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US 5,335,020 AGranted
IIR ghost cancelling system with reduction of filter instability
AssigneeRCA Thomson Licensing Corporation
InventorCharles B. Dieterich
Life of this patent
Estimating the term…
Abstract
A ghost cancelling system includes a ghost cancelling IIR filter and channel modelling circuitry for generating tap weighting coefficients for programming the ghost cancelling IIR filter. The channel modelling circuitry includes means for calculating the sum of all of the generated weighting coefficient values. If the sum exceeds a predetermined value indicative of the IIR filter becoming unstable, the weighting coefficients are conditionally scaled in a manner to reduce the sum, thus tending to reduce the possibility of filter instability.
Claims9
Multipath signal canceling apparatus comprising:
- a source of input signal;
- a programmable IIR filter including;
- delay elements for providing a plurality of relatively delayed signals, weighting circuits, having input connections for receiving weighting coefficients, said weighting circuits for weighting respective said delayed signals, combining circuitry coupled to said weighting circuits, for combining weighted signals provided by said weighting circuitry, and signal summing means for combining said input signal and output signal provided by said combining circuitry;
- channel modeling means, responsive to said input signal, for generating said weighting coefficients, said channel modeling means arranged to add the magnitudes of the generated weighting coefficients together to generate a sum of weighting coefficients and to scale said weighting coefficients to produce scaled weighting coefficients if said sum of weighting coefficients exceeds a predetermined value, said scaling of said weighting coefficients arranged to reduce said sum of weighting coefficients;
- and
- means for applying said scaled weighting coefficients to said input connections if said sum of weighting coefficients exceeds said predetermined value and for applying said weighting coefficients to said connections otherwise.
3 more elements
Multipath signal canceling apparatus comprising:
- a source of digital input signal;
- a programmable IIR filter including;
- delay elements for providing a plurality of relatively delayed signals, weighting circuits, having input connections for receiving weighting coefficients, said weighting circuits for weighting respective said delayed signals, combining circuitry coupled to said weighting circuits, for combining weighted signals provided by said weighting circuits, and a digital adder having a limited dynamic range, for combining said digital input signal and output signal provided by said combining circuitry;
- channel modeling means, responsive to said digital input signal, for generating said weighting coefficients;
- a detector coupled to said IIR filter for detecting potential IIR filter instabilities including a signal overflow detector responsive to the polarities of input and output signals applied to and available from said digital adder:
- and
- wherein said channel modeling means includes means arranged to add the magnitudes of the generated weighting coefficients together to generate a sum of weighting coefficients and means to provide scaled said weighting coefficients if said sum of weighting coefficients exceeds a predetermined value and IIR filter instabilities are detected, and wherein a sum of said scaled weighting coefficients is less than said sum of weighting coefficients:
- and
- means for applying said scaled weighting coefficients to said input connections if IIR filter instabilities are detected and for applying said weighting coefficients to said input connections otherwise.
6 more elements
Multipath signal canceling apparatus comprising:
- a source of input video signal;
- a programmable IIR filter including signal summing means, having respective input and output terminals, said summing means for combining said input video signal and a signal representing a combination of delayed and weighted versions of signal available at said output terminal of said summing means, said IIR filter having a plurality of weighting circuits with respective input connections for receiving weighting coefficients and output connections for providing said weighted versions;
- means coupled to said summing means for generating an overflow signal OVF indicating occurrences of the dynamic range of said signal summing means being exceeded;
- channel modeling means, responsive to said input video signal, for generating said weighting coefficients and responsive to said overflow signal OVF, for scaling said weighting coefficients when the dynamic range of the summing means is exceeded;
- and
- means for applying said scaled weighting coefficients to said input connections when said dynamic range is exceeded and applying said weighting coefficients to said input connections otherwise.
3 more elements
Dependencies are inferred from the claim text.