Interference filter
First Claim
1. An interference filter for the removal of AC interference caused by power lines from a signal containing information to be processed comprising means for filtering said interference from said signal and producing a filtered signal free of interference, means for combining the filtered signal with the unfiltered signal to produce an interference signal, means for reversing the phase of the interference signal relative to the interference in the first said signal and means for combining the last said interference signal with the first said signal to produce a resultant signal wherein the interference is cancelled.
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Accused Products
Abstract
An interference filter for the removal of power line interference from amplifying systems, such as electrocardiographs, which includes a band-rejection filter tuned to reject the power line frequency interference, a differential amplifier to which the signal being amplified and the output of the notch filter are applied to produce an output consisting of only the interference signal. The interference signal is fed to and stored in a memory which is constantly updated and the output of the memory is then summed with the original signal. Since the phase of the output of the memory is reversed from the interference in the original signal, only the original signal will result. An electronic switch is connected between the output of the differential amplifier and the memory and is operated by a velocity detector connected with the output of the band-rejection filter. If at any time the velocity detector senses a rate of rise of the incoming signal exceeding a selected value, it functions to open the switch for a predetermined period and thereafter closes the switch. This procedure in the case of electrocardiographs, prevents distortion of electrocardiographic signals.
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Citations
13 Claims
- 1. An interference filter for the removal of AC interference caused by power lines from a signal containing information to be processed comprising means for filtering said interference from said signal and producing a filtered signal free of interference, means for combining the filtered signal with the unfiltered signal to produce an interference signal, means for reversing the phase of the interference signal relative to the interference in the first said signal and means for combining the last said interference signal with the first said signal to produce a resultant signal wherein the interference is cancelled.
- 7. An interference filter for the removal of power line interference in an electrocardiograph amplifying system comprising a band rejection filter for rejecting a frequency band which includes said interference, said filter having an input and output, a differential amplifier having two inputs and an output, means for feeding a signal including said power line interference to the input of said filter and to one input of said amplifier, means for feeding the output of said filter to the other input of said amplifier, said amplifier cancelling the electrocardiographic signal and producing an output containing only said interference, a memory having an input and output, means for feeding said interference to the input of said memory and constantly updating the memory, a summing junction, and means for feeding the contents of said memory and said signal containing said interference to said summing junction thereby cancelling the interference from said signal without material distortion of said signal.
Specification