Device for eliminating ringing in filtered ECG signals

• US 5,532,951 A
• Filed: 06/27/1994
• Issued: 07/02/1996
• Est. Priority Date: 07/16/1993
• Status: Expired due to Fees

• Current Assignee: Siemens-Elema AB (Siemens AG)
• Original Assignee: Siemens-Elema AB (Siemens AG)
• Inventors: Karlsson, Peter, Ohlsson, Thomas
• Primary Examiner(s): Malzahn, David H.
• Application Number:
  US08/266,233
• Time in Patent Office: 736 Days
• Field of Search: 364/724.17, 364/724.01, 364/413.06, 128/696
• US Class Current: 708/320
• CPC Class Codes: A61B 5/30 Input circuits therefor

Abstract

A device for eliminating ringing in filtered ECG signals includes an analog-to-digital for converting the ECG input signals into a series of digital values, and a filter unit connected to the output of the analog-to digital converter. The filter unit includes a recursive IIR-filter and a subsequent allpass filter with a phase shift which is equal to twice the phase shift of the IIR filter. The allpass filtering is performed time-reversed with respect to the IIR filtering. In a method for producing an allpass filter, for use in the above device, having a phase shift which is equal to twice the phase shift of an IIR filter, the IIR filter having zero points situated on the unity circle in the Z-plane, the zero points of the IIR filter are replaced by new zero points obtained by reflecting the poles of the filter in the unity circle in the Z-plane.

Claims

1. A device for eliminating filter-produced ringing in filtered ECG signals comprising:

an analog-to-digital converter to which analog ECG signals are supplied, said converter converting said analog ECG signals into a series of digital values;

a recursive IIR filter to which said digital values are supplied, said recursive IIR filter filtering said digital values and generating an output signal exhibiting a phase shift and simultaneously introducing ringing into said output signal; and

an allpass filter supplied with said output signal of said recursive IIR filter, said allpass filter filtering at least a portion of said output signal from said IR filter time-reversed in comparison to said IIR filter and with a phase shift equal to twice the phase shift exhibited by the output signal from the IIR filter to eliminate said ringing.

3. A device as claimed in claim 1 wherein each of said ECG signals contains a QRS complex, and wherein said allpass filter comprises means for only filtering a latter part of each QRS complex.

4. A device as claimed in claim 1 wherein said ECG signals each contain a QRS complex, and wherein said allpass filter comprises means for only filtering an earlier part of each QRS complex.

2. A device for eliminating filter-produced ringing in filtered EGG signals comprising:

an analog-to-digital converter to which analog EGG signals are supplied, said ECG signals each containing a QRS complex;

an averager supplied with said digital values, said averager forming a signal average over a number of said QRS complexes;

a recursive IIR filter to which said signal average is supplied, said recursive IIR filter filtering said signal average and generating an output signal exhibiting a phase shift and simultaneously introducing ringing into said output signal; and

an allpass filter supplied with said output signal of said recursive IIR filter, said allpass filter filtering at least a portion of said output signal from said IIR filter time-reversed in comparison to said IIR filter and with a phase shift equal to twice the phase shift exhibited by the output signal from the IIR filter to eliminate said ringing.

5. A method for producing an allpass filter having a phase shift which is equal to twice the phase shift of an IIR filter having poles and having zero points situated on a unity circle in the Z-plane, comprising the steps of:

reflecting the poles of the IIR filter in the unity circle in the Z-plane to obtain new zero points; and

replacing the zero points of said IIR filter with said new zero points.