Patent review

PATENT REVIEW

PATENT: United States Patent, SIGNAL PROCESSING SYSTEM AND METHOD FOR
               ENHANCED CASCADED INTEGRATOR-COMB INTERPOLATION FILTER
               STABILIZATION

PATENT NUMBER: US5880973

In this patent, overflow detection circuit monitors the output of the CIC (Cascaded Integrated Comb)interpolation filter for an overflow condition which is indicative of filter instability. When an Overflow Condition is detected, the reset circuitry automatically resets the filter, thereby eliminating the instability. CIC interpolation filters are constructed as a series of ‘N’comb filter circuits (subtractors), followed by a Zero pad circuit, followed by a series of “N” integrator circuits(adders). The comb section of the filter operates at a low sample rate, Whereas the integrator section of the filter operates at a high sampling rate. Typically, the interpolation factor (R) is set between 2 and 10,000. The number of stages of filter increases accuracy. Implementing a CIC interpolation filter generally involves the three requirements that the filter must be reset before use, addition and subtractions must be performed using modulo arithmetic and the Word size in the subtracters, adders, and storage elements must be large enough to accommodate the arithmetic gain of the filter. This circuit checks whether overflow is there or not,if no then it will proceed further and if yes then it will reset filter. This invention detects instabilities in the CIC interpolation filter by continuously monitoring the output samples of the filter.

PATENT LINK: https://www.google.ch/patents/US5880973