JPH0556942A - Direct-coupled electrocardiograph - Google Patents

Abstract

PURPOSE:To convert a living body signal to a signal which is scarcely fluctuated, and to fetch it as an electrocardiogram waveform which can be monitored easily and scarcely causes an analytic miss by providing a D/A converter for applying a fluctuation component of an input signal and a sample holding circuit in an inversion input of a correction amplifier. CONSTITUTION:When an input signal e1 is shifted large from a zero level of a base line due to a drift, etc., of a living body side, an output signal is not saturated, when an input range of a differential amplifier 1 is large enough. However, unless an input range of a main amplifier 2 is further widened, an output signal e2 is saturated. As an executable means for enlarging the input range, an analog signal e3 is selected by a multiplexer 3, subjected to A/D conversion, and thereafter, subjected to filtering processing by a data processing part and a base line fluctuation component of about DC-0.5Hz is extracted, and it is applied as a correction value e4 to the main amplifier 2 through a D/A converting part 6 and one piece of channel of a sample holding circuit 5. In such a way, a final correction output from which a fluctuation component of a low frequency is eliminated can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct-coupled electrocardiograph, and more particularly to a direct-coupled electrocardiograph with baseline fluctuation corrected.

[0002]

2. Description of the Related Art A conventional electrocardiograph amplifier includes a series capacitor C for cutting a component of 0.05 Hz or less between a differential amplifier 1 at a preceding stage and a main amplifier 2 as shown in FIG. On the other hand, it has an instrument switch ISW for discharging the electric charge of the capacitor C in a short time. Since the frequency band of the electrocardiographic signal is in the low frequency range of DC to 100 Hz and the time constant of CR needs to be set to a large value such as 3.2 seconds, the resistance R also increases to several MΩ and the bias A high input impedance main amplifier 2 with a sufficiently small current is used.

[0003]

In the conventional electrocardiograph, in order to prevent the amplifier from being saturated by the fluctuation of the low frequency component due to the polarization voltage or body movement generated in the living body, the input amplifier 11 in the preceding stage, A CR element having a large value is inserted between the main amplifier 12 in the next stage and the main amplifier 12 is operated as an AC amplifier in which a low frequency component of 0.05 Hz or less is cut.

Since it takes 6 seconds or more for the output signal level to return to the base line position in response to a sudden change in the input signal due to an artifact (disturbance), the instrument switch ISW is forcibly turned on. , The high impedance input resistor 8 is short-circuited, the residual charge of the capacitor C is rapidly discharged, and the output waveform is returned to the baseline level. While the instrument switch ISW is on, the electrocardiographic waveform is not output and cannot be observed. Further, the fluctuation of 0.05 Hz to several Hz is output as it is, and there is a problem that the output is saturated for a large fluctuation exceeding the input range of the main amplifier. Furthermore, the input fluctuation range is large, 200 m
In the case of continuing for more than s, even if the instrument switch ISW is turned on, it does not completely return to the zero level,
There was a problem that the base line fluctuates with a time constant of CR (= 3.2 seconds).

[0005]

A direct-coupled electrocardiograph according to the present invention comprises a differential amplifier at a front stage for inputting an electrocardiogram signal, a main amplifier for correction for canceling a fluctuation component of the output of the differential amplifier, and A multiplexer that selects the output of the main amplifier and sends it to the A / D converter; an A / D converter that converts the output of the multiplexer into digital data;
A data processing unit for calculating the data digitized by the converter, a D / A converter for outputting the correction data processed by the processing unit, and this output are applied to the inverting input of the correction main amplifier of 8CH, respectively. And a sample hold circuit.

[0006]

The present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention.
The state of the operation waveform at each point is shown in FIG. The input signal e1 is
When a shift from the zero level of the baseline to a large positive or negative direction is caused by a living body side drift or some artifact, the fluctuation of the output e2 of the differential amplifier 1 of the preceding stage having the amplification degree A1 is changed by being multiplied by A1. If the input range of the previous stage is large enough, the output signal will not be saturated,
If the input dynamic range of the second-stage main amplifier 2 is further widened, the output signal e2 will be saturated immediately. As a means for practically expanding the input dynamic range, a signal equivalent to a low frequency drift component is input to the inverting input of the second stage amplifier 2. The analog signal e3 is selected by the multiplexer 3 and, after A / D conversion, filtering processing is performed by the data processing unit to extract a baseline fluctuation component of about DC to 0.5 Hz, and the result is used as a correction value e4 for D / A.
It is applied to the main amplifier 2 via one channel of the conversion unit 6 and the sample and hold 5 to obtain the final corrected output from which the low frequency fluctuation component is removed. At this time, the data processing unit is 0.5
It consists of a digital filter that is executed within ms.

The sample-hold circuit comprises an 8-channel hold capacitor Cd, sample / hold switches SW1 to SW8, and a decoder for on / off controlling these switches, and the outputs of the D / A converters 6 are respectively provided. Are distributed over the channels.

[0009]

As described above, according to the present invention, the D / s for applying the fluctuation component in the vicinity of DC to 0.5 Hz of the input signal to the inverting input of the correction amplification 2 at the rear stage of the front stage differential amplifier 1.
Since the A converter, the sample and hold circuit, and the data processing unit 7 have a digital filter for extracting only the low-frequency component, a biological signal including a polarization component such as an electrocardiogram waveform and a drift component of the baseline fluctuation can be obtained. It has an effect that it can be converted into a signal with little fluctuation and can be extracted as an electrocardiographic waveform that is easy to monitor and has few analysis errors. Further, a large-capacity capacitor for cutting DC component between the differential amplifier 1 in the previous stage and the main amplifier 2 for correction in the second stage and an input having a time constant of 3.2 seconds or more in combination with this capacitor Since there is no resistance, the time until the waveform stabilizes at the baseline level against an abrupt change is instantaneously (= 4 ms), and the instrument switch ISW for discharging the charge stored in the capacitor is no longer required, and the input section Since it is not necessary to use a high impedance amplifier,
It is not necessary to consider the leak of the board surface and the leak of the component element, and the assembly is easy. Further, since the signal does not directly pass through the coupling capacitor, there is an effect that waveform distortion due to the element does not occur.

[Brief description of drawings]

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

FIG. 2 is a waveform diagram showing signal waveforms of respective parts of the block diagram shown in FIG.

FIG. 3 is a circuit diagram showing an outline of an electrocardiograph amplifier according to a conventional technique.

[Explanation of symbols]

 1 differential amplifier 2 main amplifier 3 multiplexer 4 A / D converter 5 sample and hold circuit 6 D / A converter 7 data processing unit

Claims (1)

[Claims] 1. A first-stage differential amplifier for inputting an electrocardiogram signal, a main amplifier for correction for canceling a fluctuation component of the output of the differential amplifier, and an output of the main amplifier are selected to an A / D converter. A multiplexer for sending, an A / D converter for converting the output of the multiplexer into digital data,
A data processing unit for calculating data digitized by the A / D converter, a D / A converter for outputting correction data processed by the processing unit, and an output of the D / A converter for inverting a main correction amplifier of 8CH. A direct-connection type electrocardiograph comprising a sample-hold circuit for applying to an input.