Installation for the detection and processing of electrical signals

• US 3,968,430 A
• Filed: 12/06/1974
• Issued: 07/06/1976
• Est. Priority Date: 12/13/1973
• Status: Expired due to Term

• Current Assignee: Siemens AG
• Original Assignee: Siemens AG
• Inventors: Maas, Michael
• Primary Examiner(s): Rolinec, R. V.
• Assistant Examiner(s): Tokar, Michael J.
• Application Number:
  US05/530,354
• Time in Patent Office: 578 Days
• Field of Search: 324/77 B, 324/77 D, 324/77 E, 324/77 F, 324/78 E, 324/78 F, 324/78 Z, 128/2.05 P, 128/2.05 R, 128/2.05 T, 128/2.06 A, 128/2.06 B, 128/2.06 E, 128/2.06 F, 128/2.06 R
• US Class Current: 600/521
• CPC Class Codes: A61B 5/30 Input circuits therefor
• CPC Class Codes: A61B 5/308 for electrocardiography [ECG]
• CPC Class Codes: G01R 13/04 for producing permanent records
• CPC Class Codes: H03G 5/165 Equalizers; Volume or gain control in limited frequency bands
• CPC Class Codes: H03G 5/18 in untuned amplifiers
• CPC Class Codes: Y10S 128/901 Suppression of noise in electric signal

Abstract

An installation for the detection and, respectively, processing of electrical signals, in particular, physiological measuring signals, for example EKG, through the intermediary of a filter arrangement located in the measuring signal channel which is determinative of desired frequency components of the signals. The filter arrangement encompasses controllable means for the variation of the frequency range, as well as for the damping of the transmitted signal components; and which provides a control installation for effecting the control of the controllable means in dependence of the signal amplitudes in the sense whereby the transmission frequencies of the filter arrangement at signals with, in the normal case, relatively high or in contrast therewith still higher signal amplitude components, at an increase of the transmission damping, may be displaced in the direction of frequencies which are essentially significant for these high signal amplitude components; and for signals with abnormally low signal amplitude components, at a reduction of the transmission damping, may be displaced in the direction of frequencies which are essentially significant for these low signal amplitude components.

Claims

1. In an installation for the detection and processing of electrical signals, in particular physiological measuring signals such as EKG, including a filter arrangement located in the measuring signal channel which is determinative of the desired frequency components of the signals;

and a threshold discriminator for the filter output signals, the improvement comprising;

said filter arrangement including a voltage divider having a voltage-controlled variable resistance, said voltage divider forming control means for varying the frequency range and the filter damping of passed-through signal components;

a control voltage generator, said control voltage generator generating a control signal at signal amplitudes above the threshold of said threshold discriminator for displacing the variable resistance in the voltage divider of said filter arrangement so that the signal components previously lying above the threshold of said threshold discriminator are damped below the threshold by said voltage divider while the frequency range of said filter arrangement is concurrently displaced to higher frequencies, and at signal amplitudes lying continually below the threshold of said threshold discriminator the control signal of said control voltage generator disappears whereby, with the disappearance of said control signal, said filter arrangement is controlled to lower degrees of transmission damping through the variable resistance of said voltage divider for raising the lower signal components in a direction towards the threshold of said threshold discriminator while concurrently displacing the frequency range of said filter arrangement towards lower frequencies.

2. Installation as claimed in claim 1, said filter arrangement and said controllable voltage divider being constructed for narrowing the transmission frequencies of said filter arrangement at high signal ampliitude components above the threshold of said threshold discriminator to frequencies essentially significant to said high signal amplitude components, and for widening said transmission frequencies at low signal amplitude components below the threshold of said threshold discriminator to frequencies essentially significant to said low signal amplitude components.

3. Installation as claimed in claim 1, said filter arrangement and said controllable voltage divider being constructed to effect controls for raising the transmission damping of said filter arrangement to a maximum value at said high signal amplitude components above the threshold of said threshold discriminator, and for reducing the transmission damping to a minimum value at said low signal amplitude components below the threshold of said threshold discriminator.

4. Installation as claimed in claim 3, said controllable voltage divider correlating the maximum value and minimum value of the transmission damping with each other so that the amplitude value of said high signal component damped with the maximum value corresponds to the amplitude value of the said signal component damped with the minimum value.

5. Installation as claimed in claim 1, said filter arrangement having a minimum value for the transmission damping selected so that the low signal components after transmission through said filter arrangements have the amplitude thereof located essentially closely below the threshold of said threshold discriminator.

6. Installation as claimed in claim 1, said voltage-controlled variable resistance being built into said voltage divider so that a reduction in the resistance value of the latter effects an increase in the dividing ratio of the voltage divider with a concurrent increase in the lower limit frequency of a high-pass filter in said filter arrangement, and an increase in the resistance value effects a reduction in the dividing ratio of the voltage divider with a concurrent reduction in the lower limit frequency of said high-pass filter.

7. Installation as claimed in claim 6, said high-pass filter comprising a capacitive series element having ohmic series and shunt resistances connected thereto for forming said voltage divider, and said voltage-controlled variable resistance being a field-effect transistor connected in parallel to said shunt resistance.

8. Installation as claimed in claim 7, said field-effect transistor having a control electrode;

a condensor being connected to said electrode so as to form control means for controlling said transistor, said condensor having a discharge arrangement, said condensor being charged to a bias voltage value for maintaining said transistor at a high resistance value, such as a transistor blocking-voltage at signals below the threshold of said threshold discriminator, and being discharged at signals above the threshold by said discharge arrangement at increasing control voltage values of said transistor.

9. Installation as claimed in claim 8, said discharge arrangement comprising a control voltage amplifier having at least one charging transistor, said transistor being controlled into a conductive condition upon the electrical signal exceeding the threshold of said threshold discriminator and the condensor discharges through its collector-emitter section to an extent until the signal again drops below the threshold.

10. Installation as claimed in claim 9, said condensor being discharged at considerably lower time constants than the charging thereof.

11. Installation as claimed in claim 9, said control voltage amplifier comprising an input transistor forming said threshold discriminator in conjunction with an emitter-sided voltage divider for the emitter bias voltage and a base-sided voltage divider having a blocking diode for the electrical signal, and including a switching transistor for switching in of the charging transistor for the condensor upon exceeding a signal threshold value.

12. Installation as claimed in claim 8, comprising an operative point control transistor including a field-effect transistor, said condensor and field-effect transistor in said high-pass filter being actuated by a bias voltage generator for variation of the condensor-bias voltage values for the high transistor resistance.

13. Installation as claimed in claim 12, comprising frequency voltage converter receiving said electrical signal being connected to said operative point control transistor and adapted to detect the incidence frequency of significant amplitude values in the electrical signal and to generate an output voltage in correspondence with said incidence frequency, said control transistor controlling the field-effect transistor in said high-pass filter in dependence upon this output voltage for so long in the direction of lower resistance values until the incidence frequency of the significant amplitude values at the frequency voltage converter drops below a predetermined minimum value.

14. Installation as claimed in claim 13, comprising a second threshold discriminator for detecting the occurrence of the significant signal values at said frequency voltage converter, said threshold discriminator having the threshold thereof adjusted to said significant signal values.

15. Installation as claimed in claim 14, said threshold of said second threshold discriminator being adjusted to a significant value which lies in the range of the expected highest amplitude of continually occurring static voltage, such as power supply hum, which is superimposed on the inherent electrical signal.

16. Installation as claimed in claim 14, said second threshold discriminator comprising a transistor forming a threshold switch, said transistor adapted to be controlled into a conductive condition upon the transistor input voltage exceeding the switching voltage of said transistor inclusive the zener voltage of a zener diode located in the emitter circuit of said transistor.

17. Installation as claimed in claim 16, comprising a voltage multiplier including series capacitances and parallel diodes, said transistor being connected to said voltage multiplier across a collector resistance, said voltage multiplier forming said frequency voltage converter;

and an output resistance having a voltage generated therein by said voltage multiplier increasing with the switching pulse of said second threshold discriminator.

18. Installation as claimed in claim 17, comprising diode switching means including a zener diode with a reverse-poled normal semiconductor diode, said output voltage of said voltage multiplier being connected to the source of said control transistor through said diode switching means, said control transistor controlling the field effect transistor of said high-pass filter to higher resistance values for a period until the output signal of the voltage multiplier exceeds the switching voltage of said diode switching means.

19. Installation as claimed in claim 1, comprising a measuring element connected into the measuring signal channel preceding the high-pass filter for detecting the presence of signal components having considerably increased amplitudes in contrast with normal amplitudes;

and a threshold regulator for raising the threshold of the threshold discriminator associated with the control installation for the control of the field-effect transistor in said high-pass filter for a predetermined time interval to a value higher in comparison with a normal value.

20. Installation as claimed in claim 19, comprising a discriminating and blacking-out arrangement for the detection of and blacking-out of pacemaker impulses superimposed on EKG signals, said discriminating and blacking-out arrangement generating an output signal for said threshold regulator upon each occurrence of a pacemaker signal so as to raise the threshold of said threshold discriminator to twice the normal value for a period of 250 milliseconds.

21. Installation as claimed in claim 20, said threshold regulator comprising a transistor having a charging condensor, said charging condensor being charged through a seminconductor diode to a predetermined value by the output signal of said pacemaker impulse detecting and blacking-out arrangement and being controlled into a conductive condition upon the subsequent discharge of said transistor;

and a voltage divider being actuated in response thereto for raising the threshold of said threshold discriminator.