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US 4,223,389 AGranted
Recursive digital filter having means to prevent overflow oscillation
AssigneeHitachi, Ltd.
InventorsEiichi Amada, Makoto Ohnishi
Life of this patent
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Abstract
This invention has been made in order to prevent the malfunction due to an overflow, of a combinatorial type recursive digital filter whose feedback side is of the second or higher order. Means for detecting the overflow of the output of an arithmetic unit which executes an addition within the filter is additionally provided, and when the overflow has developed, the contents of shift registers for delay on, at least, the feedback side are reset by an output from the detecting means.
Claims9
A recursive digital filter comprising:
- (a) first means to which an m-bit digital input signal x(n) is applied,
- (b) calculating means having an input and an output means, said input means connected to said first means, for delivering from said output means thereof a digital signal y(n) shown by a formula, ##EQU9## where n represents a natural number, N and M are orders representing a delay of signal transmission, and a.sub.k and b.sub.k are coefficients with a.sub.M, b.sub.N .noteq.0, and N.gtoreq.2,
- (c) second means including first and second delay means connected in series, said second means being connected between the output means and the input means of said calculating means for delaying an m-bit signal of said digital signal y(n) by two sampling periods or more from said input signal x(n) and for feeding back the delayed signal to the input means of said calculating means,
- (d) overflow detector means connected to the output means of said calculating means and to the first and second delay means of said second means, for supplying a signal for setting the contents of both said first and second delay means into a specified state when the value of said digital signal y(n) exceeds a predetermined value, and
- (e) third means coupled to said first delay means of said second means for delivering an m-bit digital signal y(n) as the output of the filter.
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A recursive digital filter comprising:
- (a) an input terminal into which an m-bit digital input signal x(n) is applied;
- (b) an output terminal for delivering a digital signal y(n);
- (c) calculating means, connected between said input terminal and said output terminal, for converting said input signal x(n) into said signal y(n) which satisfies, ##EQU10## where n represents a natural number, M and N are orders representing a delay of signal transmission, and a.sub.k and b.sub.k are coefficients with a.sub.M, b.sub.N .noteq.0, and N.gtoreq.2, said calculating means including,
- (1) first and second delay means connected in series to each other, each of which has an m-bit data capacity,
- (2) first multiplier means, connected to said second delay means, for multiplying the output signal of said second delay means by a first coefficient b.sub.k,
- (3) first summation means, connected between said input terminal and the output of said first multiplier means, for adding at least said input signal x(n) and the output signal of said first multiplier means and coupled to the first delay means for supplying the output thereof to said first delay means,
- (4) second multiplier means, connected to said first summation means, for multiplying the output signal of said first summation means by a second coefficient a0,
- (5) third multiplier means, connected to said second delay means, for multiplying the output signal of said second delay means by a third coefficient a.sub.k, and
- (6) second summation means, connected between said second and third multiplier means, for adding at least the output signal of said second multiplier means and the output signal of said third multiplier means, and coupled to the output terminal for supplying the output of the second summation means to said output terminal;
- and
- (d) an overflow detector, connected to said first summation means and said first and second delay means for supplying a signal for setting the contents of said first and second delay means into a specified state when the value of the output signal of said first summation means exceeds a predetermined value.
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Dependencies are inferred from the claim text.