US 4,545,027 AGranted

Digital adaptive correlating filter

AssigneeUnited Technologies Corporation

InventorsThomas Posluszny, Oscar Oliver, Sr.

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Abstract

An adaptive digital filter employs sequentially connected shift register stages to produce an N-fold correlation of pulses within a pulse train that satisfy search criteria. Once a signal has been acquired, a processor adaptively changes the tolerance length of the shift registers; the shifting clock and the number of stages to generate a real-time processed signal that tracks the source of the pulse train.

Claims4

Dependent claims

An adaptive digital correlating filter system for analyzing a train of pulses comprising:

at least two stages of sequentially connected clock-controlled correlation devices for producing a stage output signal in response to the occurrence within said pulse train of a pair of pulses within a first tolerance range, in which
a first stage correlation device comprises a first fixed-length shift register connected to a first multi-cell shift register, each cell of which multi-cell shift register produces a cell signal for correlation and an output signal to the next cell in said multi-cell shift register and means for generating a first stage output signal for signalling a coincidence between an N'th pulse at an end of said fixed-length shift register and a pulse in one of said cells of said multi-cell shift register;
and
a second stage correlation device is connected to at least one output of said first stage correlation device, which second stage correlation device comprises a second multi-cell shift register connected to a second fixed-length shift register, the order of connection being opposite for said first stage and second stage correlation devices;
and
means for generating a second stage output signal for signalling a two-fold correlation in said first and second stages;
characterized in that:
said first and second correlation devices include first and second means for length control connected to said first and second multi-cell shift registers for rendering inactive sequentially the cell signals of those cells furthest from said first and second fixed-length shift registers, whereby the effective length of said first and second stage correlation devices may be controlled;
said clock has a variable clock repetition rate set initially to a value corresponding to an expected signal in said train of pulses;
and
said filter system further includes processing means connected to said at least two stages of correlation devices and to said clock, which processing means adaptively controls said effective lengths of said at least two stages of correlation devices and said variable clock repetition rate to adjust a tolerance parameter of said correlation devices from a predetermined loose tolerance for signal acquisition to a second, tighter, operating tolerance for efficient signal discrimination.

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Dependencies are inferred from the claim text.

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Abstract

An adaptive digital correlating filter system for analyzing a train of pulses comprising:

at least two stages of sequentially connected clock-controlled correlation devices for producing a stage output signal in response to the occurrence within said pulse train of a pair of pulses within a first tolerance range, in which
a first stage correlation device comprises a first fixed-length shift register connected to a first multi-cell shift register, each cell of which multi-cell shift register produces a cell signal for correlation and an output signal to the next cell in said multi-cell shift register and means for generating a first stage output signal for signalling a coincidence between an N'th pulse at an end of said fixed-length shift register and a pulse in one of said cells of said multi-cell shift register;
and
a second stage correlation device is connected to at least one output of said first stage correlation device, which second stage correlation device comprises a second multi-cell shift register connected to a second fixed-length shift register, the order of connection being opposite for said first stage and second stage correlation devices;
and
means for generating a second stage output signal for signalling a two-fold correlation in said first and second stages;
characterized in that:
said first and second correlation devices include first and second means for length control connected to said first and second multi-cell shift registers for rendering inactive sequentially the cell signals of those cells furthest from said first and second fixed-length shift registers, whereby the effective length of said first and second stage correlation devices may be controlled;
said clock has a variable clock repetition rate set initially to a value corresponding to an expected signal in said train of pulses;
and
said filter system further includes processing means connected to said at least two stages of correlation devices and to said clock, which processing means adaptively controls said effective lengths of said at least two stages of correlation devices and said variable clock repetition rate to adjust a tolerance parameter of said correlation devices from a predetermined loose tolerance for signal acquisition to a second, tighter, operating tolerance for efficient signal discrimination.

8 more elements