Broadcom Corporation

Robert A Hawley

Steven T Jaffe

Loke Kun Tan

Tian-Min Liu

Robindra B Joshi

Huan-Chang Liu

An electronic, programmable filter is disclosed which selectively removes interference, noise or distortion components from a frequency band without perturbing any of the other signals of the band. An input frequency band such as a television channel spectrum is initially demodulated to baseband and applied to the input of the filter. The baseband spectrum is combined in a complex mixer with a synthesized frequency signal that shifts the spectrum a characteristic amount, in the frequency domain, so as to position an interference component in the region about DC. Once shifted, the frequency components about DC are removed by DC canceler circuit and the resulting spectrum is mixed with a subsequent synthesized frequency signal which shifts the spectrum back to its original representation and baseband. The frequency signals are developed by a programmable frequency synthesizer which a user may program with an intelligence signal that defines the frequency location of an interference signal within the spectrum. Filter blocks may be added or subtracted in order to optimize the filter response for any number of interference components for which rejection is desired.

NTSC interference rejection filter

Clock signals and digital data signals at a variable frequency are introduced to the input of a FIFO and are passed from the FIFO at a second (or intermediate) frequency controlled by a numerically controlled oscillator. To regulate the frequency of the signals from the numerically controlled oscillator, the phases of the clock signals at the variable frequency are compared in a phase detector with the phases of the signals from the numerically controlled oscillator to generate an error signal. The error signals and the signals at a fixed sampling frequency higher than the intermediate frequency regulate the frequency of the signals from the numerically controlled oscillator and thus the frequency of the digital data signals from the FIFO. The digital data signals from the FIFO are converted to a pair of signals at the second frequency. The pair of signals at the second frequency have individual ones of a plurality of analog levels dependent upon a code indicated by successive pairs of the digital data signals. The signals at the second (or intermediate) frequency modulate a pair of trigonometrically related signals at the fixed sampling frequency. The modulated signals at the fixed sampling frequency are combined and the combined signals are sampled at the fixed sampling frequency to corresponding analog values by a digital-to-analog converter.

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Tustin, CA, United States of America

Robert A Hawley