Adaptive dual filter echo cancellation
First Claim
1. A dual filter echo canceller for cancelling echos in a telephony system, said dual filter echo canceller comprising:
- an adaptive filter;
a fixed filter coupled to said adaptive filter; and
a digital signal processor configured to implement the adaptive filter and the fixed filter so as to process during one clock cycle an input signal sample within an adaptive dual filter echo cancellation algorithm including coefficient updating, filtering and coefficient copying between the adaptive filter and fixed filter, said digital signal processor further includes;
a sample memory for storing the input signal sample;
a plurality of multipliers, at least one input of each of said plurality of multipliers coupled to an output of said sample memory;
a plurality of adders, an output of each of said plurality of multipliers coupled to at least one of said plurality of adders; and
a plurality of temporary storage devices, an input and output of each of said plurality of temporary storage devices selectively coupled to at least one of said plurality of multipliers and said plurality of adders.
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Accused Products
Abstract
A digital signal processor that is used for echo cancellation computations is disclosed, which includes parallel multiplier/adders, an input signal sample memory, and a plurality of accumulators for temporarily storing the results of the computations performed. Consequently, not all of the computational results have to be saved in an external data memory, which minimizes data transfer bottlenecks and significantly increases the computational efficiency of the digital signal processor. The adaptive filter coefficient updates can thereby be computed much faster, and the adaptive filter coefficients can be copied much faster from one filter to the other. The computational complexity of the digital signal processor is significantly less than that of prior digital signal processors.
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Citations
18 Claims
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1. A dual filter echo canceller for cancelling echos in a telephony system, said dual filter echo canceller comprising:
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an adaptive filter; a fixed filter coupled to said adaptive filter; and a digital signal processor configured to implement the adaptive filter and the fixed filter so as to process during one clock cycle an input signal sample within an adaptive dual filter echo cancellation algorithm including coefficient updating, filtering and coefficient copying between the adaptive filter and fixed filter, said digital signal processor further includes; a sample memory for storing the input signal sample; a plurality of multipliers, at least one input of each of said plurality of multipliers coupled to an output of said sample memory; a plurality of adders, an output of each of said plurality of multipliers coupled to at least one of said plurality of adders; and a plurality of temporary storage devices, an input and output of each of said plurality of temporary storage devices selectively coupled to at least one of said plurality of multipliers and said plurality of adders. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A method for cancelling echos using an echo canceller including an adaptive filter and a fixed filter each implemented in a digital signal processor capable of processing during one clock cycle an adaptive dual filter echo cancellation algorithm for an input signal sample, said digital signal processor includes:
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a sample memory for storing the input signal sample; a plurality of multipliers, at least one input of each of said plurality of multipliers coupled to an output of said sample memory; a plurality of adders, an output of each of said plurality of multipliers coupled to at least one of said plurality of adders; and a plurality of temporary storage devices, an input and output of each of said plurality of temporary storage devices selectively coupled to at least one of said plurality of multipliers and said plurality of adders, said method comprising the steps of; computing a first output signal from the adaptive filter; responsive to the first output signal, updating a coefficient of the adaptive filter; and copying the updated coefficient of the adaptive filter to the fixed filter;
orcopying a fixed coefficient of the fixed filter to the adaptive filter. - View Dependent Claims (15, 16, 17, 18)
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Specification