Aligning Moving Average Windows with Converters to Eliminate Aliasing Artifacts
Aligning moving average window lengths to match converter sample periods places exact spectral nulls over periodic interference to eliminate aliasing artifacts.
Cascade Integrator Comb
Filter Architecture
Digital decimation filters reduce the sampling rate of high-speed data streams without introducing complex multiplier hardware. The cascade integrator comb structure accomplishes this by nesting integrator stages and differentiator stages in series. This topology is particularly efficient in delta-sigma converters where high-speed decimation is necessary.
Frequency Response
Gain characteristics of the filter shape the signal passband and determine the attenuation of out-of-band noise. When using a cascade integrator comb, the frequency response exhibits a droop in the passband that requires a subsequent compensating filter. This multi-stage filtering approach ensures that the output signal remains flat across the band of interest.
Register Width
Arithmetic overflow presents a risk in the integrator stages because the gain increases with each added block. System designers prevent this by ensuring that the register width is sufficient to accommodate the maximum possible growth of the digital word. This bit growth is mathematically defined by the number of stages and the decimation ratio, enabling deterministic hardware sizing that avoids any data truncation.
Noise Control
Aliasing of high-frequency noise occurs if the attenuation of the comb filter is insufficient at the folding frequencies. This limitation dictates the minimum number of integrator stages required for a given resolution.