Method and apparatus for suppressing power frequency common mode interference

• US 20070087703A1
• Filed: 12/22/2005
• Published: 04/19/2007
• Est. Priority Date: 10/19/2005
• Status: Active Grant

• Current Assignee: Shenzhen Mindray Bio-Medical Electronics Co., Ltd. (Excelsior Union Ltd.), Shenzhen Mindray Scientific Co., Ltd.
• Original Assignee: Shenzhen Mindray Bio-Medical Electronics Co., Ltd. (Excelsior Union Ltd.)
• Inventors: Wu, Xiaoyu, Li, Shunan
• Granted Patent: US 7,684,853 B2
• Time in Patent Office: Days
• US Class Current: 455/114.200
• CPC Class Codes: A61B 5/30 Input circuits therefor

Abstract

A method and an apparatus for suppressing power frequency common mode interference which are used in a bioelectrical signal measuring system comprising a common mode interference signal extracting circuit and a driving circuit connected to the extracting circuit are provided. The driving circuit changes a phase of a common mode interference signal and amplifies the common mode interference signal, so as to output two-way amplified signals, wherein one amplified signal is selectively outputted to a living body on examination. In particular, the apparatus further includes phase compensating and processing means for receiving both a bioelectrical signal from the living body on examination and the other amplified signal outputted from the driving circuit, determining a phase compensation amount of the other amplified signal outputted from the driving circuit according to a characteristic value of the power frequency interference in the bioelectrical signal so as to phase-compensate the other amplified signal outputted from the driving circuit, and selectively outputting the phase-compensated amplified signal to the living body on examination. The method for suppressing power frequency common mode interference comprises the following steps of: receiving a bioelectrical signal from a living body on examination by phase compensating and processing means; analyzing the characteristic of the bioelectrical signal and determining a phase compensation amount by the phase compensating and processing means; performing a corresponding time delay processing on an amplified signal outputted by the driving circuit; and providing the delay signal to the living body on examination. According to this invention, the capability of the circuit for suppressing power frequency common mode interference is getting improved, and the stability of the analog circuit system and the phase-frequency characteristic of the circuit are maintained. This contributes to the improvement of the quality of the sampled bioelectrical signals.

Claims

1. An apparatus for suppressing power frequency common mode interference and used in a bioelectrical signal measuring system, comprising:

a common mode interference signal extracting circuit; and

a driving circuit connected to the extracting circuit, wherein the driving circuit changes a phase of a common mode interference signal and amplifies the common mode interference signal, so as to output two-way amplified signals, and one amplified signal is selectively outputted to a living body on examination, wherein

the apparatus further includes phase compensating and processing means for receiving both a bioelectrical signal from the living body on examination and the other amplified signal outputted from the driving circuit, determining a phase compensation amount of the other amplified signal outputted from the driving circuit according to a characteristic value of the power frequency interference in the bioelectrical signal so as to phase-compensate the other amplified signal outputted from the driving circuit, and selectively outputting the phase-compensated amplified signal to the living body on examination.

2. The apparatus for suppressing power frequency common mode interference as claimed in claim 1, wherein the phase compensating and processing means includes:

at least one A/D converter for converting the bioelectrical signal and the other amplified signal outputted from the driving circuit into digital signals respectively and supplying the digital signals to a microprocessor, which determines the phase compensation amount of the other amplified signal outputted from the driving circuit according to the characteristic value of the power frequency interference in the bioelectrical signal; and

a D/A converter for receiving a signal from the microprocessor and converting the signal into an analog signal.

3. The apparatus for suppressing power frequency common mode interference as claimed in claim 1, wherein the apparatus further includes a low-pass filter, through which the phase-compensated amplified signal outputted by the phase compensating and processing means passes before being transmitted to the living body on examination.

4. The apparatus for suppressing power frequency common mode interference as claimed in claim 1, wherein the apparatus further includes switching and selecting means with two selecting terminals, one of which is connected to an output terminal of the driving circuit, the other of which is connected to an output terminal of the phase compensating and processing means, and the switching and selecting means selectively outputs the amplified signal outputted by the driving circuit and the phase-compensated amplified signal outputted by the phase compensating and processing means to the living body on examination.

5. The apparatus for suppressing power frequency common mode interference as claimed in claim 3, wherein the apparatus further includes switching and selecting means with two selecting terminals, one of which is connected to an output terminal of the driving circuit, the other of which is connected to an output terminal of the low-pass filter, and the switching and selecting means selectively outputs the amplified signal outputted by the driving circuit and the phase-compensated amplified signal outputted by the phase compensating and processing means to the living body on examination.

6. A method for suppressing power frequency common mode interference, which is used for suppressing interference of power frequency common mode signal during a bioelectrical signal measuring system detects bioelectrical signals, wherein the measuring system comprises a common mode interference signal extracting circuit and a driving circuit connected to the extracting circuit for both changing phases of a common mode interference signal and amplifying the common mode interference signal, wherein the method includes steps of:

A. providing phase compensating and processing means between the driving circuit and a living body on examination;

B. receiving an amplified signal outputted from the driving circuit and a bioelectrical signal from the living body on examination by the phase compensating and processing means;

C. analyzing the characteristic of the bioelectrical signal and determining a phase compensation amount of the amplified signal outputted from the driving circuit by the phase compensating and processing means, wherein the characteristic of the bioelectrical signal is represented by a characteristic value of the power frequency interference in the bioelectrical signal;

D. performing a corresponding time delay processing on the amplified signal outputted by the driving circuit;

E. selectively transmitting the delay signal to the living body on examination.

7. The method for suppressing power frequency common mode interference as claimed in claim 6, wherein the step C includes steps of:

C1) initializing a system state value of the measuring system;

C2) extracting a characteristic value of the power frequency interference in a current system state of the measuring system;

C3) adding 1 to the system state value and extracting another characteristic value again;

C4) if the another characteristic value being decreased, it indicates the power frequency interference is reduced, thus the direction of the compensation is correct, then continuing the step C3) till the system state value becomes maximized;

otherwise, it indicates the direction of the compensation is incorrect, then subtracting 1 from the system state value, and then an optimum system state value is selected, wherein the system state value is integer and corresponds to one phase compensation state;

C5) setting the optimum system state value in the step 4) as a state value of the current system, to determine a corresponding phase compensation amount;

the above steps C1)˜

C5) are performed circularly.

8. The method for suppressing power frequency common mode interference as claimed in claim 7, wherein the system state value ranges from [0, K], in which

$K=\mathrm{int}$

( f s 200 ) - 1 ,

int( ) denotes rounding operation, and f_s denotes a sampling frequency of the bioelectrical signal.

9. The method for suppressing power frequency common mode interference as claimed in claim 7, wherein the characteristic value of the power frequency interference refers to a sum of peak to peak values of the power frequency interference signal extracted from the bioelectric signal within a plurality of periods, which is calculated by steps of:

a) successively storing data of the bioelectrical signal sampled by the A/D converter into a predetermined data array;

b) receiving the data array by a digital band-pass filter so as to extract the power frequency interference signal and output related data;

c) detecting a maximum value and a minimum value of the output data within a period, so as to calculate the peak to peak value of the signal within the period;

d) calculating a sum of the peak to peak values in a plurality of adjacent periods so as to get the characteristic value of the power frequency interference.

10. The method for suppressing power frequency common mode interference as claimed in claim 6, wherein the step D for performing a corresponding time delay processing on the amplified signal outputted by the driving circuit includes steps of:

D1) controlling the A/D converter by a microprocessor of the phase compensating and processing means, setting a sampling channel and a sampling frequency f_s, and sampling the amplified signal outputted by the driving circuit;

D2) creating a data array org_data[K+1], and successively storing amplified signal sampled by the A/D converter;

D3) determining a delay-output datum according to an optimum state value J of the current system, which corresponds an array element org_data[K−

J] of the data array;

D4) converting the datum outputted at the sampling frequency f_s into an analog signal by the D/A converter and then outputting the analog signal;

wherein

$K=\mathrm{int}<br><br>\left(\frac{f_s}{200}\right)-1,$

int ( ) denotes a rounding operation.

11. The method for suppressing power frequency common mode interference as claimed in claim 6, wherein in the step D the signal outputted by the driving circuit is transmitted to a delayer for performing a corresponding time delay processing, which is controlled by a microprocessor and whose delay time is adjustable.