Anti-aliasing filter circuit for oscilloscopes
First Claim
1. An anti-aliasing filter circuit for a digital oscilloscope having a controllable sweep-rate and including digitizing means for converting an analog signal to digital values for storage in said digital oscilloscope, said circuit comprising:
- means for providing a signal input,a plurality of low pass analog filters for receiving said signal input,a digital filter for receiving said signal input, said digital filter having an electrically controllable pass band,and means for controlling the sweep-rate of said oscilloscope simultaneously with selection of signal outputs of said analog filters at higher sweep-rates and selection of the signal output of said digital filter at slower sweep-rates for coupling to said digitizing means while controlling the pass band of said digital filter at slower sweep rates in order to pass selected frequencies less than half the sampling rate of said digitizing means.
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Abstract
A digital storage oscilloscope is provided with an anti-aliasing filter circuit utilizing a first plurality of switchable analog filters that bandwidth limit frequencies greater than half the oscilloscope'"'"'s sampling frequency, and a digital transversal filter effective at lower sweep rates and sampling rates for also bandwidth limiting frequencies greater than half the sampling frequency. The digital transversal filter is controllable to provide a different band pass characteristic for different sweep and sample rates. Both the selection of filters and the control of the digital filter are responsive to the oscilloscope'"'"'s selection of sweep rate.
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Citations
11 Claims
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1. An anti-aliasing filter circuit for a digital oscilloscope having a controllable sweep-rate and including digitizing means for converting an analog signal to digital values for storage in said digital oscilloscope, said circuit comprising:
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means for providing a signal input, a plurality of low pass analog filters for receiving said signal input, a digital filter for receiving said signal input, said digital filter having an electrically controllable pass band, and means for controlling the sweep-rate of said oscilloscope simultaneously with selection of signal outputs of said analog filters at higher sweep-rates and selection of the signal output of said digital filter at slower sweep-rates for coupling to said digitizing means while controlling the pass band of said digital filter at slower sweep rates in order to pass selected frequencies less than half the sampling rate of said digitizing means. - View Dependent Claims (2, 3)
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4. An anti-aliasing filter circuit for a digital oscilloscope having a sweep-rate control and including digitizing means for converting an analog signal to digital values for storage in said digital oscilloscope, said circuit comprising:
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a signal input terminal, a plurality of low pass filters having different bandwidths and means for coupling the input of each of said filters to said signal input terminal, and means for selecting the ouput of one of said filters and for coupling the selected output to said digitizing means in accordance with the sweep rate control of said oscilloscope so that the pass band is reduced at lower sweep and sampling rates to selected frequencies less than half the sampling rate of said digitizing means.
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5. An anti-aliasing filter circuit for a digital oscilloscope having a sweep-rate control and including digitizing means for converting an analog signal to digital values for storage in said digital oscilloscope, said circuit comprising:
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a digital transversal filter including a tapped analog delay device providing an output summed at the taps thereof, and means for coupling said digital transversal filter to receive a signal input, wherein parameters of said digital transversal filter are selected in response to the setting of the sweep rate control of said oscilloscope to provide a reduced low pass characteristic substantially in proportion to lowering of the sweeep rate in order to pass selected frequencies less than half the sampling rate of said digitizing means. - View Dependent Claims (6, 7)
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8. An anti-aliasing filter circuit for a digital oscilloscope having a sweep-rate control and including digitizing means for converting an analog signal to digital values for storage in said digital oscilloscope, said circuit comprising:
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a signal input terminal, a plurality of low pass analog filters having different bandwidths and means for coupling the input of each of said analog filters to said signal input terminal, a low pass digital transversal filter and means for coupling the input of said digital transversal filter to said signal input terminal, and means for selecting between the ouput of one of said analog filters and the output of said digital transversal filter and for coupling the selected output to said digitizing means in accordance with the setting of the sweep rate control of said oscilloscope including providing the output of one of said analog filters as a digitizing input at faster sweep rates wherein the selected output is sampled at a higher sampling rate, and providing the output of said digital transversal filter as a digitizing input at slower sweep rates wherein the selected output is sampled at a lower sampling rate, said digital transversal filter being responsive to a particular selected slower sweep rate for setting the parameters of said digital transversal filter to provide a diminshed pass band as said sweep rate and sampling rate are reduced in order to prevent aliasing in the presentation of an input signal waveform by said oscilloscope. - View Dependent Claims (9, 10, 11)
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Specification