Method and apparatus for analog D.C. offset cancellation

Details Method and apparatus for analog D.C. offset cancellation Method and apparatus for analog D.C. offset cancellation

1990-04-10

1992-08-25

Chin, Stephen

Pulse or digital communications

Repeaters

Testing

36472419, H03H 730

Patent

active

051425521

ABSTRACT:
The present invention utilizes a decision feedback equalizer (DFE)/finite impulse response filter. A plurality of taps of the equalizer supply coefficients to the input function and are updated in a feedback loop. An additional DC tap is provided, with a constant value as its input source. Within reasonable limits, the constant term (i.e. D.C.) in an analog input signal is subtracted out by the action of the constant value DC tap. The coefficients are updated by a decision feedback means such that phase, amplitude and DC offset may all be corrected. In the preferred embodiment, the filter is a T/2 spaced filter in which two samples per baud are utilized by the filter. The filter outputs a complex word which is coupled to a quantizer. The actual constellation locations are compared to the ideal locations in a difference block so that offset errors may be detected. The difference signal is used to update the coefficient values. One of the coefficients so generated is the DC tap in the filter. The product of the modified tap value and the constant input term is combined with the convolutional sum of the input signal to remove constant terms resulting from DC offset in the input signal.

REFERENCES:
patent: 3943448 (1976-03-01), Motley et al.
patent: 4021738 (1977-05-01), Gitlin et al.
patent: 4384355 (1983-05-01), Werner
patent: 4571732 (1986-02-01), Piriani et al.
patent: 4646325 (1987-02-01), Zuranski et al.

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