Wave transmission lines and networks – Coupling networks – Time domain filters
Patent
1979-06-21
1981-01-06
Lieberman, Eli
Wave transmission lines and networks
Coupling networks
Time domain filters
333 18, H03A 1500, H03A 1700
Patent
active
042439590
ABSTRACT:
Adaptive filters are commonly used in echo cancelers and automatic equalizers. Usually adaptive filters include a tapped delay line and apparatus coupled to the delay line for producing a tap coefficient signal, whose sign and magnitude indicate the appropriate correction in adjusting the filter. However, in the presence of input signals having a partial frequency band spectrum, known filters tend to become unstable, e.g., tap coefficient signals blow up. The instant arrangement includes apparatus for weakly driving the tap coefficient signals to optimal values. As illustrated in a deceptively simple embodiment, a tap coefficient updating component is extended through a one's complement converter to a first input of a binary adder. A two's complement output of the adder is fed back to a second input of the adder. The sign of the adder output is also provided to a CARRY-IN input terminal of the adder. Functionally, a unit leak is introduced in the least significant bit of the adder output tap coefficient signal whenever the updating component and the tap coefficient signal are of opposite algebraic signs. Otherwise, no leak is introduced. Thereby the tap coefficient signal is weakly driven toward zero.
REFERENCES:
patent: 3499999 (1970-03-01), Sondhi
patent: 3500000 (1970-03-01), Kelly et al.
patent: 4129753 (1978-12-01), Duttweiler
Peatman, The Design of Digital Systems, McGraw-Hill Book Co., (1972), pp. 23-26.
Helder et al., Improving Transmission on Domestic Satellite Circuits, Bell Lab. Record, Sep. 1977, pp. 202-207.
Duttweiler, IEEE Transactions on Communications, vol. COM-26, No. 5, May 1978, pp. 647-653.
Bell Telephone Laboratories Incorporated
Lieberman Eli
Roddy Richard J.
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