Signal processor for digital echo canceller
First Claim
1. A system for multiplying first and second multibit factors quantized in conformity with a pseudo-logarithmic compression characteristic, wherein each factor has an exponent and a mantissa, comprising first circuit means for receiving the mantissas and for generating a data signal having a value in accordance with the sum and the product of the mantissas, said first circuit means also generating exponent carry signals as required by the values of the mantissas;
- second circuit means for receiving the exponents and said carry signals and for generating a control signal having a value in accordance with the sum thereof; and
shifter circuit means for receiving said data and said control signals, said shifter circuit means having a plurality of outputs greater in number than the number of bits in said data signal and generating said data signal at individual ones of said outputs in accordance with the value of said control signal.
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Accused Products
Abstract
A processor for an echo canceller generates an estimate of an actual echo on an echo path and applies the same to a subtractor circuit in the path to cancel the echo. To generate the echo estimate, the processor multiplies A-law digitally encoded samples of signals which cause the echo by A-law digitally encoded samples of impulse responses of the echo path and sums a plurality of the products. The particular manner of multiplying the A-law samples produces a product which is a precise linear representation of the product of the linear equivalents of the samples, and no errors or approximations occur in the multiplication or in generation of the echo estimate.
15 Citations
37 Claims
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1. A system for multiplying first and second multibit factors quantized in conformity with a pseudo-logarithmic compression characteristic, wherein each factor has an exponent and a mantissa, comprising first circuit means for receiving the mantissas and for generating a data signal having a value in accordance with the sum and the product of the mantissas, said first circuit means also generating exponent carry signals as required by the values of the mantissas;
- second circuit means for receiving the exponents and said carry signals and for generating a control signal having a value in accordance with the sum thereof; and
shifter circuit means for receiving said data and said control signals, said shifter circuit means having a plurality of outputs greater in number than the number of bits in said data signal and generating said data signal at individual ones of said outputs in accordance with the value of said control signal. - View Dependent Claims (2, 3, 4)
- second circuit means for receiving the exponents and said carry signals and for generating a control signal having a value in accordance with the sum thereof; and
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5. A system for multiplying first and second A-law encoded binary factors, the first factor having an exponent xe, a mantissa xm and a sign bit and the second factor having an exponent he, a mantissa hm and a sign bit, comprising first circuit means for receiving the mantissas at inputs thereto and for generating at outputs therefrom the quantities (xm +1) and (hm +1) and active carry bits xc and hc whenever the respective quantity equals zero, which occurs whenever the respective mantissa equals the maximum step value for the range of A-law encoding used;
- multiplier circuit means for receiving said quantities and for multiplying the same to generate a product signal Pm ;
second circuit means for receiving said quantities and controllable to generate an output signal Sm which equals either zero, one of said quantities or a summation of both of said quantities;
a first adder circuit for generating at an output therefrom a summation Σ
m of signals at inputs thereto, said first adder circuit receiving at its inputs said signals P.sub. m and Sm, and one of said adder circuit and said second circuit means providing 24 weighting for said signal Sm in said summation signal Σ
m ;
a second adder circuit for generating at an output therefrom a summation signal Σ
e of signals at inputs thereto, said second adder circuit receiving at its inputs the exponents xe and he ;
a decoder circuit for receiving the exponents xe and he and said carry signals xc and hc, said decoder circuit having outputs which are selectively rendered active in accordance with the values of xe, he, xc and hc, wherein two of said outputs Ec1 and Ec2 are applied to inputs to said second adder circuit, another two of said outputs xi and hi are applied to said second circuit means to control the same, and one output 28 is applied to one of said second circuit means and said first adder circuit to cause the introduction, when said output is active, of 28 into said signal Σ
m ; and
shifter circuit means having data inputs for receiving said first adder circuit output signal Σ
m and shift control inputs for receiving said second adder circuit output signal Σ
e, said shifter circuit having a plurality of outputs greater in number than the number of bits in said signal Σ
m and generating said signal Σ
m at selected ones of said outputs in accordance with the value of said signal Σ
e. - View Dependent Claims (6, 7, 8, 9, 10, 11, 12)
- multiplier circuit means for receiving said quantities and for multiplying the same to generate a product signal Pm ;
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13. A system for multiplying first and second A-law encoded binary factors wherein the first factor has a non-zero exponent xe, a mantissa xm and a sign bit and the second factor has a non-zero exponent he, a mantissa hm and a sign bit, comprising first circuit means for receiving the mantissas at inputs thereto and for generating at outputs therefrom the quantities (xm +1) and (hm +1) and active carry bits xc and hc whenever the respective quantity equals zero, which occurs whenever the respective mantissa equals the maximum step value for the range of A-law encoding used;
- multiplier circuit means for receiving said quantities and for multiplying the same to generate a product signal Pm ;
a first binary adder circuit for receiving said quantities and for generating a summation signal Sm of the same;
a second binary adder circuit for generating at an output therefrom a summation signal Σ
m of signals at inputs thereto, said second binary adder receiving said signals Pm and Sm at inputs thereto and one of said first and second binary adder circuits providing 24 weighting for said signal Sm in said signal Σ
m ;
means for applying a 28 input signal to an input to one of said first and second binary adder circuits so that said signal Σ
m equals (Pm +24 Sm +28);
a third binary adder circuit for receiving at inputs thereto the exponents xe and he and signals representative of said carry bits xc and hc and for generating at an output therefrom a summation signal Σ
e which equals the sum of the exponents plus one (+1) for each active carry bit; and
shifter circuit means having data inputs for receiving said signal Σ
m and shift control inputs for receiving said signal Σ
e, said shifter circuit having a plurality of outputs greater in number than the number of bits in said signal Σ
m and generating said signal Σ
m at selected ones of its outputs in accordance with the value of said signal Σ
e. - View Dependent Claims (14)
- multiplier circuit means for receiving said quantities and for multiplying the same to generate a product signal Pm ;
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15. A system for multiplying first and second A-law encoded binary factors wherein the first factor has an exponent xe equal to zero, a mantissa xm having a value less than the maximum step value for the range of A-law encoding used and a sign bit, and the second factor has a non-zero exponent he, a mantissa hm and a sign bit, comprising first circuit means for receiving the mantissa at inputs thereto and for generating at outputs therefrom the quantities (xm +1) and (hm +1) and an active carry bit hc whenever the quantity (hm +1) equals zero, which occurs whenever the mantissa hm has the maximum step value;
- multiplier circuit means for receiving said quantities and for multiplying the same to generate a product signal Pm ;
a first binary adder circuit for receiving at inputs thereto said quantity (xm +1) and said signal Pm, said binary adder circuit providing 24 weighting for said quantity (xm +1) and generating at an output therefrom a summation signal Σ
m equal to [Pm +24 (xm +1)];
second circuit means for receiving the exponent he and said carry bit hc at inputs thereto and for generating an output signal Σ
e equal to (he +1) if the carry bit hc is inactive or (he +2) if the carry bit hc is active; and
shifter circuit means having data inputs for receiving said signal Σ
m and shift control inputs for receiving said signal Σ
e, said shifter circuit having a plurality of outputs greater in number than the number of bits in said signal Σ
m and generating said signal Σ
m at selected ones of its outputs in accordance with the value of said signal Σ
e. - View Dependent Claims (16)
- multiplier circuit means for receiving said quantities and for multiplying the same to generate a product signal Pm ;
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17. A system for multiplying first and second A-law encoded binary factors wherein the factors have exponents equal to zero, respective mantissas xm and hm each having a value less than the maximum step value for the range of A-law encoding used and sign bits, comprising first circuit means for receiving the mantissas xm and hm, for generating the quantities (xm +1) and (hm +1), and for multiplying said quantities to generate a product signal Pm ;
- shifter circuit means having data inputs for receiving said signal Pm and a shift control input, said shifter circuit having a plurality of outputs greater in number than the number of bits in said signal Pm and generating said signal Pm at selected ones of its outputs as determined by the value of the signal at its shift control input; and
means for applying a signal to said shift control inputs to operate said shifter circuit to shift said signal Pm two places along its outputs. - View Dependent Claims (18)
- shifter circuit means having data inputs for receiving said signal Pm and a shift control input, said shifter circuit having a plurality of outputs greater in number than the number of bits in said signal Pm and generating said signal Pm at selected ones of its outputs as determined by the value of the signal at its shift control input; and
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19. A method of multiplying first and second multibit factors quantized in conformity with a pseudologarithmic compression characteristic, wherein one factor represents a signal that causes an echo on an echo path of a transmission system and the other the impulse response of the system, in order to generate an echo estimate for subtraction from the echo on the echo path, and wherein each factor has an exponent and a mantissa, comprising the steps of summing signals representative of the sum and of the product of the mantissas to generate a data signal;
- generating exponent carry signals as required by the values of the mantissas;
summing the exponents and said carry signals to generate a control signal; and
shifting said data signal by a number of bit places equal to the value of said control signal to generate the product of the factor. - View Dependent Claims (20, 21, 22)
- generating exponent carry signals as required by the values of the mantissas;
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23. A method of multiplying first and second A-law encoded binary factors, wherein one factor represents a signal that causes an echo on an echo path for a transmission system and the other the impulse response of the system, in order to generate an echo estimate for subtraction from the echo on the echo path, and wherein the first factor has a non-zero exponent xe, a mantissa xm and a sign bit and the second factor a non-zero exponent he, a mantissa hm and a sign bit, comprising the steps of incrementing each of the mantissas to generate the quantities (xm +1) and (hm +1);
- generating a carry bit xc and hc whenever a respective quantity (xm +1) and (hm +1) equals zero, which occurs whenever the respective mantissa equals the maximum step value for the range of A-law encoding used;
multiplying said quantities to generate a product Pm thereof;
adding said quantities to generate a summation Sm of the same;
weighting said summation Sm by 24 to generate 24 Sm ;
adding said weighted summation 24 Sm and said product Pm to generate a summation Σ
m thereof;
incrementing said summation Σ
m by 28 so that the same equals (Pm +24 Sm +28);
adding the exponents and incrementing the same by plus one (+1) for each generated carry bit xc and hc to generate a summation Σ
e ; and
shifting said summation Σ
m by a number of bit places equal to the value of said summation Σ
e to generate the product of the factors. - View Dependent Claims (24, 25)
- generating a carry bit xc and hc whenever a respective quantity (xm +1) and (hm +1) equals zero, which occurs whenever the respective mantissa equals the maximum step value for the range of A-law encoding used;
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26. A method of multiplying first and second A-law encoded binary factors, wherein one factor represents a signal that causes an echo on an echo path of a transmission system and the other the impulse response of the system, in order to generate an echo estimate for subtraction from the echo on the echo path, and wherein the first factor has an exponent xe which equals zero, a mantissa xm having a value less than the maximum step value for the range of A-law encoding used and a sign bit, and the second factor has a non-zero exponent he, a mantissa hm and a sign bit, comprising the steps of incrementing each of the mantissas to generate the quantities (xm +1) and (hm +1);
- generating a carry bit hc whenever the mantissa hm has the maximum step value;
multiplying said quantities to generate a product Pm thereof;
weighting said quantity (xm +1) by 24 to generate 24 (xm +1);
adding said weighted quantity 24 (x.sub. m +1) and said product Pm to generate a summation Σ
m thereof;
generating an output signal Σ
e which equals (he +1) if said carry bit hc is inactive or (he +2) if said carry bit hc is active; and
shifting said summation Σ
m by a number of bit places equal to the value of said summation Σ
e to generate the product of the factors. - View Dependent Claims (27, 28)
- generating a carry bit hc whenever the mantissa hm has the maximum step value;
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29. A method of multiplying first and second A-law encoded binary factors, wherein one factor represents a signal that causes an echo on an echo path of a transmission system and the other the impulse response of the system, in order to generate an echo estimate for subtraction from the echo on the echo path, and wherein the factors have exponents equal to zero, respective mantissas xm and hm each having a value less than the maximum step value for the range of A-law encoding used and sign bits, comprising the steps of incrementing each of the mantissas to generate the quantities (xm +1) and (hm +1);
- multiplying said quantities to generate a product Pm thereof; and
shifting said product Pm by two bit places to generate the product of the factors. - View Dependent Claims (30, 31)
- multiplying said quantities to generate a product Pm thereof; and
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32. A system for multiplying first and second multibit factors quantized in confirmity with a pseudologarithmic compression characteristic, wherein each factor has an exponent and a mantissa, comprising first circuit means for receiving the mantissas and for generating a data signal having a value in accordance with a summation of (a) the sum of the mantissas and (b) the product of the mantissas, said first circuit means also generating exponent carry signals as required by the values of the mantissas;
- second circuit means for receiving the exponents and the carry signals and for generating a control signal having a value in accordance with the sum thereof; and
shifter circuit means for receiving said data and said control signals, said shifter circuit means having a plurality of outputs greater in number than the number of bits in said data signal and generating said data signal at individual ones of said outputs in accordance with the value of said control signal. - View Dependent Claims (33, 34)
- second circuit means for receiving the exponents and the carry signals and for generating a control signal having a value in accordance with the sum thereof; and
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35. A method of multiplying first and second multibit factors quantized in conformity with a pseudo-logarithmic compression characteristic, wherein one factor represents a signal that causes an echo on a echo path of a transmission system and the other the impulse response of the system, to generate an echo estimate for subtraction from the echo on the echo path, and wherein each factor has an exponent and a mantissa, comprising the steps of summing signals respresentative of (a) the sum of the mantissas and (b) the product of the mantissas to generate a data signal, generating exponent carry signals as required by the values of the mantissas;
- summing the exponents and said carry signals to generate a control signal; and
shifting said data signal by a number of bit places equal to the value of said control signal to generate the product of the factors. - View Dependent Claims (36, 37)
- summing the exponents and said carry signals to generate a control signal; and
Specification