JPH05220121A - Automatic drift cancel circuit for portable electrocardiogram analyzer - Google Patents

Abstract

PURPOSE:To be hardly affected by archifact and to reduce erroneous analysis by executing DC bias to the input of a differential amplifier and following it up by a D/A converter so as to cancel fluctuation caused by archifact in the DC input to the differential amplifier. CONSTITUTION:This circuit is provided with a differential amplifier 1 to detect and amplify electrocardiogram signals led out of electrodes, DC bias circuit 2 to cancel the DC component of the differential input, and programmable low-pass filter 8 to extract a drift component. Further, an A/D converter 4 is provided to A/D convert the electrocardiogram signals, and a D/A converter 7 is provided to output a voltage value to the DC bias circuit from the obtained converted data. The drift component extracted by the low-pass filter 8 is inputted to the A/D converter 4 and based on the digital data, automatic drift cancel is executed by varying an output voltage V of the DC bias circuit by the D/A converter 7 so as to cancel the drift component.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrocardiogram input method for a portable electrocardiogram analyzer, and more particularly to an auto drift cancel circuit for a portable electrocardiogram analyzer.

[0002]

2. Description of the Related Art A conventional portable electrocardiogram analyzer has a differential amplifier in an electrocardiogram input section for detecting and amplifying a minute electrocardiogram signal derived from electrodes worn by a subject.
The electrocardiogram signal amplified about 5 times by this differential amplifier passes through the primary filter for cutting low frequency components (0.05HZ or less), and is amplified up to about 250 times by the main amplifier in the next stage. And was input to the A / D converter.

[0003]

The conventional portable electrocardiogram analysis device does not perform voltage conversion such as a DC-DC converter so as to withstand long-time use of 24 hours to 48 hours,
The conversion input range of the A / D converter 4 is 2 because it is driven directly by a battery (usually about 4 AA type batteries) and the device power supply voltage during operation varies from 6V to 4V. It is limited to about 0.5V. Therefore, if the gain is set to 250 times, the input range is ± 5 mV in terms of input, which is about half that of a normal electrocardiogram analyzer. Therefore, when the direct current input becomes excessive due to the body movement or the movement of the electrode pad, the input range of the A / D conversion is likely to be exceeded, which is a factor of erroneous analysis.

[0004]

An automatic drift canceling circuit of a portable electrocardiogram analyzer according to the present invention includes a differential amplifier for detecting and amplifying an electrocardiogram signal derived from an electrode attached to a subject, and the differential amplifier. Low-pass filter (LPF) for detecting a drift component from the output of the differential amplifier, a DC bias circuit that cancels the DC component of the differential input of the differential amplifier according to the output of the low-pass filter, and the A / D conversion of the electrocardiogram signal. A / D converter for
It comprises a D / A converter that outputs a bias voltage to the DC bias circuit from the conversion data obtained by the A / D converter.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. The output of the differential amplifier 1 that detects and amplifies the electrocardiogram signal derived from the electrodes attached to the subject is amplified by the main amplifier 3 to the input level of the A / D converter 4. Here, the signals e1 and e2 input to the inverting and non-inverting inputs of the differential amplifier are expressed by equations (1) and (2).

E1 = V1 + E1 (1) V1: electrocardiogram signal component E1: drift component due to polarization and artifacts e2 = V2 + E2 ... (2) V2: electrocardiogram signal component E2: drift component due to polarization and artifacts and bias When the output voltage of the circuit 2 is V, the output e0 of the differential amplifier 1 is represented by the equation (3).

E0 =-(R2 / R1) (V1-V2)-
(R2 / R1) (E1-E2) + V (3) In other words, since the second term of the equation (3) is considered to be the drift component to be canceled from the output of the differential amplifier 1, the third equation of the equation (3) is used. By changing the output voltage V of the bias circuit 2 of (4)
When the expression is satisfied, it becomes possible to cancel the drift.

V = R2 / R1 (E1-E2) (4) Therefore, the high-frequency cutoff frequency of the low-pass filter 8 is about 0.7 to 0.8 HZ (the same as the drift filter of an ordinary electrocardiograph). It becomes possible to extract the drift component of the electrocardiographic input waveform. The drift component extracted by the low-pass filter 8 is the A / D converter 4
Is input to the D / A converter 7, and the output voltage V of the DC bias circuit 2 is changed so as to cancel the drift component based on the digital data.

Further, by making the cut-off frequency of the low-pass filter 8 programmable, the low-frequency characteristics (cutoff frequency 0.0
It is also possible to realize 5HZ), so it is possible to reduce the number of primary high-pass filters used in ordinary electrocardiographic analyzers in order to satisfy the low frequency characteristics (cutoff frequency 0.05HZ). Becomes

The output of the A / D converter 4 is input to the D / A converter 7 via the arithmetic processing section 5 as described above, and is also stored in the memory 6 as an electrocardiogram signal. This electrocardiogram signal is taken out as needed and used for diagnosis or the like.

[0012]

As described above, according to the present invention, even if the direct current input to the differential amplifier fluctuates due to artifacts such as body movement, the input of the differential amplifier is DC biased so as to cancel the fluctuation. Since the output of the D / A converter follows up, it is less susceptible to the influence of artifacts and has the effect of reducing erroneous analysis.

Further, since the cutoff frequency of the low-pass filter is programmable and variable, the frequency characteristic of the high-pass filter (cutoff frequency 0.05 HZ) included in an ordinary electrocardiographic analyzer can be realized.
The primary filter circuit for cutting low frequency components can be eliminated, and the high-accuracy and large-capacity capacitor (for example, about 1 μF ± 5%) and high-accuracy and high-resistance (for example, 3. 6 MΩ ± 5%) can be reduced, which also has the effect of reducing the cost of parts and the mounting area.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

[Explanation of symbols]

 1 differential amplifier 2 direct current bias circuit 3 main amplifier 4 A / D converter 5 arithmetic processing unit 6 memory 7 D / A converter 8 programmable low-pass filter

Claims (2)

[Claims] 1. A differential amplifier that detects and amplifies an electrocardiogram signal derived from an electrode attached to a subject, a low-pass filter (LPF) for detecting a drift component from the output of the differential amplifier, and the low-pass filter. A DC bias circuit for canceling the DC component of the differential input of the differential amplifier according to the output of the filter, and the A / D signal for the electrocardiogram signal.
A portable electrocardiogram analysis characterized by comprising an A / D converter for conversion and a D / A converter for outputting a bias voltage to a DC bias circuit from the conversion data obtained by the A / D converter. Device auto-drift cancellation circuit. 2. A low-pass filter (LPF) is programmable in the portable electrocardiogram analyzer, whereby a primary filter for cutting low-frequency components can be deleted. An automatic drift cancellation circuit of the portable electrocardiogram analyzer described.