RU218616U1 - Adjustable mains frequency notch filter for physiological signal processing - Google Patents

Abstract

The utility model relates to notch filter circuits with controlled quality and is intended for use in electrophysiological equipment for filtering signals from interference at a mains frequency of 50 or 60 Hz. The technical result of the utility model is to ensure the operation of an adjustable notch filter of the mains frequency for processing physiological signals at the maximum amplitude of the input voltage at the notch frequency and the maximum specified quality factor. In the adjustable network frequency notch filter for processing physiological signals, a limiting resistor (6) is connected between the second output of the potentiometer (2) and the output of the original non-inverting notch filter (3). A resistive voltage divider (5) is connected between the input of the adjustable network frequency notch filter for processing physiological signals and the common wire of the power source (4), the output of which is connected to the non-inverting input of the differential operational amplifier (1). An amplifier (7) is connected to the output of the original non-inverting notch filter (3), the output of which is the output of an adjustable mains frequency notch filter for processing physiological signals. 7 ill.

Description

The utility model adjustable mains frequency notch filter for physiological signal processing refers to notch filter circuits with controlled quality factor and is intended for use in electrophysiological equipment devices for filtering signals from interference at a mains frequency of 50 or 60 Hz.

Notch filters are widely used in life science systems, communication systems, audio systems and various measuring instruments. These filters provide attenuation of the input signal to -30 to -60 dB at the notch frequency. This is especially true when suppressing mains frequency interference 50/60 Hz.

Typically, notch filters require the passband gain of the filter to be unity. It is also required to provide the possibility of adjusting the value of the quality factor of the filter Q in a wide range while maintaining the constancy of the value of the transmission coefficient in the passband.

Notch filters are among the fairly common analog devices that determine the quality indicators of many radio engineering systems, including those for digital signal processing [1–27]. In this class of devices, a special place is occupied by notch filters with independent Q-switching [28–31].

The closest analogue in terms of essential features to the proposed network frequency notch filter for processing physiological signals is an adjustable active notch filter according to utility model patent No. RU 59911 U1. (Belov A.V. et al., class H03N 7/12, issued 12/27/2006). This filter is chosen as a prototype.

In FIG. 1 shows a diagram of an adjustable active notch filter - a prototype. The adjustable active notch filter contains: a differential operational amplifier (1), a potentiometer (2), the slider of which is connected to the inverting input of the differential amplifier 1; the first output of the potentiometer 2 is connected to the connection point of the output of the differential operational amplifier 1 and the input of the original non-inverting notch filter, the second output of the potentiometer 2 is connected to the output of the active notch filter; the original non-inverting notch filter (3), the original non-inverting notch filter (3) has a common ground connection. The output of the adjustable active notch filter is the output of the original non-inverting notch filter. The input of the adjustable active notch filter is the non-inverting input of the differential operational amplifier 1.

The advantage of the prototype circuit is the ability to adjust the quality factor of the filter using a potentiometer using only negative feedback.

The disadvantage of the prototype is the limitation of the maximum allowable input voltage at the notch frequency when setting the maximum quality factor of the filter.

The objective of the proposed utility model is to exclude a decrease in the amplitude of the input voltage of the adjustable notch filter at the notch frequency when the value of the quality factor of the adjustable notch filter is increased.

The proposed adjustable notch filter network frequency for processing physiological signals is illustrated by drawings (hereinafter - adjustable notch filter) shown in Fig. 1-7, where

in fig. 1 shows a diagram - a prototype of the proposed device,

in fig. 2 - diagram of an adjustable notch filter,

in fig. 3 is a schematic diagram of an adjustable notch filter,

in fig. 4 shows graphs of the change in the amplitude of the input voltage depending on the given quality factor for an adjustable notch filter and a prototype circuit,

in fig. 5 - amplitude-frequency characteristics of the adjustable notch filter and the circuit of the prototype

in fig. 6 - amplitude-frequency characteristics of the adjustable notch filter in the region of suppression of the notch frequency at different quality factors.

in fig. 7 is a graph of the time dependence of the maximum input and output voltage of an adjustable notch filter for a given highest quality factor.

The adjustable notch filter in FIG. 2 contains: differential operational amplifier (1) (hereinafter referred to as DOU), potentiometer (2), original non-inverting notch filter (3), power supply common wire (4), resistive divider (5), limiting resistor (6), output amplifier ( 7). The inverting input of the DOU (1) is connected to the potentiometer slider (2), the first output of the potentiometer (2) is connected to the connection point of the output of the DOU (1) and the input of the original non-inverting notch filter (3), between the second output of the potentiometer (2) and the output of the original non-inverting notch filter (3) a limiting resistor (6) is connected, which together with the resistance of the potentiometer (2) forms a resistive voltage divider, a non-inverting notch filter (3) is connected to the common wire of the power source (4), between the input of the adjustable notch filter and the common wire of the power source (4) a resistive voltage divider (5) with a transfer coefficient Kdel is switched on, the output of which is connected to the non-inverting input of the differential operational amplifier (1). To the output of the original non-inverting notch filter (3), an amplifier (7) with a voltage gain of 1/Kdel is connected, the output of which is the output of an adjustable notch filter.

An increase in the quality factor Q of the filter is provided by moving the potentiometer slider towards the limiting resistance. In this case, the gain of the DOW increases.

To work in the linear zone of the DOW, a decrease in the input voltage supplied to the adjustable notch filter is required, since the voltage at the DOW output increases at the notch frequency, then a resistive voltage divider with a transfer coefficient Kdel is connected to the non-inverting input of the DOW.

The introduction of a resistive divider at the input of an adjustable notch filter with a division factor Kdel and the inclusion in series with the output of the original non-inverting filter of an amplifier with a gain of 1/Kdel makes it possible to operate the original non-inverting notch filter at a reduced input voltage by a factor of Kdel times and thereby provide an adjustable notch filter to the input maximum input voltage at the notch frequency, at the highest specified quality factor.

The technical result of the proposed adjustable network frequency notch filter for processing physiological signals is to ensure its operation at the maximum amplitude of the input voltage at the notch frequency and the maximum specified quality factor.

REFERENCES

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Claims (1)

Adjustable network frequency notch filter for processing physiological signals, containing a differential operational amplifier (1), the output of which is connected to the input of the original non-inverting notch filter (3), one output of which is connected to a common ground wire; potentiometer (2), the first output of which is connected to the output of the differential operational amplifier, the potentiometer slider (2) is connected to the inverting input of the differential operational amplifier (1), characterized in that between the second output of the potentiometer (2) and the output of the original non-inverting notch filter (3 ) limiting resistor (6) is on; between the input of the adjustable network frequency notch filter for processing physiological signals and the common wire of the power source (4), a resistive voltage divider (5) is connected, the output of which is connected to the non-inverting input of the differential operational amplifier (1), the output of the original non-inverting notch filter (3) is connected amplifier (7), the output of which is the output of an adjustable network frequency notch filter for processing physiological signals.

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