Method and apparatus for the suppression of interference signals in a useful signal

• US 4,243,045 A
• Filed: 01/23/1979
• Issued: 01/06/1981
• Est. Priority Date: 02/10/1978
• Status: Expired due to Term

• Current Assignee: Siemens AG
• Original Assignee: Siemens AG
• Inventors: Maas, Michael
• Primary Examiner(s): Kamm, William E.
• Application Number:
  US06/005,865
• Time in Patent Office: 714 Days
• Field of Search: 128/696, 128/697, 128/710, 128/901, 128/419 PT, 128/698, 128/708
• US Class Current: 600/508
• CPC Class Codes: A61B 5/30 Input circuits therefor
• CPC Class Codes: A61B 5/308 for electrocardiography [ECG]
• CPC Class Codes: H03G 3/345 Muting during a short period of time when noise pulses are detected, i.e. blanking H03G3/348 takes precedence
• CPC Class Codes: Y10S 128/901 Suppression of noise in electric signal

Abstract

In an exemplary embodiment, the interference signals can occur as a mixture consisting of narrow interference pulse peaks of high amplitude and interference hum. It is desirable that such interference peaks and interference hum in a useful signal be suppressed without mutual influencing. To this end, an occurring useful signal having possibly superimposed interference signals is supplied to an interference hum filter. The filtered-out interference hum component is opposingly superimposed on the original signal for the purpose of compensation of the interference hum. This applies only for such a length of time as there are no interference pulse peaks recognized by a recognition installation. If such an interference pulse peak is recognized, the filter is disconnected from the input signal and switched over to self-oscillation operation. An artificial oscillation with an amplitude and frequency equal to that of the previously selected interference hum component is then generated without a phase jump and superimposed on the useful signal. The interference pulse peak is simultaneously blanked out. The exemplary embodiment can be particularly utilized in the case of electrocardiogram processing for the purpose of suppression of pacemaker pulses and power supply hum.

Claims

1. A method for suppressing noise signals in a useful signal, said method comprising the steps of:

(a) supplying an input signal comprising a useful signal (U1) which is subject to a noise hum signal (U_N) and to noise in the form of narrow noise pulses (P) of high amplitude which may be superimposed on the noise hum signal (U_N);

(b) monitoring said input signal to sense the presence of a narrow noise pulse (P);

(c) in the absence of the sensing of such a narrow noise pulse (P);

(c1) supplying the input signal to a noise hum filter (B1) to derive from the input signal a filtered-out interference hum component (U2) corresponding in waveform as a function of time to said noise hum signal (U_N); and

(c2) superimposing on the input signal in opposing relation said filtered-out interference hum component (U2) to tend to suppress the noise hum signal (U_N); and

(d) in the response to the sensing of such a narrow noise pulse (P) pursuant to step (b);

(d1) suppressing such narrow noise pulse;

(d2) decoupling the noise hum filter (B1) from the input signal, and switching over said noise hum filter (B1) to self-oscillation operation such that it continues to oscillate with the amplitude and frequency of the previously selected interference hum component without a phase jump to supply an artificially produced oscillation; and

(d3) superimposing on the input signal said artificially produced oscillation for the purpose of compensation of the interference hum during the period of supression of said narrow noise pulse.

2. A method according to claim 1 with said method further comprising suppressing the narrow noise pulse by blanking out of the input signal during a blanking-out time period, and responding to the sensing of a narrow noise pulse to store a directly preceding value of the useful signal for said blanking-out time period, and supplying the stored value of the useful signal as an initial value of a continuation of the useful signal.

3. A method according to claim 2 further comprising supplying the stored value of the useful signal as a control for the initial value of the self-oscillation operation of the noise hum filter (B1).

4. A method according to claim 2 further comprising delaying the input signal after suppression of the noise hum signal to provide a delayed signal (U6), and obtaining the stored value of the useful signal from the delayed signal.

5. A method according to claim 1 wherein the monitoring of the input signal to sense the presence of a narrow noise pulse takes place after the suppression of the noise hum signal so that a useful signal (U4) purified of the noise hum signal is monitored for the presence of a narrow noise pulse.

6. A method according to claim 1 wherein the suppression of the narrow noise pulse is effected during a blanking-out time period, and during such blanking-out time period generating a voltage waveform (U3) as a function of time corresponding to a waveform of an overshoot response to the narrow noise pulse, and superimposing said voltage waveform (U3) on the input signal to compensate for the overshoot response waveform therein.

7. A method according to claim 6 wherein the voltage waveform (U3) is generated in a time constant circuit (B5) having a time constant according to the time constant of the overshoot response waveform such that the resultant signal after compensation for the overshoot response simulates the input signal as it would have been transmitted in the absence of any noise hum signal and in the absence of the narrow noise pulse.

8. A method according to claim 6 further comprising generating said voltage waveform (U3) in a time constant circuit (B5) during the blanking-out time period such that the voltage value which corresponds to the peak value of the overshoot response waveform is held by the time constant circuit during the blanking-out time period and at the end of the blanking-out time period supplying the voltage waveform with a decaying characteristic corresponding to the decaying characteristic of the overshoot response waveform.

9. A method according to claim 6 further comprising adding the voltage waveform (U3) to the input signal (U) prior to supplying of the input signal to the noise hum filter (B1).

10. Apparatus for suppressing noise signals in a useful signal, said apparatus comprising:

(a) a measuring signal path having signal input means for supplying to the measuring signal path an input signal comprising a useful signal (U1) which is subject to a noise hum signal (U_N) and to noise in the form of narrow noise pulses (P) of high amplitude which may be superimposed on the noise hum signal (U_N), and having signal output means;

(b) monitoring means connected with said signal input means, and comprising an interference pulse peak recognition installation (B2) for monitoring the input signal to sense the presence of a narrow noise pulse (P);

(c) disconnect switch means (S1) connected with and controlled by said interference pulse peak recognition installation (B2) and maintained in a first condition thereby in the absence of the sensing of such a narrow noise pulse (P), but being shiftable to a second condition,

(c1) a noise hum filter (B1) operable for filtering out an interference hum component (U2) from the input signal, corresponding in waveform as a function of time to said noise hum signal (U_N), having filter input means connected with said signal input means under the control of said disconnect switch means (S1) such that in the absence of sensing of a narrow noise pulse (P) the disconnect switch means (S1) is in said first condition and supplies the input signal to said noise hum filter (B1) so that said noise hum filter (B1) derives from the input signal a filtered-out interference hum component (U2) corresponding in waveform as a function of time to said noise hum signal (U_N);

(c2) said noise hum filter (B1) having filter output means connected with said measuring signal path for superimposing on the input signal in opposing relation said filtered-out interference hum component (U2) to tend to suppress the noise hum signal (U_N),

(d) said interference pulse peak recognition installation (B2) being responsive to sensing of a narrow noise pulse (P) to actuate said disconnect switch means (S1) to said second condition,

(d1) said interference pulse peak recognition installation (B2) having output means connected with said measuring signal path for suppressing a narrow noise pulse at said signal output means in response to sensing of such narrow noise pulse by said interference pulse peak recognition installation (B2) pursuant to the monitoring of said input signal,

(d2) said disconnect switch means (S1) in said second condition decoupling the noise hum filter (B1) from said signal input means, and said noise hum filter (B1) having switchover means connected with and controlled by said interference pulse peak recognition installation (B2) and responsive to the sensing of a narrow noise pulse thereby to switch over said noise hum filter (B1) to self-oscillation operation such that it continues to oscillate with the amplitude and frequency of the previously selected interference hum component (U2) without a phase jump to supply an artificially produced oscillation; and

(d3) said filter output means of said noise hum filter (B1) during the suppression of a narrow noise pulse superimposing on the input signal said artificially produced oscillation for the purpose of compensation of the interference hum during the period of suppression of said narrow noise pulse.

11. Apparatus according to claim 10 with said noise hum filter (B1) being an active filter which is operated close to the transition from the damped to the undamped state, said switchover means comprising a feedback switch (S2) which is closed to operate said active filter in a self-excitation mode.

12. Apparatus according to claim 10, further comprising mixing means (A2) having a first input connected with said signal input means for receiving the useful signal (U1) which is subject to a noise hum signal (U_N), and having a second input and an output;

and

a time constant circuit (B5) connected with the second input of the mixing means (A2) for supplying thereto a compensation signal for compensating for the overshoot of a narrow noise pulse;

the output of said mixing means (A2) being connected via the disconnect switch means (S1) with the filter input means of the noise hum filter (B1).

13. Apparatus according to claim 10, with

said measuring signal path including mixing means (A1) having a first input connected with said signal input means for receiving a useful signal (U1) which is subject to a noise hum signal (U_N) and to noise in the form of narrow noise pulses (P), having a second input connected with said filter output means for receiving the filtered-out interference hum component, having a third input, and an output;

time constant circuit means (B5, S3, B4, A4) connected with said signal output means (U6) and with the output of said mixing means (A1) and operable for generating a compensation signal (U3) for compensating for an overshoot waveform portion of a narrow noise pulse, and connected with the third input of said mixing means (A1) for supplying the compensation signal (U3) thereto;

said interference pulse peak recognition installation (B2) being connected with the output of said mixing means (A1).

14. Apparatus according to claim 10, with

said disconnect switch means (S1) being interposed between the signal input means and the filter input means;

said switchover means comprising a feedback switch (S2);

said noise hum filter (B1) having a feedback circuit extending between said filter output means and said filter input means, said feedback circuit including said feedback switch (S2) and mixing means (A3) having a first input connected with the filter output means and having a second input; and

said measuring signal path including signal storage means (S4, B3) responsive to sensing of a narrow noise pulse (P) by said interference pulse peak installation (B2) to store a voltage value (U6) of the useful signal, said signal storage means (S4, B3) having an output connected with the second input of said mixing means (A3) and with said signal output means.

15. Apparatus according to claim 10 with time constant circuit means for forming a control path, and comprising an overshoot control switch (S3) connected with and controlled by said interference pulse peak recognition installation (B2) for assuming a closed condition when a narrow noise pulse (P) is sensed thereby, a time constant circuit (B5) having an input connected with said overshoot control switch (S3) and having an output connected with the filter input means under the control of said disconnect switch means (S1), and a comparator (B4) having input means (A4) connected with said signal output means (U6) and operable for sensing a peak value of an overshoot waveform portion of a narrow noise pulse, and having an output connected with the input of said time constant circuit (B5) under the control of said overshoot control switch (S3), said time constant circuit (B5) being responsive to closed condition of said overshoot control switch (S3) to rapidly charge to the peak value of the overshoot waveform portion.

16. Apparatus according to claim 15, with

the measuring signal path including first mixing means (A1) having a first input connected with said signal input means, having a second input connected with the filter output means, having a third input connected with the output of said time constant circuit (B5), and having an output,

said input means of said comparator (B4) comprising further mixing means (A4) having a first input connected with the output of said first mixing means (A1), having a second input connected with the signal output means (U6), and having an output connected with said comparator (B4) so that the comparator (B4) is connected with the signal output means (U6) via the further mixing means (A4);

and

said time constant circuit means being operable for supplying to the measuring signal path via said first mixing means (A1) a compensation signal (U3) for compensating for an overshoot waveform portion of the input signal following a narrow noise pulse, said further mixing means (A4), said comparator (B4) and said time constant circuit (B5) forming a closed control loop with the overshoot control switch (S3) in the closed condition for generating said compensation signal.

17. Apparatus according to claim 16 with said measuring signal path including signal storage means (S4, B3) connected with the output of the first mixing means (A1) for receiving and storing a signal (U4) purified of the noise hum signal (U_N), and having an output connected with the second input of said further mixing means (A4) supplying a stored signal thereto.