RU225363U1 - Active RC second-order notch filter with independent adjustment of three parameters for electrophysiological signals (EPS) - Google Patents

Abstract

The utility model relates to instrument making and can be used in components of radio-electronic electrophysiological devices. The technical result of the utility model is to ensure stability of the value of the quality factor of the pole of an active RC notch filter of the second order with independent adjustment of three parameters for processing electrophysiological signals when adjusting the transmission coefficient and expanding the dynamic range of changes in the amplitude of the input voltage at the extreme positions of the potentiometer slide. An active RC notch filter of the second order with independent tuning of three parameters for processing electrophysiological signals is made on four differential operational amplifiers (DOA) with a frequency-selective circuit based on a parallel connected integrator and differentiator and two DOAs with independent adjustment of the notch frequency, transmission coefficient and pole quality factor using one potentiometer and two variable resistors. Independence of parameter adjustment is ensured by switching the DOU to inverting mode and introducing two additional resistors. The quality factor is adjusted by changing the resistance of the variable resistor of the output resistive divider in the negative feedback channel, which is not connected to the direct input voltage transmission channel. Expansion of the dynamic range of the input voltage at the extreme positions of the potentiometer slide for setting the notch frequency is ensured by reducing the amplitude of the voltage supplied to the inputs of the integrator and differentiator by 3 times. 1 table, 5 ill.

Description

The utility model relates to instrument making and can be used in components of radio-electronic electrophysiological devices. When transmitting electrophysiological signals, before their analog-to-digital conversion, pre-processing is required, which includes, as a mandatory element, filtering of unwanted frequencies in the spectrum of the input signal. At the same time, the independence of the values of the transmission coefficient, pole quality factor and rejection frequency from each other ensures the convenience of specifying three filter parameters without iterative procedures.

Tunable notch filters are known that provide suppression of a given frequency. Tunable notch filter [Kaduk B.G., Rovensky A.Ya., Fidman B.G. A.s. SU 327571 dated January 26, 1972], containing an inverting integrator and differentiator, which, using two output potentiometers, allows you to change the voltage transfer coefficient, while two input potentiometers regulate the level of the signal supplied to the inputs of the integrator and differentiator. The output voltage is summed across the inverting operational amplifier.

The disadvantage of the filter is the possibility of the integrator going into a saturation state, as a result of which the circuit cannot function normally as a notch filter due to the lack of general negative feedback (NFE) covering the filter integrator.

A tunable inverting notch filter is known [Ostapenko A.G. A.s. SU 849450 dated July 23, 1981], which provides tuning of the notch frequency over a wide range using a dual potentiometer.

The circuit contains 6 amplifiers. The filter includes an inverting integrator and differentiator, as well as an output inverting current combiner on the operational amplifier. The input voltage from input to output undergoes inversion by a differential adder on inverters, current-to-voltage converters, then an inverting integrator and differentiator, as well as an inverting adder.

The disadvantage of the filter is the lack of quality control and the use of a dual potentiometer to adjust the frequency.

As a prototype for the proposed tunable active RC notch filter for electrophysiological signals, the “Tunable active RC notch filter for electrophysiological signals” was selected [Belov A.V. and others. Patent for PM RU 207908 U1 dated November 23, 2021].

The prototype filter contains an inverting integrator (1) and a differentiator (2), a potentiometer (3), a resistive voltage divider (4) containing resistors (13, 14), a differential operational amplifier (DOA) (5), switched on in voltage follower mode , output DOU (6), compensation resistor (7), limiting resistors (8, 9), output resistive divider (10) containing resistors (11, 12) and the non-inverting input of the output DOU (6) is connected to the potentiometer slider (3) , and its output is the filter output, the output of the voltage divider (4) is connected to the input of the DOU (5), while the output of the resistor (13) is connected to the filter input, and the output of the resistor (14) is connected to the filter output, the output of the DOU (5) is connected the first output of the compensation resistor (7) is connected to the common input of the inverting integrator (1) and differentiator (2), the first output of the compensation resistor (7) is connected to the output of the potentiometer engine (3), the second output is connected to the common wire, limiting resistors (8, 9) are connected to the outputs of the inverting integrator ( 1) and differentiator (2) and to the potentiometer terminals (3), the output of the resistive divider (10) is connected to the inverting input of the DOU (6), the resistor terminal (11) is connected to the common wire.

The disadvantages of the prototype filter are:

dependence of the transmission coefficient Ko on the quality factor of the pole Q;

limitation of the dynamic range of the input voltage amplitude at the extreme positions of the potentiometer slide.

The objective of the proposed invention is to eliminate the listed disadvantages of the prototype.

The solution to the problem of ensuring the stability of the value of the quality factor of the pole of an active RC notch filter of the second order with independent adjustment of three parameters for processing electrophysiological signals when adjusting the transmission coefficient is achieved by transferring the DOE (5, 6) of the prototype filter to the inverting operating mode and introducing two additional resistors (15 , 16).

Expansion of the dynamic range of changes in the amplitude of the input voltage at the extreme positions of the potentiometer slide is ensured by reducing the transmission coefficient in the negative feedback loop (NFL) for setting the quality factor of the Q pole by three times.

The utility model is illustrated by drawings, where

in fig. Figure 1 shows a schematic diagram of the prototype “Tunable active RC notch filter for electrophysiological signals”;

in fig. Figure 2 shows a schematic diagram of the proposed second-order active RC notch filter with independent adjustment of three parameters for processing electrophysiological signals;

in fig. 3 - frequency response graphs of the proposed notch filter for various values of the pole quality factor Q and transmission coefficient Ko at a constant notch frequency;

in fig. 4 - graphs of the dependence of the values of the quality factor of the pole quality factor Q on the transmission coefficient K of the prototype circuits and the claimed device;

in fig. Figure 5 shows a time graph of the amplitudes of the input and output voltages of the proposed notch filter at a maximum deviation from the central notch frequency and an input voltage amplitude of 11 V.

The proposed device works as follows.

The device is an inverting input voltage, since all four DOUs (1,2,5,6) operate in inverting mode. The inputs of the inverting integrator (1) and differentiator (2) are connected to the output of the first DOU (5) and are covered by the OOS circuit through a potentiometer (3), the second DOU (6) with an output resistive voltage divider (10) and an input resistive voltage divider (4) , the output of which is connected to the inverting input of the DOU (5). On direct current, i.e. at a frequency equal to zero, the transmission coefficient of the inverting differentiator (2) is close to zero, and the transmission coefficient of the inverting integrator (1) is maximum.

Transfer coefficient Ko at frequencies sufficiently distant from the notch frequency Freg. towards both lower and higher frequencies is constant, due to the action of the feedback loop, covering the inverting integrator (1) and differentiator (2), potentiometer (3) and output DOU (6) with an output resistive voltage divider (10 setting the gain of the DOU (6). When the potentiometer slider (3) is in the middle position at the central notch frequency, the modules of the integrator (1) and differentiator (2) transmission coefficients are equal, and the output voltages are antiphase, since at any operating frequency the phase shift between them is constant and amounts to 180°. As a result, the total voltage from the inverting integrator and differentiator (1, 2) at the output of the potentiometer (3) will also be close to zero. The voltage at the notch frequency at the output of the DOE (6), and, consequently, at the filter output ( 18), will also be close to zero. The notch frequency at the middle position of the potentiometer slider (3) is determined by the values of the inverting integrator (1) Tint and differentiator (2) Tdiff. time constants, which are usually chosen equal.

Maintaining the voltage close to zero at the output of the potentiometer (3) at different output voltages inverting the integrator (1) and differentiator (2), when the frequency changes, is ensured by different positions of the potentiometer (3), i.e. transmission coefficient. At a fixed input voltage of the inverting integrator (1), its output voltage increases as the frequency decreases, and the output voltage of the inverting differentiator (2) decreases, i.e. When the potentiometer slider (3) moves towards the output, the output voltage of the inverting integrator (1) decreases, and the output voltage of the inverting differentiator (2) increases. In this case, the zero voltage at the output of the potentiometer (3) will be at a frequency higher than the notch frequency Freg corresponding to the middle position of the potentiometer slider (3).

When the potentiometer slider (3) moves towards the output of the inverting differentiator (2), its output voltage decreases, and the output voltage of the inverting integrator (1) increases. The zero voltage at the output of the potentiometer (3) will be at a frequency below the notch frequency corresponding to the middle position of the potentiometer slider (3).

Thus, when changing the position of the potentiometer slider, the notch frequency Freg is adjusted. The correction resistor (7) between the potentiometer slider (3) and the inverting input of the DOE (6) reduces the depth of the overall OOS of the filter and reduces the maximum achieved quality factor of the Q pole, while maintaining a constant value of the quality factor when adjusting the notch frequency, i.e. when moving the potentiometer slider (3).

The values of the quality factor of the poles of the prototype Qpp and the proposed filter Q3, obtained as a result of modeling in the Microcap 12 program, with a change in the transmission coefficient Ko are shown in the table.

From the results obtained, it follows that connecting a compensation resistor (7) between the potentiometer slider (3) and the inverting input of the DOE (6) ensures stability of the quality factor of the filter pole when adjusting the notch frequency by reducing it by 2.5 times from the maximum achieved value. Limiting resistors (8, 9) between the outputs of the inverting integrator (1) and differentiator (2) allow you to move the potentiometer slider (3) from one output to the other, i.e. use the entire range of movement of the engine, while ensuring adjustment of the notch frequency.

The proposed scheme of an active RC notch filter of the second order with independent tuning of three parameters for processing electrophysiological signals makes it possible to independently adjust three parameters: filter notch frequency Freg., without changing the quality factor of the pole Q, transmission coefficient Ko, and also increase the dynamic range of the input voltage amplitude at extreme positions of the potentiometer slide to a voltage close to the supply voltage of the DOU, which increases manufacturability, ease of setup and adjustment of the parameters of an active RC notch filter of the second order with independent adjustment of three parameters for processing electrophysiological signals, both during production and during operation.

BIBLIOGRAPHICAL LIST

1. Patent SU 430484 A1, 1974

2. Patent SU 510776 A1, 1974

3 Patent SU 1146797 Al, 1985

4. Patent SU 849450 A1, 1981

5. Patent SU 1788570 A1, 1993

6. Patent RU 199745 U1, 2020

7. Patent RU 207908 U1, 2021

8. Patent RU 149838 U1, 2019

9. Patent RU 170069 U1, 2017

10. Patent RU 2701038 C1, 2019

11. Patent RU 2110140 C1, 1998

12. Patent RU 2169430 C1, 2001

13. Patent RU 2019024 C1, 1994

14. Patent RU 2019025 C1, 1994

Claims (1)

Active RC notch filter of the second order with independent adjustment of three parameters for processing electrophysiological signals, containing: an inverting integrator (1) and a differentiator (2) with a common input; input resistive voltage divider (4), consisting of a variable resistor (13) and a constant resistor (14); first and second differential operational amplifiers (DOA) (5, 6); output resistive voltage divider (10), consisting of a variable resistor (11) and a constant resistor (12); resistive voltage divider for tuning the notch frequency with a potentiometer (3) and two limiting resistors (8, 9); compensation resistor (7), and the first output of the compensation resistor (7) is connected to the potentiometer motor (3), the output of the first DOU (5) is connected to the common input of the inverting differentiator (1) and integrator (2), limiting resistors (8, 9) connected to the outputs of the inverting integrator (1) and differentiator (2) and to the terminals of the potentiometer (3); the output of the second DOU (6) is the output of the filter (18), the output of the variable resistor (13) of the voltage divider (4) is the input of the filter (17), the resistors (12, 14) of the resistive dividers (4, 10) are interconnected and connected to filter output (18), a variable resistor (11) of the output resistive voltage divider (10) is connected to a common wire (19), characterized in that two resistors (15, 16) are inserted, and the resistor (15) is connected between the inverting input and output DOU (5), resistor (16) is connected to the inverting input of the DOU (6) and to the output of the output resistive divider (10), the second output of the compensation resistor (7) is connected to the inverting input of the DOU (6), non-inverting inputs of the first and second DOU ( 5, 6) are connected to a common wire (19), the output of the input resistive voltage divider (4) is connected to the inverting input of the DOU (5).

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