A method for eliminating direct current offset between electrodes of an electroencephalogram acquisition device by using digital-analog hybrid DSL technology

Abstract

The application discloses a method for eliminating direct current offset between electrodes of an electroencephalogram acquisition device by using digital-analog hybrid DSL technology, and relates to electroencephalogram signal processing. The method comprises the following steps: transmitting an electroencephalogram acquisition input signal to a signal amplification module for amplification processing to obtain a first amplified electroencephalogram signal, and processing the first amplified electroencephalogram signal through an analog direct current servo loop module to obtain a second analog direct current component; then, transmitting the electroencephalogram acquisition input signal to a digital direct current servo loop module to obtain a first digital direct current component; then, converting the first digital direct current component and the second analog direct current component into alternating current through a capacitor and a chopping modulation module to offset input end alternating current; then, transmitting the first amplified electroencephalogram signal to a programmable gain amplification module for secondary amplification processing to obtain a second amplified electroencephalogram signal, inputting the second amplified electroencephalogram signal to an anti-aliasing filter, and inputting the second amplified electroencephalogram signal to a digital processing module after analog signal conversion for processing. The application shortens the time for EDO offset at the input end, and the sampling rate of an analog-to-digital converter in the digital servo loop is very low, so that the power consumption of the digital servo loop is very small, thereby effectively solving the problems of difficult realization of a high EDO suppression range and low input reference noise, and the problems of a too large time constant of an integrator in a traditional analog direct current servo loop and a too long EDO offset time.

Description

Technical Field

[0001] This invention relates to the field of electroencephalogram (EEG) signal processing, and more specifically to a method for eliminating DC offset between electrodes in an EEG acquisition device using mixed analog-digital (DSL) technology. Background Technology

[0002] Brain-computer interfaces (BCIs) are a cutting-edge technology that allows humans to communicate with computers or other external devices through methods such as electrical signal acquisition, feature extraction, feature classification, and external control. The aim is to recreate the brain's operating mechanisms and enable control of external devices, achieving direct communication between humans and machines. This technology holds immense potential in fields such as medicine, assistive technology, and virtual reality.

[0003] Brain-computer interface systems for mobile applications need to record brain potential signals, particularly electroencephalography (EEG), in a non-invasive and comfortable manner while maintaining signal quality. Secondly, to achieve reliable signal detection, high electrode DC bias (EDO) of up to ±300mV must be rejected. EDO arises from the difference in half-cell potential between the electrode and the electrolyte; the half-cell potential of gel electrodes can reach tens of millivolts. EDO is a critical consideration in brain potential amplifier design because it can saturate the amplifier chain and distort the signal. Although often considered a DC bias, EDO is actually not constant and varies over time due to electrode displacement. To address this, brain potential amplifiers must possess AC coupling characteristics to eliminate EDO. Simultaneously, they are susceptible to low-frequency noise, particularly the 1 / f noise present in CMOS amplifiers. Therefore, the requirements for low input reference noise and high EDO suppression range also need to be addressed through low power consumption.

[0004] One possible solution is to use a capacitor-coupled instrumentation amplifier (CCIA), which achieves this by placing a capacitor at the input, such as... Figure 2 As shown. Since the amplification factor and high-pass corner frequency are respectively determined by C... F The ratio of Cin to R F C F The time constant of the input capacitor dictates that very large capacitors are typically required to achieve high gain and extremely low cutoff frequency. This is impractical in multichannel recording applications due to the need for a large silicon area. Besides area loss, capacitor mismatch makes the CCIA sensitive to large common-mode interference. A common circuit design technique to address this problem is to use a chopper-stabilized brain potential amplifier. This technique has been widely used in biosensor analog front-ends because it offers 1 / f noise suppression, low offset, continuous-time operation, and low-noise folding compared to self-zeroing techniques. To mitigate capacitor mismatch, a chopper is typically placed before the input capacitor and another chopper at the amplifier's output, such as... Figure 3As shown. In this way, the capacitor mismatch is converted into differential-mode common-mode interference, which is then converted to a higher frequency. However, adding a chopping function has the following disadvantages. First, the presence of a switched capacitor at the input affects the input impedance; the CCIA's input impedance is approximately 1 / 2f. chop Cin, where f chop The chopper represents the chopping frequency, and Cin represents the input capacitance. Secondly, by positioning the chopper before the input capacitor, the EDO is shifted to a higher frequency band, causing the input capacitor Cin to lose its ability to isolate the EDO. Therefore, additional circuitry is needed to suppress the EDO.

[0005] To address the issue of EDO at the input of a chopper amplifier causing saturation, such as... Figure 4 As shown, the first problem with traditional DSL is that the 1 / f noise of the integrator cannot be avoided. EDO，MAX Both noise and input reference noise are proportional to the capacitance Chp, making it difficult to achieve a high EDO suppression range and low input reference noise. The second problem is that the integrator time constant is very large, resulting in excessively long feedback times when the EDO is large. Therefore, it is difficult to achieve a high EDO suppression range, low input reference noise, and fast feedback speed. Summary of the Invention

[0006] In view of this, the purpose of this invention is to provide a method for eliminating DC offset between electrodes in EEG acquisition devices using mixed-signal DSL technology, aiming to solve the aforementioned problems. Compared with traditional analog DC servo circuits, this invention adopts a mixed-signal dual-circuit approach, shortening the EDO cancellation time at the input end. Furthermore, the sampling rate of the analog-to-digital converter in the digital servo circuit is very low, resulting in very low power consumption. This effectively solves the problems of difficulty in achieving high EDO suppression range and low input reference noise, as well as the problems of excessively large integrator time constants and excessively long EDO cancellation times in traditional analog DC servo circuits. It is suitable for wearable EEG acquisition systems.

[0007] To achieve the above objectives, the present invention provides a method for eliminating DC offset between electrodes in an EEG acquisition device using mixed-signal DSL technology, comprising the following steps:

[0008] Step S1: The first input signal acquired by the wearable extracranial microelectrode EEG detection device is transmitted to the signal amplification module through the input terminals Vinp and Vinn of the front-end acquisition chip. The signal amplification module amplifies the EEG signal in the first input signal to obtain the initially amplified first amplified EEG signal. The first input signal is also transmitted to the digital DC servo circuit module through the input terminals Vinp and Vinn of the front-end acquisition chip. The digital DC servo circuit processes the EEG signal in the first input signal to obtain the first digital DC component of the EEG signal at the Vinp and Vinn terminals. The first amplified EEG signal is transmitted to the analog DC servo circuit module, which processes the first amplified EEG signal to obtain the corresponding second analog DC component. The first digital DC component and the second analog DC component are converted into alternating current through a capacitor and chopper modulation module and connected to the input terminal of the signal amplification module in opposite directions.

[0009] Step S2: The first amplified EEG signal is transmitted to the programmable gain amplifier module. The programmable gain amplifier module performs secondary amplification on the first amplified EEG signal. The high-pass characteristics provided by the feedback capacitor and feedback resistor are used to filter out the residual DC offset voltage after the mixed-signal DC servo circuit processing, so as to obtain an amplified second amplified EEG signal with consistent DC components.

[0010] Step S3: Input the second EEG signal with the same DC component to the anti-aliasing filter to filter out various harmonic noises, thereby leaving the acquired third EEG signal;

[0011] Step S4: Input the filtered third EEG signal into an analog-to-digital converter to convert the analog signal into a fourth digital EEG signal;

[0012] Step S5: Input the converted fourth EEG digital signal into the digital processing module for processing.

[0013] In one specific embodiment, the signal amplification module includes a chopper modulation unit, an input capacitor Cin1, a fixed gain amplification unit, and a chopper demodulation unit. Step S1 specifically includes the following sub-steps:

[0014] Step S11: The electrodes worn outside the skull, equipped with an EEG signal acquisition device, pass the acquired input signal through a buffer to ensure that the amplification path is consistent with the non-ideal factors in the digital servo circuit, in order to offset the offset voltage generated by the buffer in the digital DC servo circuit module.

[0015] Step S12: The signal after passing through the buffer is transmitted to the signal amplification module through the input terminal of the signal amplification path. The chopper modulation unit in the signal amplification module performs chopper modulation on the EEG signal in the input signal to avoid the noise in the low frequency part of the amplifier and outputs the chopper-modulated EEG signal.

[0016] Step S13: The chopper-modulated EEG signal is amplified by the input capacitor Cin1 and the fixed gain amplification unit to obtain the initially amplified modulated EEG signal.

[0017] Step S14: The initially amplified modulated EEG signal is transmitted to the chopper demodulation unit for signal demodulation, and the signal is demodulated to the original signal frequency band to obtain the initially amplified first amplified EEG signal.

[0018] In one specific embodiment, the digital DC servo loop module includes an analog-to-digital converter (ADC), a resistive digital-to-analog converter (R-DAC), a buffer, a chopper modulation unit, and an input capacitor Cin. The first input signal is transmitted to the digital DC servo loop module via the input terminals Vinp and Vinn of the front-end acquisition chip. The ADC in the digital DC servo loop module samples, quantizes, and encodes the EEG signal in the input signal to obtain digital codes for the DC components of the EEG signals at the Vinp and Vinn terminals, respectively. The digital codes for the DC components of the EEG signals at the Vinp and Vinn terminals are converted from digital signals to analog signals by the resistive digital-to-analog converter (R-DAC) to obtain the DC level of the original EEG signal. The DC level of the original EEG signal is boosted by the buffer and output as the first digital DC component.

[0019] In one specific embodiment, the analog DC servo loop module includes an integrator unit, a chopper modulation unit, and a capacitor Chp; wherein, the first amplifier EEG signal is transmitted to the analog DC servo loop module, and the integrator unit in the analog DC servo loop module filters out the AC component in the first amplifier EEG signal to obtain the DC level of the first amplifier EEG signal, which is the second analog DC component.

[0020] In one specific embodiment, the fixed-gain amplification unit includes a fixed-gain amplifier, two fixed-feedback capacitors, and two fixed-feedback resistors. The two fixed-feedback capacitors are connected to the two ends of the fixed-gain amplifier, and the two fixed-feedback resistors are connected to the outer sides of each of the two fixed-feedback capacitors. The fixed-gain amplifier is defined as follows:

[0021] In one specific embodiment, the programmable gain amplification module includes an input capacitor Cin2 and a variable gain amplification unit. Step S2 specifically includes the following sub-steps: transmitting the first amplified EEG signal to the input capacitor Cin2 and the variable gain amplification unit, and amplifying the signal by adjusting the variable gain to obtain the amplified second amplified EEG signal.

[0022] In one specific embodiment, the variable gain amplification unit includes a variable gain amplifier, two variable feedback capacitors for single-pole double-throw switches, and two feedback resistors. The two ends of the variable gain amplifier are connected to the two variable feedback capacitors for the single-pole double-throw switches, and the two feedback resistors are respectively connected to the outside of the two variable feedback capacitors for the single-pole double-throw switches.

[0023] In one specific embodiment, the anti-aliasing filter filters out various harmonic noises, thereby leaving the acquired third EEG signal.

[0024] In one specific embodiment, the analog-to-digital converter inputs the filtered third EEG signal to the analog-to-digital converter module, converting the amplitude- and time-continuous analog signal into a discrete digital signal.

[0025] In a second aspect of the invention, a system for eliminating DC offset between electrodes in an electroencephalogram (EEG) acquisition device using mixed-signal DSL technology is provided, comprising:

[0026] Signal amplification module: used to amplify the EEG signal in the input signal to obtain an amplified first amplified EEG signal; wherein, the signal amplification module includes a chopper modulation unit, an input capacitor Cin1, a fixed gain amplification unit, and a chopper demodulation unit; the chopper modulation unit is used to chopper modulate the EEG signal to avoid noise in the low-frequency part of the amplifier and output the chopper modulated EEG signal; the input capacitor Cin1 and the fixed gain amplification unit are used to amplify the chopper modulated EEG signal to obtain an initially amplified modulated EEG signal; the chopper demodulation unit is used to demodulate the modulated EEG signal to the original signal frequency band to obtain the first amplified EEG signal;

[0027] A digital DC servo loop module is used to process the EEG signal in the input signal to obtain the first digital DC component of the Vinp and Vinn terminal EEG signals. The digital DC servo loop module includes an analog-to-digital converter (ADC), a resistive digital-to-analog converter (R-DAC), a buffer, a chopper modulation unit, and an input capacitor Cin. The ADC samples, quantizes, and encodes the EEG signal in the input signal to obtain digital codes for the DC components of the Vinp and Vinn terminal EEG signals. The R-DAC converts the digital codes of the Vinp and Vinn terminal EEG signal DC components into analog signals to obtain the DC level of the original EEG signal, which is the first digital DC component. The buffer enhances the driving capability of the DC level of the original EEG signal. The first digital DC component is converted into alternating current by the capacitor and the chopper modulation module and connected to the input terminal of the signal amplification module in opposite directions.

[0028] Analog DC servo circuit module: processes the initially amplified first EEG signal to obtain the corresponding second analog DC component; wherein, the analog DC servo circuit module includes an integrator unit, a chopper modulation unit, and a capacitor Chp; the integrator unit filters out the AC component in the EEG signal, and the DC level of the first amplified EEG signal is the second analog DC component; wherein, the second analog DC component is converted into AC current by the capacitor and the chopper modulation module and connected to the input terminal of the signal amplification module in opposite directions;

[0029] Programmable gain amplifier module: used to perform secondary amplification of the first amplified EEG signal in the input signal to obtain an amplified EEG signal. The high-pass characteristic provided by the feedback capacitor and feedback resistor is used to filter out the residual DC offset voltage after the mixed-signal DC servo circuit processing to obtain an amplified second amplified EEG signal with consistent DC components. The programmable gain amplifier module includes an input capacitor Cin2 and a variable gain amplifier unit. The input capacitor Cin2 and the variable gain amplifier unit are used to adjust the variable gain to amplify the second amplified EEG signal.

[0030] Anti-aliasing filter: filters out various harmonic noises, thus leaving the acquired third EEG signal;

[0031] Analog-to-digital converter: converts analog signals with continuous amplitude and time into discrete fourth EEG digital signals;

[0032] Digital processor: used to process the decoded fourth EEG digital signal to obtain the final EEG signal.

[0033] Compared with existing technologies, this invention has the following advantages: First, the acquired input signal is transmitted to a signal amplification module via the input terminal of a front-end acquisition chip. The signal amplification module amplifies the EEG signal in the input signal to obtain an initially amplified EEG signal. Then, simultaneously, the acquired input signal is transmitted to a digital DC servo circuit module via the input terminal of the front-end acquisition chip. The digital DC servo circuit processes the EEG signal in the input signal to obtain the DC component of the input EEG signal. Afterward, the initially amplified EEG signal is transmitted to an analog DC servo circuit module, which processes the initially amplified EEG signal... The signal is processed to obtain the corresponding DC component. This DC component is then converted into AC current by a capacitor and a chopper modulation module to cancel the input AC current. The amplified EEG signal is then transmitted to a programmable gain amplifier module, which performs secondary amplification. The amplified EEG signal with the same DC component is then input to an anti-aliasing filter to remove various harmonic noises, leaving only the acquired EEG signal. The filtered EEG signal is then input to an analog-to-digital converter (ADC) to convert the analog signal into a digital signal. Finally, the converted digital EEG signal is input to a digital processing module for processing. In chopper amplifiers using dry contact electrodes, EDO (Electronic Denoising) as high as ±300mV can occur at the chopper amplifier input. Traditional methods employ analog DC servo loops to avoid chopper amplifier saturation caused by EDO. The principle of the DC servo loop is that the analog integrator samples the DC component at the output of the OTA (Over-The-Air) and cancels it at the input of the OTA. A problem with traditional DSLs is that the 1 / f noise of the integrator cannot be avoided. EDO，MAX Both noise and capacitance (Chp) are proportional, making it difficult to achieve a high EDO suppression range and low input reference noise. Compared to traditional analog DC servo circuits, this invention employs a hybrid analog-digital dual-loop approach, shortening the EDO cancellation time at the input. Furthermore, the analog-to-digital converter in the digital servo circuit has a very low sampling rate, resulting in very low power consumption. This effectively solves the problems of achieving a high EDO suppression range and low input reference noise, as well as the issues of excessively large integrator time constants and long EDO cancellation times in traditional analog DC servo circuits. It is suitable for wearable EEG acquisition systems. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of a method for eliminating DC offset between electrodes in an EEG acquisition device using mixed-signal DSL technology, according to the present invention.

[0035] Figure 2 This is a circuit diagram of a capacitively coupled instrumentation amplifier in the prior art;

[0036] Figure 3A circuit diagram of a capacitively coupled instrumentation amplifier with a chopper added to an existing technology;

[0037] Figure 4 This is a circuit diagram of a capacitively coupled instrumentation amplifier that uses an analog servo circuit in the prior art. Detailed Implementation

[0038] The following detailed description of a typical embodiment of a method for eliminating DC offset between electrodes in an EEG acquisition device using mixed-signal DSL technology according to the present invention provides further specific details of the invention. It is necessary to point out that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made to the present invention by those skilled in the art based on the above description still fall within the scope of protection of the present invention.

[0039] This invention discloses a method for eliminating DC offset between electrodes in EEG acquisition devices using a hybrid analog-digital DSL (Digital-Digital Reference Circuit) technique. This technique overcomes the shortcomings of analog DC servo circuits in the front-end circuit of brain-computer interface (BCI) acquisition chips, which have weak DC offset voltage cancellation capabilities and introduce significant noise. In chopper amplifiers using dry contact electrodes, EDO (Electronic Deflection) as high as ±300mV can occur at the input. Traditional methods employ analog DC servo circuits to avoid chopper amplifier saturation caused by EDO. The principle of the DC servo circuit is that an analog integrator extracts the DC component, including low-frequency bias, from the output signal at the output of the over-the-air (OTA) circuit and feeds it back to the input. This is then subtracted from the input signal and canceled at the OTA input. The first problem with traditional DSL is that the 1 / f noise of the integrator cannot be avoided. VEDO, MAX, and noise are all proportional to the capacitance Chp, making it difficult to achieve a high EDO suppression range and low input reference noise. The second problem is that the integrator time constant is very large, resulting in excessively long feedback times when EDO is high. Compared with traditional analog DC servo circuits, this invention effectively solves the problems of difficulty in achieving high EDO suppression range, low input reference noise, and slow feedback time, and is suitable for wearable EEG acquisition systems.

[0040] like Figure 1 As shown, in the first embodiment of the present invention, a method for eliminating DC offset between electrodes in an EEG acquisition device using mixed-signal DSL technology is provided, comprising the following steps:

[0041] Step S1: The first input signal acquired by the wearable extracranial microelectrode EEG detection device is transmitted to the signal amplification module through the input terminals Vinp and Vinn of the front-end acquisition chip. The signal amplification module amplifies the EEG signal in the first input signal to obtain the initially amplified first amplified EEG signal. The first input signal is also transmitted to the digital DC servo circuit module through the input terminals Vinp and Vinn of the front-end acquisition chip. The digital DC servo circuit processes the EEG signal in the first input signal to obtain the first digital DC component of the EEG signal at the Vinp and Vinn terminals. The first amplified EEG signal is transmitted to the analog DC servo circuit module, which processes the first amplified EEG signal to obtain the corresponding second analog DC component. The first digital DC component and the second analog DC component are converted into alternating current through a capacitor and chopper modulation module and connected to the input terminal of the signal amplification module in opposite directions.

[0042] Step S2: The first amplified EEG signal is transmitted to the programmable gain amplifier module. The programmable gain amplifier module performs secondary amplification on the first amplified EEG signal. The high-pass characteristics provided by the feedback capacitor and feedback resistor are used to filter out the residual DC offset voltage after the mixed-signal DC servo circuit processing, so as to obtain an amplified second amplified EEG signal with consistent DC components.

[0043] Step S3: Input the second EEG signal with the same DC component to the anti-aliasing filter to filter out various harmonic noises, thereby leaving the acquired third EEG signal;

[0044] Step S4: Input the filtered third EEG signal into an analog-to-digital converter to convert the analog signal into a fourth digital EEG signal;

[0045] Step S5: Input the converted fourth EEG digital signal into the digital processing module for processing.

[0046] In this embodiment, the signal amplification module includes a chopper modulation unit, an input capacitor Cin1, a fixed gain amplification unit, and a chopper demodulation unit. Step S1 specifically includes the following sub-steps:

[0047] Step S11: The electrodes worn outside the skull, equipped with an EEG signal acquisition device, pass the acquired input signal through a buffer to ensure that the amplification path is consistent with the non-ideal factors in the digital servo circuit, in order to offset the offset voltage generated by the buffer in the digital DC servo circuit module.

[0048] Step S12: The signal after passing through the buffer is transmitted to the signal amplification module through the input terminal of the signal amplification path. The chopper modulation unit in the signal amplification module performs chopper modulation on the EEG signal in the input signal to avoid the noise in the low frequency part of the amplifier and outputs the chopper-modulated EEG signal.

[0049] Step S13: The chopper-modulated EEG signal is amplified by the input capacitor Cin1 and the fixed gain amplification unit to obtain the initially amplified modulated EEG signal.

[0050] Step S14: The initially amplified modulated EEG signal is transmitted to the chopper demodulation unit for signal demodulation, and the signal is demodulated to the original signal frequency band to obtain the initially amplified first amplified EEG signal.

[0051] In this embodiment, the digital DC servo loop module includes an analog-to-digital converter (ADC), a resistive digital-to-analog converter (R-DAC), a buffer, a chopper modulation unit, and an input capacitor Cin. The first input signal is transmitted to the digital DC servo loop module via the input terminals Vinp and Vinn of the front-end acquisition chip. The ADC in the digital DC servo loop module samples, quantizes, and encodes the EEG signal in the input signal to obtain digital codes for the DC components of the EEG signals at the Vinp and Vinn terminals. The digital codes for the DC components of the EEG signals at the Vinp and Vinn terminals are converted from digital signals to analog signals by the resistive digital-to-analog converter (R-DAC) to obtain the DC level of the original EEG signal. The DC level of the original EEG signal is then boosted by the buffer and output as the first digital DC component.

[0052] It is worth mentioning that the accuracy of the analog-to-digital converter determines whether the digital DSL can work properly, and it needs to be as high as possible.

[0053] In this embodiment, the analog DC servo circuit module includes an integrator unit, a chopper modulation unit, and a capacitor Chp; wherein, the first amplifier EEG signal is transmitted to the analog DC servo circuit module, and the integrator unit in the analog DC servo circuit module filters out the AC component in the first amplifier EEG signal to obtain the DC level of the first amplifier EEG signal, which is the second analog DC component.

[0054] Optionally, the chopping frequency of the chopping modulation unit and the chopping demodulation unit is 6 kHz, ensuring that the gain will not decrease too much due to the modulation and demodulation of the chopping.

[0055] In this embodiment, the fixed-gain amplification unit includes a fixed-gain amplifier, two fixed-feedback capacitors, and two fixed-feedback resistors. The two fixed-gain amplifier terminals are connected to the two fixed-feedback capacitors, and the two fixed-feedback resistors are connected to the outer sides of each of the two fixed-feedback capacitors. The fixed-gain amplifier should be defined as follows:

[0056] Schematic illustration: The fixed-gain amplifier has a gain of 80dB, a bandwidth of 60kHz, an input capacitor Cin1 of 3.6pF, a fixed feedback capacitor of 36fF, and a DC bias consisting of two 100GΩ pseudo-resistors Rfb placed between the amplifier's input and output terminals. i Provided; the gain of the fixed-gain amplifier A1 should be expressed as follows:

[0057] In this embodiment, the programmable gain amplification module includes an input capacitor Cin2 and a variable gain amplification unit. Step S2 specifically includes the following sub-steps: transmitting the first amplified EEG signal to the input capacitor Cin2 and the variable gain amplification unit, and amplifying the signal by adjusting the variable gain to obtain the amplified second amplified EEG signal.

[0058] In this embodiment, the variable gain amplifier unit includes a variable gain amplifier, two variable feedback capacitors for single-pole double-throw switches, and two feedback resistors. The two ends of the variable gain amplifier are connected to the two variable feedback capacitors for the single-pole double-throw switches, and the two feedback resistors are respectively connected to the outside of the two variable feedback capacitors for the single-pole double-throw switches.

[0059] Schematic illustration: the variable gain amplifier has a variable gain of 26dB and 32dB, a bandwidth of 30kHz, and the variable feedback capacitors of the single-pole double-throw switch are 108fF and 54fF, respectively, with a feedback resistor Rfb. i It is 100 G ohms.

[0060] In this embodiment, the anti-aliasing filter removes various harmonic noises, thereby retaining the acquired third EEG signal.

[0061] Optionally, the cutoff frequency for the anti-aliasing filter is set to 220Hz.

[0062] In this embodiment, the analog-to-digital converter inputs the filtered third EEG signal into the analog-to-digital converter module, converting the analog signal with continuous amplitude and time into a discrete digital signal.

[0063] Optionally, the analog-to-digital converter has a precision of 10 bits.

[0064] Meanwhile, a second aspect of this embodiment also provides a system for eliminating DC offset between electrodes in an EEG acquisition device using mixed-signal DSL technology, comprising:

[0065] Signal amplification module: used to amplify the EEG signal in the input signal to obtain an amplified first amplified EEG signal; wherein, the signal amplification module includes a chopper modulation unit, an input capacitor Cin1, a fixed gain amplification unit, and a chopper demodulation unit; the chopper modulation unit is used to chopper modulate the EEG signal to avoid noise in the low-frequency part of the amplifier and output the chopper modulated EEG signal; the input capacitor Cin1 and the fixed gain amplification unit are used to amplify the chopper modulated EEG signal to obtain an initially amplified modulated EEG signal; the chopper demodulation unit is used to demodulate the modulated EEG signal to the original signal frequency band to obtain the first amplified EEG signal;

[0066] A digital DC servo loop module is used to process the EEG signal in the input signal to obtain the first digital DC component of the Vinp and Vinn terminal EEG signals. The digital DC servo loop module includes an analog-to-digital converter (ADC), a resistive digital-to-analog converter (R-DAC), a buffer, a chopper modulation unit, and an input capacitor Cin. The ADC samples, quantizes, and encodes the EEG signal in the input signal to obtain digital codes for the DC components of the Vinp and Vinn terminal EEG signals. The R-DAC converts the digital codes of the Vinp and Vinn terminal EEG signal DC components into analog signals to obtain the DC level of the original EEG signal, which is the first digital DC component. The buffer enhances the driving capability of the DC level of the original EEG signal. The first digital DC component is converted into alternating current by the capacitor and the chopper modulation module and connected to the input terminal of the signal amplification module in opposite directions.

[0067] Analog DC servo circuit module: processes the initially amplified first EEG signal to obtain the corresponding second analog DC component; wherein, the analog DC servo circuit module includes an integrator unit, a chopper modulation unit, and a capacitor Chp; the integrator unit filters out the AC component in the EEG signal, and the DC level of the first amplified EEG signal is the second analog DC component; wherein, the second analog DC component is converted into AC current by the capacitor and the chopper modulation module and connected to the input terminal of the signal amplification module in opposite directions;

[0068] Programmable gain amplifier module: used to perform secondary amplification of the first amplified EEG signal in the input signal to obtain an amplified EEG signal. The high-pass characteristic provided by the feedback capacitor and feedback resistor is used to filter out the residual DC offset voltage after the mixed-signal DC servo circuit processing to obtain an amplified second amplified EEG signal with consistent DC components. The programmable gain amplifier module includes an input capacitor Cin2 and a variable gain amplifier unit. The input capacitor Cin2 and the variable gain amplifier unit are used to adjust the variable gain to amplify the second amplified EEG signal.

[0069] Anti-aliasing filter: filters out various harmonic noises, thus leaving the acquired third EEG signal;

[0070] Analog-to-digital converter: converts analog signals with continuous amplitude and time into discrete fourth EEG digital signals;

[0071] Digital processor: used to process the decoded fourth EEG digital signal to obtain the final EEG signal.

[0072] This invention first transmits the acquired input signal to a signal amplification module via the input terminal of a front-end acquisition chip. The signal amplification module amplifies the EEG signal in the input signal to obtain an initially amplified EEG signal. Then, simultaneously, the acquired input signal is transmitted to a digital DC servo loop module via the input terminal of the front-end acquisition chip. The digital DC servo loop processes the EEG signal in the input signal to obtain the DC component of the input EEG signal. Afterward, the initially amplified EEG signal is transmitted to an analog DC servo loop module, which processes the initially amplified EEG signal to obtain... The DC component is then converted into AC current by a capacitor and a chopper modulation module to cancel the input AC current. The amplified EEG signal is then transmitted to a programmable gain amplifier module, which performs secondary amplification. The amplified EEG signal with the same DC component is then input to an anti-aliasing filter to remove various harmonic noises, leaving the acquired EEG signal. The filtered EEG signal is then input to an analog-to-digital converter (ADC) to convert the analog signal into a digital signal. Finally, the converted digital EEG signal is input to a digital processing module for processing. In chopper amplifiers using dry contact electrodes, EDO (Electronic Direction of Occurrence) can occur at the input of the chopper amplifier up to ±300mV. Traditional methods use analog DC servo loops to avoid chopper amplifier saturation caused by EDO. The principle of the DC servo loop is that the analog integrator samples the DC component at the output of the OTA (Over-The-Air) and cancels it at the input of the OTA. The problem with traditional DSLs is that the 1 / f noise of the integrator cannot be avoided. EDO，MAXBoth noise and capacitance (Chp) are proportional, making it difficult to achieve a high EDO suppression range and low input reference noise. Compared to traditional analog DC servo circuits, this invention employs a hybrid analog-digital dual-loop approach, shortening the EDO cancellation time at the input. Furthermore, the analog-to-digital converter in the digital servo circuit has a very low sampling rate, resulting in very low power consumption. This effectively solves the problems of achieving a high EDO suppression range and low input reference noise, as well as the issues of excessively large integrator time constants and long EDO cancellation times in traditional analog DC servo circuits. It is suitable for wearable EEG acquisition systems.

[0073] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A method for eliminating DC offset between electrodes in an EEG acquisition device using mixed-signal DSL technology, characterized in that, Includes the following steps: Step S1: The first input signal acquired by the wearable extracranial microelectrode EEG detection device is transmitted to the signal amplification module through the input terminals Vinp and Vinn of the front-end acquisition chip. The signal amplification module amplifies the EEG signal in the first input signal to obtain the initially amplified first amplified EEG signal. The first input signal is also transmitted to the digital DC servo circuit module through the input terminals Vinp and Vinn of the front-end acquisition chip. The digital DC servo circuit processes the EEG signal in the first input signal to obtain the first digital DC component of the EEG signal at the Vinp and Vinn terminals. The first amplified EEG signal is transmitted to the analog DC servo circuit module, which processes the first amplified EEG signal to obtain the corresponding second analog DC component. The first digital DC component and the second analog DC component are converted into alternating current through a capacitor and chopper modulation module and connected to the input terminal of the signal amplification module in opposite directions. Step S2: The first amplified EEG signal is transmitted to the programmable gain amplifier module. The programmable gain amplifier module performs secondary amplification on the first amplified EEG signal. The high-pass characteristics provided by the feedback capacitor and feedback resistor are used to filter out the residual DC offset voltage after the mixed-signal DC servo circuit processing, so as to obtain an amplified second amplified EEG signal with consistent DC components. Step S3: Input the second EEG signal with the same DC component to the anti-aliasing filter to filter out various harmonic noises, thereby leaving the acquired third EEG signal; Step S4: Input the filtered third EEG signal into an analog-to-digital converter to convert the analog signal into a fourth digital EEG signal; Step S5: Input the converted fourth EEG digital signal into the digital processing module for processing.

2. The method for eliminating DC offset between electrodes in an EEG acquisition device using mixed-signal DSL technology as described in claim 1, characterized in that, The signal amplification module includes a chopper modulation unit, an input capacitor Cin1, a fixed gain amplification unit, and a chopper demodulation unit. Step S1 specifically includes the following sub-steps: Step S11: The electrodes worn outside the skull, equipped with an EEG signal acquisition device, pass the acquired input signal through a buffer to ensure that the amplification path is consistent with the non-ideal factors in the digital servo circuit, in order to offset the offset voltage generated by the buffer in the digital DC servo circuit module. Step S12: The signal after passing through the buffer is transmitted to the signal amplification module through the input terminal of the signal amplification path. The chopper modulation unit in the signal amplification module performs chopper modulation on the EEG signal in the input signal to avoid the noise in the low frequency part of the amplifier and outputs the chopper-modulated EEG signal. Step S13: The chopper-modulated EEG signal is amplified by the input capacitor Cin1 and the fixed gain amplification unit to obtain the initially amplified modulated EEG signal. Step S14: The initially amplified modulated EEG signal is transmitted to the chopper demodulation unit for signal demodulation, and the signal is demodulated to the original signal frequency band to obtain the initially amplified first amplified EEG signal.

3. The method for eliminating DC offset between electrodes in an EEG acquisition device using mixed-signal DSL technology as described in claim 1, characterized in that, The digital DC servo loop module includes an analog-to-digital converter (ADC), a resistive digital-to-analog converter (R-DAC), a buffer, a chopper modulation unit, and an input capacitor Cin. The first input signal is transmitted to the digital DC servo loop module via the input terminals Vinp and Vinn of the front-end acquisition chip. The ADC in the digital DC servo loop module samples, quantizes, and encodes the EEG signal in the input signal to obtain digital codes for the DC components of the EEG signals at the Vinp and Vinn terminals. The digital codes for the DC components of the EEG signals at the Vinp and Vinn terminals are converted from digital signals to analog signals by the resistive digital-to-analog converter (R-DAC) to obtain the DC level of the original EEG signal. The DC level of the original EEG signal is then boosted by the buffer and output as the first digital DC component.

4. The method for eliminating DC offset between electrodes in an EEG acquisition device using mixed-signal DSL technology as described in claim 1, characterized in that, The analog DC servo circuit module includes an integrator unit, a chopper modulation unit, and a capacitor Chp; wherein, the first amplifier electroencephalogram (EEG) signal is transmitted to the analog DC servo circuit module, and the integrator unit in the analog DC servo circuit module filters out the AC component in the first amplifier EEG signal to obtain the DC level of the first amplifier EEG signal, which is the second analog DC component.

5. The method for eliminating DC offset between electrodes in an EEG acquisition device using mixed-signal DSL technology as described in claim 2, characterized in that, The fixed-gain amplification unit includes a fixed-gain amplifier, two fixed-feedback capacitors, and two fixed-feedback resistors. The two fixed-feedback capacitors are connected to the two ends of the fixed-gain amplifier, and the two fixed-feedback resistors are connected to the outer sides of each of the two fixed-feedback capacitors. The fixed-gain amplifier should be expressed as follows:

6. The method for eliminating DC offset between electrodes in an EEG acquisition device using mixed-signal DSL technology as described in claim 1, characterized in that, The programmable gain amplification module includes an input capacitor Cin2 and a variable gain amplification unit. Step S2 specifically includes the following sub-steps: transmitting the first amplified EEG signal to the input capacitor Cin2 and the variable gain amplification unit, and amplifying the signal by adjusting the variable gain to obtain the amplified second amplified EEG signal.

7. The method for eliminating DC offset between electrodes in an EEG acquisition device using mixed-signal DSL technology as described in claim 6, characterized in that, The variable gain amplifier unit includes a variable gain amplifier, two variable feedback capacitors for single-pole double-throw switches, and two feedback resistors. The two ends of the variable gain amplifier are connected to the two variable feedback capacitors for the single-pole double-throw switches, and the two feedback resistors are respectively connected to the outside of the two variable feedback capacitors for the single-pole double-throw switches.

8. The method for eliminating DC offset between electrodes in an EEG acquisition device using mixed-signal DSL technology as described in claim 1, characterized in that, The anti-aliasing filter removes various harmonic noises, thus leaving the acquired third EEG signal.

9. A method for eliminating DC offset between electrodes in an EEG acquisition device using mixed-signal DSL technology as described in claim 1, characterized in that, The analog-to-digital converter inputs the filtered third EEG signal into the analog-to-digital converter module, converting the analog signal with continuous amplitude and time into a discrete digital signal.

10. A system for eliminating DC offset between electrodes in an EEG acquisition device using mixed-signal DSL technology, characterized in that, include: Signal amplification module: used to amplify the EEG signal in the input signal to obtain an amplified first amplified EEG signal; wherein, the signal amplification module includes a chopper modulation unit, an input capacitor Cin1, a fixed gain amplification unit, and a chopper demodulation unit; the chopper modulation unit is used to chopper modulate the EEG signal to avoid noise in the low-frequency part of the amplifier and output the chopper modulated EEG signal; the input capacitor Cin1 and the fixed gain amplification unit are used to amplify the chopper modulated EEG signal to obtain an initially amplified modulated EEG signal; the chopper demodulation unit is used to demodulate the modulated EEG signal to the original signal frequency band to obtain the first amplified EEG signal; A digital DC servo loop module is used to process the EEG signal in the input signal to obtain the first digital DC component of the Vinp and Vinn terminal EEG signals. The digital DC servo loop module includes an analog-to-digital converter (ADC), a resistive digital-to-analog converter (R-DAC), a buffer, a chopper modulation unit, and an input capacitor Cin. The ADC samples, quantizes, and encodes the EEG signal in the input signal to obtain digital codes for the DC components of the Vinp and Vinn terminal EEG signals. The R-DAC converts the digital codes of the Vinp and Vinn terminal EEG signal DC components into analog signals to obtain the DC level of the original EEG signal, which is the first digital DC component. The buffer enhances the driving capability of the DC level of the original EEG signal. The first digital DC component is converted into alternating current by the capacitor and the chopper modulation module and connected to the input terminal of the signal amplification module in opposite directions. Analog DC servo circuit module: processes the initially amplified first EEG signal to obtain the corresponding second analog DC component; wherein, the analog DC servo circuit module includes an integrator unit, a chopper modulation unit, and a capacitor Chp; the integrator unit filters out the AC component in the EEG signal, and the DC level of the first amplified EEG signal is the second analog DC component; wherein, the second analog DC component is converted into AC current by the capacitor and the chopper modulation module and connected to the input terminal of the signal amplification module in opposite directions; Programmable gain amplifier module: used to perform secondary amplification of the first amplified EEG signal in the input signal to obtain an amplified EEG signal. The high-pass characteristic provided by the feedback capacitor and feedback resistor is used to filter out the residual DC offset voltage after the mixed-signal DC servo circuit processing to obtain an amplified second amplified EEG signal with consistent DC components. The programmable gain amplifier module includes an input capacitor Cin2 and a variable gain amplifier unit. The input capacitor Cin2 and the variable gain amplifier unit are used to adjust the variable gain to amplify the second amplified EEG signal. Anti-aliasing filter: filters out various harmonic noises, thus leaving the acquired third EEG signal; Analog-to-digital converter: converts analog signals with continuous amplitude and time into discrete fourth EEG digital signals; Digital processor: used to process the decoded fourth EEG digital signal to obtain the final EEG signal.

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