Signal detector

• US 5,891,048 A
• Filed: 06/18/1997
• Issued: 04/06/1999
• Est. Priority Date: 06/18/1996
• Status: Expired due to Term

• Current Assignee: Biotronik Mess-Und Therapiegeraete GmbH & Company Ingenieurbuero Berlin (Biotronik SE & Company KG)
• Original Assignee: Biotronik Mess-Und Therapiegeraete GmbH & Company Ingenieurbuero Berlin (Biotronik SE & Company KG)
• Inventors: Nigam, Indra B., Schaldach, Max
• Primary Examiner(s): Kamm, William E.
• Assistant Examiner(s): Evaniswo, George R.
• Application Number:
  US08/878,486
• Time in Patent Office: 657 Days
• Field of Search: 128/901, 128/902, 600/509, 600/517, 600/521, 607/4, 607/5, 607/9
• US Class Current: 600/521
• CPC Class Codes: A61N 1/3704 Circuits specially adapted therefor, e.g. for sensitivity control
• CPC Class Codes: Y10S 128/901 Suppression of noise in electric signal

Abstract

A signal detector for detecting a biosignal with approximately known morpogy in a complex input signal (ECG), in particular for the detection of QRS complexes in an electrocardiogram. The detector has circuitry for detecting the maximum amplitude (PEAK) of the detected signal complex within a predetermined time window, with a threshold value discriminator, a detector parameter preselection circuit for determining an initial value for the detector parameter characterizing the detector sensitivity, which parameter determines the detector threshold value when responding to a detection signal in dependence on the maximum amplitude and a detector parameter timing circuit for adjusting a predetermined time dependence of the detector parameter and thus the detection threshold value. The predetermined time dependence has at least in a first time domain a step-by-step reduction of the detection threshold value up to a lower limit value that is determined in dependence on the maximum amplitude and/or in a second time domain a step-by-step increase with preset steps (STEPS) up to an upper limit value determined in dependence on the maximum amplitude.

Claims

1. A signal detector for detecting a biosignal with nearly known morphology in a disturbed input signal (ECG) having signal complexes, comprising:

a detector input for detecting the input signal (ECG) with signal complexes and a detector output for emitting a detection signal that indicates the detection of the biosignal in the input signal;

a threshold value discriminator connected with the detector input, said threshold value discriminator comparing the input signal (ECG) with a detection threshold value and outputting to the detector output a high level signal so that the detector output emits the detection signal if the threshold value is exceeded by the input signal;

an amplitude detection device connected to the detector input and to the output of the threshold value discriminator and functions to detect a maximum amplitude of the detected signal complex during a predetermined time window, following the output of the detection signal;

an amplitude memory for storing the maximum amplitude of the detected signal complex, said amplitude memory being connected to the amplitude detection device and having several storage elements for storing a plurality of amplitudes of preceding signal complexes;

an arithmetic unit for calculating a variable lower limit value for the detection threshold value in dependence on the stored amplitudes, said arithmetic unit being connected to said amplitude memory and calculating the variable lower limit by giving a greater weight to the amplitudes of immediately preceding signal complexes than to amplitudes of older signal complexes;

a detector parameter pre-selection circuit that is connected to the arithmetic unit and to the threshold value discriminator, said detector parameter pre-selection circuit determining an initial value for a detector parameter which reflects the sensitivity of the signal detector, the detector parameter determines the detection threshold value by responding to the detection signal and in dependence on the maximum amplitude;

a detector parameter timing circuit connected to the threshold value discriminator for adjusting a predetermined time dependence of the detector parameter and thus also the detection threshold value, said detector parameter timing circuit starts with the initial value of the detector parameter, wherein the predetermined time dependence comprises in a first time domain a step-by-step reduction of the detection threshold value up to at most the lower limit value determined by the arithmetic unit.

2. A signal detector according to claim 1, further comprising a blocking element connected in series before the output, for blocking the emission of another detection signal during a predetermined time interval following a detection signal.

3. A signal detector according to claim 1, further comprising a time step memory assigned to the detection parameter pre-selection circuit, for storing at least one time dependence on the detection threshold value.

4. A signal detector according to claim 1, further comprising a threshold value memory and a second arithmetic unit which is connected to the threshold value memory for changing the detector parameter and thus the detection threshold by a predetermined factor.

5. A signal detector according to claim 1, further comprising an input amplifier having a control input for adjusting an amplification factor,

an amplitude classification memory for storing a classification threshold value, designed to differentiate between strong and weak detection events,;

and

a classification comparator unit connected to the amplitude classification memory and the detector input and indirectly with the input amplifier control input, said classification comparator unit comparing the input signal with the stored classification threshold value and producing a control signal at the input amplifier when the threshold value is exceeded.

6. A signal detector according to claim 1, further comprising a first detection threshold value limiter that is connected to an output of the arithmetic unit.

7. A signal detector according to claim 6, further comprising a second limiter connected in series with the first limiter for limiting the detection threshold value to a fixed predetermined, absolute limit value.

8. A signal detector according to claim 1, wherein the arithmetic unit calculates an upper limit value for the detection threshold value and the predetermined time dependence further comprises in a second time domain a step-by-step increase with predetermined steps of the detection threshold value up to at most the upper limit value determined by the arithmetic unit in dependence on the maximum amplitude of the immediately preceding signal complex.