Compact-structure input-weighted multitap digital filters
AssigneeRCA Corporation
InventorJames H. Arbeiter
Life of this patent
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Abstract
The number of bits per digital sample that is required to be stored in each of one or more delay means of an input-weighted multitap digital filter is reduced with respect to that required by the prior art. The savings in storage hardware becomes more and more significant as the number of samples stored in each delay means becomes larger and larger. A plurality of filter delay means, each storing as many as 800 samples, are used in vertical filters of image processors operating in real time on horizontally scanned two-dimensional images, such as television images.
Claims11
In an m-tap input-weighted digital filter (where m is a first integer of three or more) responsive to an input stream of successive digital samples for deriving a filtered output stream of successive digital samples;
- wherein;
- (a) each of said input and output digital samples is defined by Q-bits (where Q is a second given integer of three or more);
- (b) each of said input digital samples is applied to a first of the m taps of said filter, and the relative weight of the first of the m taps of said filter is no greater than one-fourth, thereby deriving a stream of weighted input digital samples for the first of the m taps;
- (c) at least each of a subset of the m taps that include the first of the m taps has individually associated therewith a delay means for storing each of S successive digital samples for a given time interval (where S is a third given integer), the delay means individually associated with the first of the m taps having each of said stream of weighted input digital samples applied as an input thereto;
- and
- (d) at least the delay means individually associated with the first of the m taps for storing digital samples defined by no more than Q'-bits (where Q' is any integer having a value that is smaller than that of the second given integer Q and yet is large enough to store all the significant bits of each weighted input digital sample);
- the improvement wherein said filter is comprised of:
- a first component polyphase input-weighted filter responsive to at least a first portion of said input stream, said first component filter having respective taps which comprises solely all the odd ones of said m-taps of said filter, the sum of the weights of all said odd ones of said m-taps having a value substantially equal to one-half and an individual one of said S-sample delay means associated with at least each but the last of said odd ones of said m-taps;
- a second component polyphase input-weighted filter responsive to at least a second portion of said input stream, said second component filter having respective taps which comprises solely all the even ones of said m-taps of said filter, the sum of the weights of all said even ones of said m-taps having a value substantially equal to one-half an individual one of said S-sample delay means associated with at least each but the last of said even ones of said m-taps, and at least the delay means individually associated with the first of said even ones of said m-taps for storing digital samples defined by no more than Q'-bits;
- and
- combining means coupled to both the last of said odd ones of said m-taps of said first component polyphase filter and the last of said even ones of said m-taps of said second component polyphase filter for deriving said filtered output stream of successive digital samples of said input-weighted digital filter.
Dependencies are inferred from the claim text.