Method and apparatus for suppressing power frequency common mode interference

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

a driving circuit configured to amplify and change the phase of a common mode interference signal to produce a first driving signal, wherein the common mode interference signal is extracted from a plurality of first electrodes attached to a patient;

phase compensating and processing circuitry electrically connected to the driving circuit for receiving the first driving signal, the phase compensating and processing circuitry configured to produce a second driving signal by phase-compensating the first driving signal based on a characteristic value of power frequency interference in a bioelectrical signal acquired through the plurality of first electrodes; and

a switch to receive the first driving signal and the second driving signal, the switch configured to selectively switch between providing the first driving signal and providing the second driving signal to a second electrode attached to the patient.

2. The apparatus of claim 1 , wherein the phase compensating and processing circuitry comprises:

at least one analog-to-digital (A/D) converter to convert the bioelectrical signal and the first driving signal from the driving circuit into respective digital signals;

a microprocessor to receive the digital signals and to determine a phase compensation amount of the first driving signal according to the characteristic value of the power frequency interference in the bioelectrical signal; and

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

3. The apparatus of claim 1 , further comprising:

a low-pass filter to filter the phase-compensated second driving signal.

4. A method for suppressing power frequency common mode interference in a bioelectrical signal measuring system, comprising:

receiving a common mode interference signal extracted from a plurality of first electrodes attached to a patient;

amplifying and changing the phase of the common mode interference signal to produce a first driving signal;

producing a second driving signal by phase-compensating the first driving signal based on a characteristic value of power frequency interference in a bioelectrical signal acquired through the plurality of first electrodes; and

selectively switching between providing the first driving signal and providing the second driving signal to a second electrode attached to the patient.

5. The method of claim 4 , wherein phase-compensating the first driving signal comprises:

initializing a system state value of a measuring system;

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

adding 1 to the system state value and extracting a second characteristic value;

if the second characteristic value has decreased from the first characteristic value, determining that the power frequency interference is reduced and that the direction of the compensation is correct, and continuing to step up the system state value and evaluating corresponding characteristic values until the system state value becomes maximized;

if the second characteristic value has increased from the first characteristic value, determining that the direction of the compensation is incorrect, subtracting 1 from the system state value, and selecting an optimum system state value, wherein the system state value is an integer and corresponds to one phase compensation state; and

setting the optimum system state value as a state value of the current system to determine a corresponding phase compensation amount.

6. The method of claim 5 , wherein the system state value ranges from [0, K], in which

K

=

int

⁡

(

f

s

200

)

-

1

,

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

7. The method of claim 5 , 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:

successively storing data of the bioelectrical signal sampled by an ND converter into a predetermined data array;

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

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; and

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

8. The method of claim 4 , further comprising performing a corresponding time delay processing on first driving signal by:

controlling an A/D converter using a microprocessor to set a sampling channel and a sampling frequency f s , and to sample the first driving signal outputted by the driving circuit;

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

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; and

converting the datum outputted at the sampling frequency f s into an analog signal by an D/A converter; wherein

K

=

int

⁡

(

f

s

200

)

-

1

,

int( ) denotes a rounding operation.

9. The method of claim 4 , further comprising providing the first driving signal outputted by the driving circuit to a delayer for performing a corresponding time delay processing, which is controlled by a microprocessor and whose delay time is adjustable.

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

driving means for amplifying and changing the phase of a common mode interference signal to produce a first driving signal, wherein the common mode interference signal is extracted from a plurality of first electrodes attached to a patient;

phase compensating and processing means electrically connected to the driving means for receiving the first driving signal, the phase compensating and processing means for producing a second driving signal by phase-compensating the first driving signal based on a characteristic value of power frequency interference in a bioelectrical signal acquired through the plurality of first electrodes; and

switching means for receiving the first driving signal and the second driving signal, the switch means for selectively switching between providing the first driving signal and providing the second driving signal to a second electrode attached to the patient.

11. The apparatus of claim 10 , wherein the phase compensating and processing means comprises:

first converting means for converting the bioelectrical signal and the first driving signal from the driving means into respective digital signals;

processing means for receiving the digital signals and to determine a phase compensation amount of the first driving signal according to the characteristic value of the power frequency interference in the bioelectrical signal; and

second converting means for receiving a signal from the microprocessor and converting the signal into an analog signal.

12. The apparatus of claim 10 , further comprising:

filtering means for filtering the phase-compensated second driving signal.