a rear link. The EEG signal is single ended, and is less robust to interference than differential signals, regardless of accuracy, signal to noise ratio, and the like. However, the existing instrumentation amplifier is single-ended output, and cannot meet the requirement of full difference. The excellent performance of the EEG fully differential link is important when pursuing high performance EEG data acquisition signals.
Therefore, how to provide a brand-new fully-differential link architecture and improve the signal-to-noise ratio and the anti-interference capability is an urgent problem to be solved.
Disclosure of Invention
The invention aims to provide an analog front end AFE circuit for EEG signal acquisition, which realizes the provision of a brand-new fully-differential link architecture and improves the signal-to-noise ratio and the anti-interference capability.
To solve the above technical problem, the present invention provides an analog front end AFE circuit for EEG signal acquisition, comprising:
an instrumentation amplifier; the instrument amplifier is an instrument amplifier with differential output;
the signal buffer is connected with the instrument amplifier;
a differential low pass filter coupled to the signal buffer;
and the analog-to-digital converter is connected with the differential low-pass filter.
Preferably, the analog front end AFE circuit further includes:
the input protection device is connected with the first input end and the second input end of the instrument amplifier;
and the digital processor is connected with the analog-to-digital converter.
Preferably, the first output end and the second output end of the instrumentation amplifier are respectively connected with the first input end and the second input end of the signal buffer;
a first output end and a second output end of the signal buffer are respectively connected with a first input end and a second input end of the differential low-pass filter;
and a first output end and a second output end of the differential low-pass filter are respectively connected with a first input end and a second input end of the analog-to-digital converter.
Preferably, the instrumentation amplifier outputs a differential signal, and two three operational amplifier instrumentation amplifiers are cross-connected, including a first three operational amplifier instrumentation amplifier, a second three operational amplifier instrumentation amplifier, and a gain resistor R0.
Preferably, the first three operational amplifier instrumentation amplifier comprises operational amplifiers A1, A2, A3 and resistors R1, R2, R3, R4, R5, R11, and the second three operational amplifier instrumentation amplifier comprises operational amplifiers A4, A5, A6 and resistors R6, R7, R8, R9, R10, R12.
Preferably, the non-inverting input terminal of the operational amplifier a1 and the non-inverting input terminal of the operational amplifier a2 are both connected to the first input terminal of the differential output instrumentation amplifier, the output terminal of the operational amplifier a1 is connected to the inverting input terminal of the operational amplifier a1 through the resistor R1, and the output terminal of the operational amplifier a2 is connected to the inverting input terminal of the operational amplifier a2 through the resistor R2; the inverting input end of the operational amplifier A3 is divided into two paths, one path is connected with the output end of A1 through R3, the other path is connected with one end of R5, and the other end of R5 and the output end of A3 are both connected with the first output end of the differential output instrument amplifier; the non-inverting input end of the operational amplifier A3 is divided into two paths, one path is connected with the output end of A2 through R4, and the other path is grounded through R11.
Preferably, the non-inverting input terminal of the operational amplifier a4 and the non-inverting input terminal of the operational amplifier a5 are both connected to the second input terminal of the differential output instrumentation amplifier, the output terminal of the operational amplifier a4 is connected to the inverting input terminal of the operational amplifier a4 through the resistor R6, and the output terminal of the operational amplifier a5 is connected to the inverting input terminal of the operational amplifier a5 through the resistor R7; the inverting input end of the operational amplifier A6 is divided into two paths, one path is connected with the output end of A4 through R8, the other path is grounded through R12, the non-inverting input end of the operational amplifier A6 is divided into two paths, one path is connected with the output end of A5 through R9, the other path is connected with one end of R10, and the other end of R10 and the output end of A6 are both connected with the second output end of the differential output instrumentation amplifier; the inverting input terminal of a5 and the inverting input terminal of a1 are connected through a gain resistor R0.
The analog front-end AFE circuit for EEG signal acquisition provided by the invention redesigns the traditional EEG AFE single-ended link, and reforms the single-ended link into a differential link, the design of the differential link is different from that of the single-ended link, the filter and the buffer link both need to adopt a differential mode, the filter adopts a differential low-pass filter, and the signal buffer adopts a dual-channel operational amplifier circuit, so that a brand-new fully-differential link architecture is realized.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, 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 diagram of a prior art EEG signal based analog front end AFE architecture;
fig. 2 is a schematic diagram of an analog front end AFE circuit for EEG signal acquisition according to an embodiment of the present invention;
fig. 3 is a schematic structural diagram of an instrumentation amplifier with differential output according to an embodiment of the present invention.
Detailed Description
The core of the invention is to provide an analog front end AFE circuit for EEG signal acquisition so as to provide a brand-new fully-differential link architecture and improve the signal-to-noise ratio and the anti-interference capability.
In order to make the technical solutions of the present invention better understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, 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 invention.
Fig. 2 is a schematic structural diagram of an analog front end AFE circuit for EEG signal acquisition according to an embodiment of the present invention, the analog front end AFE circuit includes:
an instrumentation amplifier INA; the instrumentation amplifier INA is an instrumentation amplifier with differential output;
a signal BUFFER connected to the instrumentation amplifier INA;
a differential low-pass FILTER connected to the signal BUFFER;
an analog-to-digital converter ADC connected to a differential low-pass FILTER.
Further, the method also comprises the following steps:
the Input protection device is connected with the first Input end and the second Input end of the instrumentation amplifier INA;
and a Digital processor Digital Processing connected with the analog-to-Digital converter ADC.
In fig. 2, reference numeral 1 denotes an instrumentation amplifier INA, reference numeral 2 denotes a signal BUFFER, reference numeral 3 denotes a differential signal, reference numeral 4 denotes a differential low-pass FILTER, and reference numeral 5 denotes an analog-to-digital converter ADC. The electrodes are represented by electrodes, the number of the Input production of the protection devices is multiple, the protection devices are sequentially connected, and the output end of the first Input production and the output end of the last Input production are respectively connected with the first Input end and the second Input end of the instrumentation amplifier INA.
In detail, a first output end and a second output end of the instrument amplifier are respectively connected with a first input end and a second input end of the signal buffer; the first output end and the second output end of the signal buffer are respectively connected with the first input end and the second input end of the differential low-pass filter; the first output end and the second output end of the differential low-pass filter are respectively connected with the first input end and the second input end of the analog-to-digital converter.
Comparing the two schemes in fig. 1 and fig. 2, it can be seen that the differential link is to fully utilize the characteristics of strong interference rejection and high signal-to-noise ratio of the differential signal, so that the traditional EEG AFE single-ended link is redesigned, and the single-ended link is modified into the differential link. The design of the differential link is different from that of a single-ended link, a filter and a buffer link both need to adopt a differential mode, the filter adopts a differential low-pass filter, and a signal buffer is realized by adopting a double-channel operational amplifier circuit. The instrumentation amplifier INA is the circuit at the top of the link, determines many key parameters of the link, such as input noise, common mode rejection ratio CMRR, bias current, offset voltage, etc., and the instrumentation amplifier INA on the market is single-ended output, so how to design the differential output instrumentation amplifier becomes the most important work.
In detail, the instrumentation amplifier outputs a differential signal, and two three operational amplifier instrumentation amplifiers are cross-connected, including a first three operational amplifier instrumentation amplifier, a second three operational amplifier instrumentation amplifier, and a gain resistor R0. Referring to fig. 3, fig. 3 is a schematic structural diagram of an instrumentation amplifier with differential output according to an embodiment of the present invention, in order to enable the instrumentation amplifier to output differential signals, two instrumentation amplifiers are cross-connected, and Vout _ a and Vout _ B in fig. 3 output just full differential signals. This new circuit provides a fully differential output with fine gain or attenuation using a single gain resistor. And has the advantage that the link does not use a matching resistor, so the performance of the instrumentation amplifier is not affected. The output can be adjusted and the common mode voltage can be controlled as required by a new special design mode of connecting the two reference pins together. In fig. 3, reference 7 denotes a first three op-amp instrumentation amplifier, reference 8 denotes a second three op-amp instrumentation amplifier, reference 9 denotes the instrumentation amplifier reference, i.e., the circuit "ground", the zero point, and reference 10 denotes the gain resistance, i.e., R0.
The first three operational amplifier instrumentation amplifiers comprise operational amplifiers A1, A2 and A3 and resistors R1, R2, R3, R4, R5 and R11, and the second three operational amplifier instrumentation amplifiers comprise operational amplifiers A4, A5 and A6 and resistors R6, R7, R8, R9, R10 and R12.
The non-inverting input end of the operational amplifier A1 and the non-inverting input end of the operational amplifier A2 are both connected with the first input end of the differential output instrumentation amplifier, the output end of the operational amplifier A1 is connected with the inverting input end of the operational amplifier A1 through a resistor R1, and the output end of the operational amplifier A2 is connected with the inverting input end of the operational amplifier A2 through R2; the inverting input end of the operational amplifier A3 is divided into two paths, one path is connected with the output end of A1 through R3, the other path is connected with one end of R5, and the other end of R5 and the output end of A3 are both connected with the first output end of the differential output instrument amplifier; the non-inverting input end of the operational amplifier A3 is divided into two paths, one path is connected with the output end of A2 through R4, and the other path is grounded through R11.
The non-inverting input end of the operational amplifier A4 and the non-inverting input end of the operational amplifier A5 are both connected with the second input end of the differential output instrumentation amplifier, the output end of the operational amplifier A4 is connected with the inverting input end of the A4 through a resistor R6, and the output end of the operational amplifier A5 is connected with the inverting input end of the A5 through R7; the inverting input end of the operational amplifier A6 is divided into two paths, one path is connected with the output end of A4 through R8, the other path is grounded through R12, the non-inverting input end of the operational amplifier A6 is divided into two paths, one path is connected with the output end of A5 through R9, the other path is connected with one end of R10, and the other end of R10 and the output end of A6 are both connected with the second output end of the differential output instrumentation amplifier; the inverting input terminal of a5 and the inverting input terminal of a1 are connected through a gain resistor R0.
The invention designs an AFE circuit for EEG signal acquisition, which adopts a brand-new fully-differential link to realize EEG weak signal acquisition, provides an AFE circuit for EEG signal acquisition based on the fully-differential link, redesigns a traditional EEG AFE single-ended link, and reforms the single-ended link into a differential link, wherein the differential link is different from the single-ended link in design, a filter and a buffer link both need to adopt a differential mode, the filter adopts a differential low-pass filter, the buffer adopts a double-channel operational amplifier, and a signal buffer has a double-channel operational amplifier.
The analog front end AFE circuit for EEG signal acquisition provided by the present invention is described in detail above. The principles and embodiments of the present invention are explained herein using specific examples, which are presented only to assist in understanding the method and its core concepts. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention.
Claims (7)
1. An Analog Front End (AFE) circuit for EEG signal acquisition, comprising:
an instrumentation amplifier; the instrument amplifier is an instrument amplifier with differential output;
the signal buffer is connected with the instrument amplifier;
a differential low pass filter coupled to the signal buffer;
and the analog-to-digital converter is connected with the differential low-pass filter.
2. The analog front end AFE circuit of claim 1, further comprising:
the input protection device is connected with the first input end and the second input end of the instrument amplifier;
and the digital processor is connected with the analog-to-digital converter.
3. An analog front end AFE circuit according to claim 1 wherein first and second outputs of the instrumentation amplifier are connected to first and second inputs, respectively, of the signal buffer;
a first output end and a second output end of the signal buffer are respectively connected with a first input end and a second input end of the differential low-pass filter;
and a first output end and a second output end of the differential low-pass filter are respectively connected with a first input end and a second input end of the analog-to-digital converter.
4. An analog front end AFE circuit according to claim 1 wherein the instrumentation amplifier outputs a differential signal using two three op-amp cross-connects including a first three op-amp instrumentation amplifier, a second three op-amp instrumentation amplifier, and a gain resistor R0.
5. An analog front end AFE circuit as claimed in claim 4 in which the first three op-amp instrumentation amplifiers comprise operational amplifiers a1, a2, A3 and resistors R1, R2, R3, R4, R5, R11 and the second three op-amp instrumentation amplifiers comprise operational amplifiers a4, a5, A6 and resistors R6, R7, R8, R9, R10, R12.
6. An analog front end AFE circuit as claimed in claim 5, wherein the non-inverting input of operational amplifier A1 and the non-inverting input of operational amplifier A2 are both connected to the first input of the differential output instrumentation amplifier, the output of operational amplifier A1 is connected to the inverting input of A1 via resistor R1, and the output of operational amplifier A2 is connected to the inverting input of A2 via R2; the inverting input end of the operational amplifier A3 is divided into two paths, one path is connected with the output end of A1 through R3, the other path is connected with one end of R5, and the other end of R5 and the output end of A3 are both connected with the first output end of the differential output instrument amplifier; the non-inverting input end of the operational amplifier A3 is divided into two paths, one path is connected with the output end of A2 through R4, and the other path is grounded through R11.
7. An analog front end AFE circuit as claimed in claim 6, wherein the non-inverting input of operational amplifier A4 and the non-inverting input of operational amplifier A5 are both connected to the second input of the differential output instrumentation amplifier, the output of operational amplifier A4 is connected to the inverting input of A4 via resistor R6, and the output of operational amplifier A5 is connected to the inverting input of A5 via R7; the inverting input end of the operational amplifier A6 is divided into two paths, one path is connected with the output end of A4 through R8, the other path is grounded through R12, the non-inverting input end of the operational amplifier A6 is divided into two paths, one path is connected with the output end of A5 through R9, the other path is connected with one end of R10, and the other end of R10 and the output end of A6 are both connected with the second output end of the differential output instrumentation amplifier; the inverting input terminal of a5 and the inverting input terminal of a1 are connected through a gain resistor R0.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN115399750A (en) * | 2022-07-25 | 2022-11-29 | 知心健(南京)科技有限公司 | Method for measuring respiratory impedance |
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| CN115399750A (en) * | 2022-07-25 | 2022-11-29 | 知心健(南京)科技有限公司 | Method for measuring respiratory impedance |
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