JPH0341689Y2 - - Google Patents

Description

[Detailed explanation of the idea] Industrial applications The present invention relates to a device for removing hum noise in biological signals.

BACKGROUND ART In conventional biological signal amplifiers, biological signals are disturbed by external induction noise, especially hum noise from commercial AC power sources, making it difficult to measure faithfully and accurately. For this reason, a 50 or 60 Hz band removal filter is generally used, but these filters also affect frequencies other than the removal frequency, resulting in distortion of the waveform of the input signal.

Problems to be solved by the invention Therefore, it is conceivable to eliminate only the hum noise so as not to affect the biological signals.

Means to solve the problem For this purpose, 50 or 60
One idea is to detect the phase and amplitude of the Hz hum noise and subtract a signal with the same phase and amplitude.

That is, the present invention includes an isolation transformer 6 for insulating commercial AC, a low-pass filter 7 for extracting the 50 or 60 Hz fundamental wave obtained from the transformer 6, and a phase detector 2 using a synchronous integrator synchronized with the commercial AC power supply.
and a hum level detector 3, and a phase shifter 8 which inputs only the fundamental wave from the low-pass filter 7 and which is controlled by the phase difference output of the phase detector 2 and generates a signal that matches the phase of the hum noise in the biological signal. , a variable gain amplifier 9 which is controlled by the hum level signal of the hum level detector 3 and obtains a signal having the same amplitude as the hum noise in the input signal;
a subtracter 1 for subtracting the hum noise canceling signal obtained from the phase shifter 8; a waveform shaper 4 for extracting a synchronizing signal from the 50 or 60 Hz signal obtained from the phase shifter 8 and controlling the phase detector 2 and the hum level detector 3; It is characterized by eliminating only hum noise in biological signals.

Function: In this way, it is possible to remove only the hum noise from a biosignal that includes hum noise without affecting the biosignal waveform.

Embodiment An embodiment of the present device will be described with reference to the drawings. FIG. 1 is a block diagram of the present device. 50 or 60Hz isolated from commercial power supply 5 through isolation transformer 6
From the signal, only the fundamental wave is extracted by a low-pass filter 7 and input to a phase shifter 8. Phase shifter 8 is 50 or 60
The phase of the Hz fundamental wave signal is controlled by the phase difference output of the phase detector 2 to match the phase of the hum noise in the biological signal. A signal in phase with the hum noise obtained from the phase shifter 8 enters a variable gain amplifier 9. The variable gain amplifier 9 makes the signal from the phase shifter 8 have the same amplitude as the hum noise in the control input signal using the hum level signal from the hum level detector 3. The cancellation signal from the variable gain amplifier 9 enters the subtracter 1 and is subtracted from the biological signal containing hum noise. In this way, only the hum noise in the biological signal is eliminated. The waveform shaper 4 converts the sine wave output of the phase shifter 8 into a square wave output, and controls the phase detector 2 and hum level detector 3.

Next, the operations of the phase detector 2 and the hum level detector 3 will be explained.

First, FIG. 2 shows an example of the circuit of the phase detector 2, and FIGS. 3 to 5 show signal waveforms of each part during its operation.
In Figure 3, the waveform A is the waveform of hum noise in the biological signal, and the biological signal is actually superimposed on it, but
It has been omitted. The waveforms B and C are synchronization signals for sampling obtained from the waveform shaper 4. d,
The waveform (e) is the waveform when the switch _S1 in FIG. 2 is opened and closed using the sampling synchronization signals (b) and (c). The waveforms B and C are synchronized with the phase of the signal from the phase shifter 8, that is, are in phase with the signal from the variable gain amplifier 9 that cancels hum noise. The waveform B is in phase with the waveform A, and the waveform C is 90 degrees behind the waveform A. FIG. 4 shows the change in the average value of the sample waveform with respect to the phase difference of the sampling synchronization signal with respect to the waveform A, which becomes 0 at -90 degrees. FIG. 5 shows the rate of change of the phase difference output of the phase detector 2 shown in FIG. 2 with respect to the phase difference, which becomes 0 at -90 degrees. The phase shifter 8 is controlled by the phase difference output of the phase detector 2, and when the phase difference is -90 degrees, the rate of change of the phase difference output of the phase detector 2 becomes 0, and the phase shifter 8
is locked. Since the hum noise voltage entering the phase detector 2 has been advanced in phase by 90 degrees, the signal obtained from the phase shifter 8 is in phase with the input hum noise. Moreover, the phase detector shown in FIG. 2 has a switch S ₁ ,
It operates as a synchronous adder with an integrator consisting of resistor _R1 , resistor _R2 , capacitor _C1 , operational amplifier _IC1 , and for biological signals that are not synchronized with the sampling synchronization signal, it adds the DC component. Since it does not contain any substances, it is averaged and does not react at all. As for hum noise, it is in a synchronous relationship with a synchronization signal created based on a commercial AC power supply, and an output is generated. In this way, only the phase of the hum noise superimposed on the biological signal can be detected.

Next, FIG. 6 shows an example of the circuit of the hum level detector 3, and FIGS. 7 and 8 show signal waveforms at various parts during its operation.
In Fig. 7, the waveform F is the waveform of hum noise in the biological signal, and the biological signal is actually superimposed on it, but
It has been omitted. The waveforms G and H are the output waveforms of the subtracter 5, the waveforms R are the synchronization signals for sampling obtained from the waveform shaper 4, and the waveforms R are the outputs of switch _S2 in Figure 6, which is opened and closed by the synchronization signals for sampling. This is the waveform when Figure 8 shows the change in the average value of the sampling waveform with respect to the change in the output of the subtractor 1 (the hum noise one cancellation signal), which becomes 0 when the hum noise and cancellation signal are equal, and the output change of the hum level detector 3. When the gain ratio becomes zero, the variable gain amplifier 9 controlled by the output of the hum level detector is locked and the amplitudes of the hum noise and the cancellation signal are kept equal. Also, the hum level detector shown in Figure 6 is a switch _S2 resistor.
It operates as a synchronous adder with an integrator consisting of R ₃ resistors R ₄ capacitors C ₁ operational amplifier IC ₂ , and for biological signals that are not synchronized with the sampling synchronization signal, it does not contain a DC component. Therefore, it is averaged and does not react at all. As for hum noise, it is in a synchronous relationship with the synchronization signal created based on the commercial AC power supply, and an output is generated. In this way, only the amplitude of the hum noise superimposed on the biological signal can be detected.

Effects of the invention In this way, by detecting the phase and amplitude of the hum noise included in the biosignal and subtracting it with a signal of the same phase and amplitude, only the hum noise is removed and the biosignal is added to the biosignal. could have no effect. Incidentally, it is also possible to omit the insulating transformer 6 and the low-pass filter 7 due to the circuit configuration.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the apparatus according to the present invention, FIG. 2 is a circuit example of the phase detector 2, and FIGS. 3 to 5 are signals and waveforms of various parts during its operation. Further, FIG. 6 shows an example of the circuit of the hum level detector 3, and FIGS. 7 and 8 show signal waveforms of various parts during its operation. In the figure, 1 is a subtracter, 2 is a phase detector, 3 is a hum level detector, 4 is a waveform shaper, 5 is a commercial power supply, and 6
is an isolation transformer, 7 is a low-pass filter, 8 is a phase shifter, and 9 is a variable gain amplifier.

Claims (1)

[Claims for Utility Model Registration] (1) An isolation transformer 6 that isolates commercial alternating current, a low-pass filter 7 that extracts the 50 or 60 Hz fundamental wave obtained from the transformer 6, and a synchronizer created based on the commercial alternating current power source. A phase detector 2 using a synchronous integrator that synchronizes with the signal, a hum level detector 3 that detects the hum level in the biosignal output, and a hum level detector 3 that receives only the fundamental wave from the low-pass filter 7 and the position of the phase detector 2. a phase shifter 8 which is controlled by a phase difference output and obtains a signal that matches the phase of hum noise in the biological signal; and a 50 or 60 Hz signal which is controlled by the hum level signal of the hum level detector 3 and obtained from the low pass filter 7.
a variable gain amplifier 9 which makes a signal whose fundamental wave matches the phase of the hum noise in the input biological signal by the phase shifter 8 with the same amplitude as the hum noise in the input signal; A subtracter 1 that subtracts the hum noise canceling signal obtained by the variable gain amplifier 9, and a waveform that extracts a synchronizing signal from the 50 or 60 Hz signal obtained from the phase shifter 8 and controls the phase detector 2 and hum level detector 3. 1. A hum noise removal device in a biological signal, comprising a shaper 4 and eliminating only hum noise in the biological signal. (2) The device for removing hum noise in a biological signal according to claim 1, which is a utility model, characterized in that a sine wave oscillator synchronized with a commercial power supply is used in place of the isolation transformer 6 and the low-pass filter 7. .