Multirate Structure
Digital filter architectures perform sample rate alteration without requiring explicit multiplier hardware structures. A cascaded integrator comb filter uses alternating integrator and differentiator stages separated by a rate conversion sampler to perform decimation or interpolation. Processing relies entirely on addition and subtraction operations, making the design efficient for high-throughput hardware implementations.
Sourcing assessment evaluates register bit-growth requirements across filter stages to prevent arithmetic overflow during decimation.
Aliasing Rejection
Integrator stages accumulate continuous input samples at the high clock rate, increasing internal word length requirements at each successive stage. The rate converter downsamples the accumulated sequence by integer factor R, passing reduced-rate samples to the differentiator section. Differentiator stages compute finite differences at the lower sampling clock frequency.
Bit width must expand at each stage to accommodate total growth, calculated as the product of filter order and the logarithm base two of the decimation factor.
Passband Droop
Magnitude response features a wide main lobe accompanied by periodic nulls at multiples of the decimated sampling frequency. High-frequency aliasing components fold into the passband near these attenuation nulls, degrading signal-to-noise ratio. Signal attenuation within the passband, known as passband droop, requires secondary compensation filtering using finite impulse response structures.
Compensation filters restore flat frequency response over the operational bandwidth while suppressing residual aliasing energy.
Decimation Boundary
Filter stage count determines maximum attenuation slope outside the passband for decimation applications.
