JP3079330B2 - High-pass filter for impulse - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an impulse high-pass filter for extracting minute high-frequency components immediately after an impulse such as a QRS wave of an electrocardiogram.

[0002]

2. Description of the Related Art As shown in FIG. 6, in a QRS wave of an electrocardiogram, a rate potential 1 having a small amplitude of a high frequency component (shown in an enlarged manner in the figure) is an S wave depending on a subject depending on a subject. And between the T-waves. that time,
If an attempt is made to extract with a high-pass filter using a normal CR circuit having a cutoff frequency of about 50 Hz for the monitoring, detection may be difficult due to the continuous oscillation of the filter output signal of the QRS wave. Considering the cause for the step input response, the base line return time is delayed, and the amplitude of the tail portion is larger than the minute signal level. Even if a high-pass filter is replaced by a second-order or third-order CR circuit, it has not been fundamentally solved.

[0003]

SUMMARY OF THE INVENTION In view of the foregoing, an object of the present invention is to provide an impulse signal of the kind described at the beginning which can recover the trailing edge of the impulse sharply by an analog circuit using a resistor, a capacitor, and the like. An object is to provide a high-pass filter.

[0004]

In order to achieve this object, the present invention provides an input high-pass filter comprising a CR differentiating circuit to which an impulse is input and which has a cut-off frequency higher than a required cut-off frequency. A compensation signal corresponding to the amplitude difference between the step response characteristic of the input high-pass filter and the target step response characteristic which starts with the slope of the step response characteristic of a low cut-off frequency and halves the elapsed time to substantially zero level is generated. A compensation signal generation circuit; an addition circuit for adding the output signal of the input high-pass filter and the compensation signal; the compensation signal generation circuit including a first integration circuit that receives the output signal of the input high-pass filter as an input; A second integration circuit that integrates an output signal of the integration circuit, and an output signal of the second integration circuit is integrated by an integration capacitor of the first integration circuit. The compensation signal is fed back to the terminal opposite to the input terminal of the first integration circuit by adjusting the amplitudes of the output signals of the first and second integration circuits and subtracting the output signal of the second integration circuit from the output signal of the first integration circuit. Is generated.

[0005]

When the input impulse passes through the input high-pass filter, the components near the cut-off frequency are also excessively cut in accordance with the cut-off frequency characteristic higher than the required cut-off frequency characteristic. During this time, in the compensation signal generating circuit, the low frequency component in the cutoff region side with respect to the cutoff frequency is generated with a relatively large amplitude by the integration of the output signal of the first integration circuit in the second integration circuit. The output signal of the first integrating circuit is
Is output to the opposite side of the integration capacitor of the first integration circuit, and the component on the transmission band side with respect to the cutoff frequency is increased. As a result, the amplitudes of these integrated outputs are adjusted, and the cut-off frequency region is compensated for by the output of the first integrating circuit, and the characteristics on the transmission band side near the cut-off frequency are complemented so as to be steep. A compensation signal for reducing components in the cutoff region is generated by the output signal of the second integration circuit. As a result, the high-pass filter exhibits almost the target step response characteristic, and therefore, an impulse output that is low-cut and quickly returns to the baseline can be obtained.

[0006]

FIG. 1 shows a cutoff frequency 5 according to an embodiment of the present invention.
It shows a high-pass filter for 0 Hz impulse,
An input high-pass filter 1 comprising a first-order differentiating circuit;
A first integration circuit 2, a second integration circuit 3, an amplitude adjustment circuit 4 for reducing the amplitude of the output signal to 1/4, and an adder for adding the output signal of the input high-pass filter 1 and the compensation signal A5.

FIG. 2 shows a detailed circuit of the circuit.
1 and the capacitor C1 are an input high-pass filter 1 composed of a CR (capacitor and resistor) first-order differentiating circuit having a time constant (1.6 ms) corresponding to 100 Hz which is twice the cut-off frequency required for the high-pass filter of 50 Hz. Constitute. A1 to A3 are buffer amplifiers. The resistor R2 and the capacitor C2 constitute a first integrating circuit 2, and the resistor R3 and the capacitor C3 constitute a second integrating circuit 3. The second integrating circuit 3 is connected to a terminal opposite to the input of the capacitor C2 as an integrating capacitor through a buffer amplifier A2. The output signal of the integration circuit 3 is fed back. These first and second integrating circuits 2 and 3 constitute a so-called feedback low-pass filter. The output signal of this low-pass filter is set to a cutoff frequency of about 53 Hz, and the shoulder characteristic is set by Q = (C2 / 2C3) ^1/2 = 0.5 (where C2 and C3 are the associated capacitor capacitance values in this equation). Have been. At this time, the first integration circuit 3 exhibits a primary low-pass filter characteristic of the same cutoff frequency. The buffer amplifier A3 supplies the output voltage B of the first integration circuit 2 to the adder A5, and the amplifier A4 adjusts the output voltage C of the second integration circuit 3 to 1/4 in amplitude and supplies it to the adder A5. I do.

As shown in FIG. 3, the first and second integration circuits 2 and 3 first start with a slope characteristic Db of a normal step response characteristic Da having a required cutoff frequency of 50 Hz, and are 1% or less of the maximum value. Of the step response characteristic Da is assumed to be half of the elapsed time to reach the substantially zero level of the step response characteristic Da. The cutoff frequency 1 for the target step response characteristic
A compensation signal E corresponding to the amplitude difference (indicated by hatching) of the step response characteristic A of the input high-pass filter 1 of 00 Hz is generated.

That is, in the step response characteristic A of the input high-pass filter 1, a component near 50 Hz is reduced with respect to the target step response characteristic D so as to enable compensation by addition. The compensation signal E complements the reduced component and performs compensation to approach the target step response characteristic D. When the feedback amount is zero, the output voltages of the first and second integration circuits 2 and 3 become like dotted lines, respectively, and the amplitude of the tail portion of the output voltage of the second integration circuit 3 increases by the second integration. The output voltage B of the first integration circuit 2 shown by the solid line generates a compensation signal in a hatched area, and the slope characteristic D by feedback.
The region inside b, that is, the region within the time constant CR (1.6 ms) is more compensated. Similarly, the output voltage C of the second integration circuit 3 indicated by the solid line becomes a waveform Co whose amplitude is adjusted to １ ／ and whose polarity is inverted, and further becomes a compensation signal E by addition with the output voltage B, and becomes a step signal. Response characteristics A
Around 1% of the amplitude, ie, the tail portion, is effectively compensated.

In other words, as shown in FIG. 5A, the output voltage B approaches the characteristic of the cutoff frequency of 100 Hz to 50 Hz, and the hatching region (the cutoff frequency of 50 Hz). The output voltage C is mainly 6d in the dot area (attenuation area side with respect to cutoff frequency of 50 Hz).
By compensating for closer to B / oct, a high-pass filter characteristic having an improved shoulder characteristic with respect to a cutoff frequency of 50 Hz can be obtained as shown by a dotted line. Further, a constant delay characteristic near a cutoff frequency of 50 Hz, that is, a phase rotation characteristic proportional to the frequency can be obtained in a wider range.

When the input impulse is added with the compensation signal E, the cut-off frequency 50 Hz region is cut beforehand when passing through the high-pass filter 1 so as to prevent components in the cut-off frequency 50 Hz region from being excessively compensated. In this case, the cut-off frequency region is sharply compensated during the compensation. In order to confirm the impulse response characteristics, a response to a triangular wave having a time width of 100 ms as shown in FIG. 4A is normally confirmed. A normal high-pass filter having a cut-off frequency of 50 Hz of a CR has a response waveform indicated by a dotted line in FIG. 4B. In contrast, the high-pass filter of the present invention is improved as shown by the solid line. This triangular wave can be considered to be similar to the QRS wave of the electrocardiogram, and is also effective for detecting a minute high frequency component generated immediately thereafter.

FIG. 7 shows an embodiment provided with an input high-pass filter constituted by a secondary CR differentiating circuit, which comprises a capacitor C11 having constants as shown, resistors R11 and C12, and a resistor R12. Amplifier A11 following the secondary input high-pass filter 11
, Followed by first and second integrating circuits. In this high-pass filter, the asymptote of the attenuation characteristic has a quadratic 12 dB /
oct, and the shoulder area to be compensated is a cutoff frequency of 50 Hz.
Accordingly, the cut-off frequency is set to twice to about 1.7 times the required cut-off frequency of 50 Hz for the above-described embodiment. The resistors R13 and R14, the buffer amplifier A12, and the capacitor C13 form a first integrating circuit, and the resistor R15 and the capacitor C14 form a second integrating circuit. The resistors R16 and R17 form a 1/2 amplitude adjustment circuit. The second integrated output is provided to the adder A13-input terminal, the first integrated output is provided to the + input terminal from the resistor R13, and the output of the input high-pass filter 11 is provided as R
14 is input.

In order to form a compensation signal generating circuit with such first and second integrating circuits, as shown in FIG. 8, the target step response characteristic D is 37% of the step response characteristic Da at a cutoff frequency of 50 Hz. It is assumed that it descends to the (1 / e) level with the same inclination characteristics as the first, and reaches zero level in half the elapsed time of the normal after it is once transferred to minus. A compensation signal E corresponding to an amplitude difference (indicated by hatching) of a step response characteristic A of the input high-pass filter 11 with respect to the target step response characteristic D is generated.

That is, in FIG. 8, the output voltages B and C of the first and second integration circuits 2 and 3 are obtained as shown by the solid line with no feedback shown by the dotted line with feedback added to the characteristics. That is, the output voltage B compensates the step response characteristic A so as to approach the linear region of the target step response characteristic D. The output voltage C has a relatively large outer component, the amplitude of which is adjusted to 、, the polarity is inverted, and the waveform Co is obtained.
Is compensated to return to the point of return to zero. In other words, FIG.
As shown in B, the characteristic of the output voltage B, which is excessively cut off in the vicinity of the cut-off frequency, approaches the characteristic of the cut-off frequency of 50 Hz, as well as the normal attenuation characteristic of the cut-off frequency of 50 Hz shown by the solid line. Frequency 50H
z in the transmission band), and compensates for the output voltage C so that the attenuation region side mainly represented by the dots becomes closer to 12 dB / oct, so that the shoulder characteristic of the cutoff frequency 50 Hz is obtained as shown by the dotted line. An improved high-pass filter characteristic is obtained. For a triangular wave, a response waveform as shown in FIG. 4C is obtained, which is improved from a dotted waveform as shown by a solid line.

Further, by connecting the above-mentioned primary high-pass filter and secondary high-pass filter in series,
A third-order high-pass filter can be configured. In this case, as shown in FIG. 5C, the asymptote of the attenuation characteristic is 18 dB.
Similarly, for the frequency characteristic of / oct, the output voltage of the first integration circuit compensates for the entire characteristic and the hatched area, and the output voltage of the second integration circuit compensates for the dot area. Characteristics are obtained. The response waveform for the triangular wave is shown in FIG. 4D.

The present invention is applicable not only to the QRS wave but also to a case where a high-frequency component generated immediately after an impulse is extracted. The secondary high-pass filter can also be configured by connecting the above-mentioned primary high-pass filter in series, and the tertiary high-pass filter should be configured by tertiary input high-pass filter and also with a corresponding compensation circuit attached. Can also.

[0017]

As described above, the impulse high-pass filter using the simple analog circuit using the resistor and the capacitor according to the present invention makes it possible to eliminate the phase transition in the cut-off frequency region of the high-pass filter and to sharpen the shoulder characteristic of the amplitude. Becomes In other words, the return of the base line after passing through the high-pass filter to the impulse whose main component is the cutoff frequency region is accelerated. A minute high-frequency component such as LP generated immediately after the QRS wave can also be extracted. By increasing the order of the high-pass filter to the second and third order, a steeper low-frequency attenuation characteristic is realized, and the impulse response characteristic is further improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a basic configuration of an electrocardiogram signal high-pass filter according to an embodiment of the present invention.

FIG. 2 is a diagram showing a detailed circuit of the high-pass filter.

FIG. 3 is a diagram illustrating the operation of the high-pass filter.

FIG. 4 is a diagram for explaining a response characteristic of the high-pass filter according to FIGS. 1 and 7;

FIG. 5 is a diagram showing a frequency characteristic of the high-pass filter according to FIGS. 1 and 7;

FIG. 6 is a waveform diagram of an electrocardiogram which is an input signal of a high-pass filter according to the present invention.

FIG. 7 is a diagram showing a configuration of an impulse high-pass filter according to another embodiment of the present invention.

FIG. 8 is a diagram illustrating the operation of a high-pass filter according to another embodiment.

[Explanation of symbols]

 1,11 High-pass filter for input

Claims (1)

(57) [Claims] 1. An input high-pass filter comprising a CR differentiating circuit to which an impulse is input and having a cut-off frequency higher than a required cut-off frequency, and a slope of a step response characteristic of a necessary cut-off frequency, and substantially starts. A compensation signal generating circuit for generating a compensation signal corresponding to an amplitude difference of a step response characteristic of an input high-pass filter with respect to a target step response characteristic in which an elapsed time to reach zero level is reduced, an output signal of the input high-pass filter and the compensation A compensating signal generating circuit, wherein the compensation signal generating circuit receives the output signal of the input high-pass filter as an input, and integrates the output signal of the integrating circuit. And an output signal of the second integration circuit is connected to an input terminal of the first integration circuit opposite to an input terminal of the integration capacitor. And adjusting the amplitude of the output signals of the first and second integration circuits and subtracting the output signal of the second integration circuit from the output signal of the first integration circuit to generate the compensation signal. Characteristic high-pass filter for impulse.