CZ2010509A3 - System for measuring biological signals with suppression of interference - Google Patents

Abstract

The system for measuring bioelectric signals with effective common mode interference suppression includes three electrodes (e.sub.1, e.sub.2, e.sub.3) and two non-differential amplifiers (ZS6, ZS7). The patient from whose body biopotentials are sensed is connected to the inverting amplifier ZS7. The interference suppression system is based on measuring the voltage between two electrodes (e.sub.1) and (e.sub.2) located on the human body. The sensed voltage is amplified by an amplifier (ZS6), whereby a third electrode (e.sub.3) excited by an inverting amplifier (ZS7) is used to minimize the effect of interference on the measured signal. The electrode (e.sub.2) is connected to the inverting amplifier input (ZS7) and the inverting amplifier output (ZS7) is connected to the electrode (e.sub.3). The electrode (e.sub.1) is connected to the input of the amplifier (ZS6), from which the measured voltage can be extracted (V.sub.O.n.). This achieves effective suppression of external interference by using two metering amplifiers.

Description

System for measuring biological signals with interference suppression

Field of technology

The present invention relates to biological signal measurement systems, such as an EEG electroencephalograph, an ECG electrocardiograph, and the like. Specifically, it is a task to measure from the surface or inside a living organism, especially the human body, the potential difference, which corresponds to the activity of living tissues.

State of the art

The situation common in measuring biological signals is shown in FIG. _la . The electrodes e, a _& are connected to the human body and their signal is measured by a differential amplifier ZS1, which amplifies the potential difference of the electrodes and converts it to the output voltage, V _a . At the same time, however, there is also a source of interference, which most often corresponds to the electricity distribution network. The interference penetrates into the measured person through the impedances _Ž1 and _δ . which are typically formed by the parasitic capacitances of the boundary, human, and interfering source. The interfering source and the measuring amplifier usually have their zero potentials GND1 and GND2 separately. whose interconnection can be illustrated by impedance In the galvanic separation of both potentials, this impedance represents Z _and the parasitic capacitance between the zero potentials GND1 and GND2. These changes can then be transmitted to the output of the differential amplifier ZS1 as an interfering voltage.

To describe the way in which the interference reaches the output of the real measuring differential inverter ZSt and the associated techniques which try to suppress this interference, the situation in FIG. The source of interference and impedance Z ,, Zz, _& are represented here by the replacement ^Theven , the new circuit V ₅ and _& . ^and & represent the impedance of the electrodes and, respectively, their imperfect contact and the impedance of the surface tissue.

ZZ; ~ ^{JS Ζ06 represents the} amplifier _Z1 input impedances and Zys. In addition, a galvanic path to zero potential must be implemented in these input impedances Z and _Z to make the input circuits of the differential network. The ideal conditions _for the impedances are identical _and the input impedances are identical. In this case, both inputs are ideal for Z? - ^β8 ° ^ν30 θ ~ ^{naPě 3} ^ ' ^{UPni napě, i is} u ^ regardless of I, ost rusweho voltage Vs. Under real conditions, however, the impedances ZE1 and ZE2 Z are ^{vTZT , and} a different voltage amplifier DZ1 then appears at both inputs of the ideal differential amplifier DZ1, and the voltage Vc thus begins to fan the voltage V _and

Several methods have been proposed to suppress this phenomenon. Various connections of measuring amplifiers have been proposed which 7 ^ 7 ·.

impedance Z _and 7 provided large values of input pedances and _& cm is suppressed! the effect of the difference in impedance Z1 and _{E2 as} reported in A. Miller. Coupling circuit with driven guard, ufepatent 4 191 1 _{95 1978} or in NV Thakor and JG Webster Ground electrodes ifff _Tra , Ground-free ecg recording with two

980 T f 7 θ ' ^{1 BiOmedCa} ' ^ -27 (12) ^ 04. This reset usually does not allow the mentioned galvanic connection of the inputs of the measuring "with zero potential" and moreover this approach is often insufficient.

From t _a ' ^{ΡΠ8, υΡυ} ' θ ^{to Ρ} ° ^ϋΖί “ ^{e, ek, r} ° ^dy ' ^Μ θ ^ΓΖ “ «for example ad ΓΖ' ^T ° ^{this is} stated, for example, by B. Winter and JG Webster. Reduction of interference due to common mode voltage in biopotentia! amplifiers. IEEE Transactions on BioZca Engineering, _BM E-30 (1) _{: 58} ^, i ₉₈₃ . _{The specific situation is to} replace the circuit shown in Fig. 2b. The third electrode is denoted here as e ₃ and its mpedance is denoted as fe. The function of this circuit is similar to that of circuit z

Fig. 1b, with the difference that if the impedance Z _H of the third electrode e ₃ is sufficiently small, it causes a reduction of the disturbing nan V and thus - * “ ^{3 f} . *. ^{This reduces} the overall effect of interference _{on the} output, voltage V _and . The input _impedances Z * and in this case represent the input impedance of the amplifier used. In the case of MOSFET implementation, it is only the internal capacity or the residual current of the gate. There are. _{however, the} vastly small values of the impedance Z _and the third electrode e ₃ can be reached even in the case. It is used so-called dry electrodes which X "application, but _{a considerable transition} ^to ° ^br · ^3a ' ^To ' ° _zapo ' ^ani * ~ ^euman . Biopotential amplifiers. In JG Webster editor at the station, John Wiley _& Sons. 1 ^, _{or v} q _{Prutchi and M} “° ^f Γ“ '* Sons. 2005 or Article B, Winter and JG _Webster . Driven-right-leg circuit design IEEE Transactions on Biomedical Engineering. BME-30 (1) 62¾ Ι9 _β3 This ““ θ - - Driven _Ri ght ”Cir ^ í ~ as a circuit is not the tension of the right foot. The right foot is stated because in practice the output of this circuit is often connected to this place. This circuit is arranged by “signa! from the first electrode e, and from the second electrode e, the processing of the amplifiers 7 ^ 2 => ^J is processed by means of two ^{252 and} the voltage ^of these amplifiers ZS2 and ^ZS3 is summed by the electrodes ⁶ ~ ^{Se Back and} converting The output of the amplifiers ZS2 and ^ZS3 is assisted by the differential amplifier ZS5. Amplifiers ZS2 and ZS3 and zaoo ^ H Ί ^2eS11 ° ^VaC ^ - ^{in Fig. 3a} j ^are real amplifiers. The principle of operation of this circuit _{can be used to replace it}

S3 are modeled here as a combination of ideal amplifiers _ZZ2 and 5a P decent input Impedance & a _& a real Invert! the amplifier creates ^{a Xo} _VertUjiC . ^{It is obvious that} the circuit ^ is a negative feedback loop which is h / ^nø _Qn ^ x. -.

772 o '.j ί - ^{Y <KThera} is made by ideal amplifiers 77?

ZZ3 and the ideal inverting amplifier 774 τ ♦ - --- ' _n ^{J z} «inverter ZZ4. This loop minimizes the sum voltage of the output amplifiers ZZ2 and _ZZ3 . that it acts against ruěiZnX pnpade. from the amplification of the ideal inverting amplifier ZZ4 grows above all

e. must sum voltage! outputs of the amplifiers ZZ2 and ZZ3 are connected to nu.e

In the case of unbalanced signal paths, COZ is only achieved by this. that the converting amplifier ZZ4 resets the voltage V _{s with} its output and thus removes the effect.

ideal interference

This involvement has proven to be a highly effective way of suppressing network interference by sensing biological signals. However, its disadvantage is the more complex circuit resent, which requires the use of four amplifiers, one of which is differential

The essence of the invention

The proposed system for measuring biological signals with interference suppression consists in the use of the principles of 100% negative feedback with the help of three electrodes and only amplifiers with a common zero potential. The essence of the new solution is that the first electrode is connected to the input of the amplifier, the output of which is the output of the system. The second electrode is connected to the input of the inverting amplifier, to the output of which the third electrode is connected. The amplifier and inverting amplifier have a common zero potential. ^J

In a particular embodiment, the inverting amplifier can be implemented, for example, by a non-feedback operational amplifier, whose inverting input is connected to the second electrode, its non-inverting input is connected to zero potential and its output is connected to the third electrode.

The advantage of the proposed solution is a simpler circuit solution, which requires the use of only two amplifiers, none of which may be differential.

, 'Description of the figures in the drawings

Figures 1a to 3b show the prior art. The attached Fig. 1a shows a system for measuring biological signals in a two-point measurement of biological signals, and Fig. Tb shows a simplified spare circuit of the situation of Figs. the. Giant. 2a shows the situation in a three-point measurement of biological signals and its pneeling, FIG. 2b shows a simplified spare circuit of the situation of FIG. 2a. Giant. 3a shows the situation in a three-point measurement of biological signals using the Driven Right Leg Circuit, the simplified replacement circuit of which is shown in

An example of a system for measuring biological signals with suppression of drying according to the present invention is then shown in Fig. 4a. Fig. 4b shows a simplified replacement circuit of the circuit of Fig. 4a.

Embodiment / embodiment of the invention

An example of an embodiment of the proposed arrangement of a system for measuring biological signals is shown in Fig. 4a. The amplifier ZS6 is connected to the first electrode e by its input, and an amplified output signal is taken at its output. The inverting amplifier ZS7 is connected to the second electrode by its input and its output is connected to the third electrode &. The gain of the amplifier ZS6 is given by the requirement to amplify the differential voltage, limit, the first electrode e, and the second electrode _fc . The gain of the ZS7 inverting amplifier is negative and as large as possible in absolute value, ideally infinite. To achieve this goal, it is advantageously possible, for example, to use an operational amplifier without feedback. The non-inverting amplifier and the inverting amplifier have a common zero potential.

To explain the function of this arrangement, Fig. 4b shows a simplified replacement circuit, the impedance of the first electrode e ,. the second electrodes e, and the third electrodes _& are represented here by the spare impedances, namely at the spare impedance the second spare impedance Z _E2 and the third spare impedance

The real amplifier ZS6 is represented here by the ideal amplifier ZZ6 and the first input impedance Z »and the real inverting amplifier ZSZ is represented by the ideal converting amplifier _{ZZ7 and} the second input impedance Z„ All sources of interfering voltages are represented by a signal source V 1 is also included, which represents the tension generated by the biological tissues in the subject being measured. It is obvious that the negative feedback loop consists of an ideal inverting amplifier ZZ7, a second surrogate impedance, a third surrogate impedance Z _EJ and a second input impedance Z _v7 . The presence of this loop causes that at its input will be zero Due to the zero input current of the ideal inverting amplifier ZZ7, then, the voltage Ve will be zero. This eliminates the presence of interference in node C. The output voltage Yp is then given only by the signal source by the impedance divider formed by the first spare impedance _& and the first input impedance Z1 and the gain of the ideal amplifier ZZ6. The interference source Vs does not affect the output voltage V _Q.

Like the Driven Right Leg Circuit, the circuit in Figure 4a is able to eliminate interference, but it is implemented with a much simpler circuit, where only two non-differential amplifiers are used instead of four amplifiers, one of which must be differential.

For completeness, a description of the function of the system with real components according to r.4a is given. The ZS6 amplifier amplifies the voltage of the first electrode against a common zero potential. The inverting amplifier ZS7 amplifies the voltage of the second electrode _& again against the common zero potential and its output voltage is fed back to the subject via the third electrode _& inverting amplifier ZS7 thus creates a 100% negative feedback loop which closes through the measured subject and causes. that the potential at the application point of the second electrode & will be almost identical to the zero potential of the amplifier ZS6 and the inverting amplifier ZS7 The output voltage of the amplifier ZS6 then corresponds to the differential voltage between the electrode e affected by other sources of interference while requiring the use of only two ordinary non-differential amplifiers.

Industrial applicability

The invention can be used to measure biological signals, such as electroencephalogram, electrocardiogram. and the like, while being resistant to electromagnetic interference. Its advantage is a simple circuit solution

Claims (2)

PATENT CLAIMS A system for measuring biopotentials consisting of three electrodes for connection to a living organism and two amplifiers, characterized in that the first electrode (e,) is connected to the input of an amplifier (ZS6). whose output is the output of the system, the second electrode (¾) is connected to the input of the inverting amplifier (ZS7), to the output of which the third electrode (e ₃ ) is connected, the amplifier (ZS6) and the inverting amplifier (ZS7) having a common zero potential. Biopotential measurement system according to claim 1, characterized in that the converting amplifier (ZS7) is formed by a non-feedback operational amplifier, the inverting input of which is connected to the second electrode (e ₂ ), its non-inverting input is connected to zero potential and its the output is connected to the third electrode (e ₃ ).