Review on Patent

Signal processing system and method for enhanced cascaded integrator-comb interpolation filter stabilization 
Patent No. US 5880973 A
A signal processing system and method for stabilizing cascaded integrator-comb (CIC) interpolation filters. The signal processing system includes an overflow detection circuit and reset circuitry. The overflow detection circuit monitors the output of the CIC 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. ransmission filter 102 first interpolates the input samples (31.5 MHz samples on bus 112) by a factor of 4, as well as shapes the spectral response. In general, implementation of transmission filter 102 is well known in the art. For example, a conventional finite impulse response (FIR) filter, with one or two stages, can be used. With respect to a QPSK-based cellular system, transmission filter 102 can be implemented as a conventional root-raised cosine (RRC) pulse shaping filter. In this embodiment, however, transmission filter 102 is a low-pass filter with a 30 KHz cut-off frequency. 

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