Communication system including a digital roll-off filter

Details Communication system including a digital roll-off filter Communication system including a digital roll-off filter

1995-12-15

1997-07-15

Chin, Wellington

Pulse or digital communications

Equalizers

Automatic

375229, 375234, 375235, 3647242, 381103, H03H 730, H03H 740

Patent

active

056489889

ABSTRACT:
A transversal type digital roll-off filter receiving a signal n-time sampled from analog signal carrying a pulse train of symbol rate T, includes a transversal type delay line including a plurality of delay elements each having a delay time T
. Nodes are positioned between adjacent two delay elements. The filter further includes a memory for providing first tap rating ratios to control signals of the nodes and a calculation circuit for monitoring pulse forms of the output signal of the filter, and calculating second ratios to additionally control a central node and every n-th node counted from the central node, where the second ratios are calculated to make the output pulse good in shape. The filter acts as a roll-off filter and as an automatic equalizer. In a method of diagnosing the circuits in the above system, a memory in a transmitter further has second tap rating ratios used to diagnose the system, where the first and second ratios are switchably output to a digital filter in the transmitter. The second tap rating ratios allow the first filter itself alone to output good-shape pulses. The method includes the steps of switching the first memory to output the second ratios and comparing an eye diagram with a reference level, at a point after the first filter, to determine a cause of deteriorating the pulse forms.

REFERENCES:
patent: 3560855 (1971-02-01), Schroeder
patent: 3617948 (1971-11-01), Lucky
patent: 3633107 (1972-01-01), Brady
patent: 3978407 (1976-08-01), Forneg, Jr. et al.
patent: 4097807 (1978-06-01), Fujimura
patent: 5050186 (1991-09-01), Gurcon et al.
patent: 5175747 (1992-12-01), Murakami
patent: 5321723 (1994-06-01), Mizoguchi
patent: 5327459 (1994-07-01), Hara et al.
IEEE Journal of Solid-State Circuits, vol. 23, No. 5, Meier et al. "A2 m CMOS Digital Adaptive Equalizer Chip for QAM Digital Radio Modems" Oct. 1988.

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