Analog Devices,inc.

David Lamb

Yang Pan

Khiem Quang Nguyen

Adam R Spirer

Luiz Chamon

Vitor H Nascimento

In a cascaded integrator comb (CIC) filter, a time-varying gain is added before the last integrating stage transforming its sub optimal boxcar impulse response into an FIR filter of arbitrary length. Make the coefficients sparse and taking them from a set of small integers leads to an efficient hardware implementation that does not compromise any of the essential CIC filter characteristics especially the overflow handling. The proposed sparse CIC structure can improve the worst case stop band attenuation by as much as 10 dB while occupying 77% of the chip area and consuming 30% less power compared to a standard a 5order CIC filter, and reducing the overall bit growth of the filter and the amount of high rate operations. Design examples are given illustrating the advantages and flexibility of the proposed structure.

Sparse cascaded-integrator-comb filters

A discrete-time (e.g., digital) filter can be used as an interpolation filter for processing an oversampled input signal, such as included as a portion of a sigma-delta digital-to-analog conversion circuit. An interpolation filter control circuit can be configured to adjust a filter order of the discrete-time interpolation filter at least in part in response to information indicative of an envelope signal magnitude. For example, higher-level input signals might be processed using an interpolation filter having a stop-band attenuation that is more stringently-specified (e.g., having greater attenuation) than a corresponding attenuation used for lower-level input signals. The filter order can be variable, such as varied in response to a detected envelope magnitude of the input signal to achieve power savings as compared to a filter having fixed parameters.

Envelope-dependent order-varying filter control

An asynchronous sample rate converter prevents the folding back of a signal in the passband of an input sample rate into the passband of the output sample by adaptively controlling the decimation rate. The ASRC includes an adaptive decimation rate controller that selectably controls a decimation filter based on the ratio of the input sampling rate to the output sampling rate. By adaptively controlling the decimation rate in the ASRC, a significant amount of area and power is saved.

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Medford, MA, United States of America

David Lamb