Phase Compensation Architectures for Asynchronous Decimation Delays in Multirate Feedback Loops
Dynamic Farrow filters and state observers restore feedback phase margin by compensating time-varying asynchronous decimation group delays in real time.
Decimation Latency Jitter
Timing Variance
Digital signal acquisition architectures employ multi-rate filtering stages to reduce oversampled sensor converter streams to baseband sample rates. In synchronous sigma-delta converters and digital audio instrumentation, decimation latency jitter represents the cycle-to-cycle variation in the propagation delay between the raw analog-to-digital modulator sampling instant and the appearance of the decimated word at the output register. The definition ceases at asynchronous sampling boundaries where output timing is governed by independent downstream system clocks.
Filter Architecture
Cascaded integrator-comb filters and polyphase finite impulse response decimation blocks possess fixed algorithmic group delays determined by filter tap lengths and downsampling factors. However, decimation latency jitter arises when downsampling reset counters slip phase relative to external synchronization pulses, or when internal clock dividers experience phase jitter. Variable pipeline flushing in shared digital signal processing cores also introduces execution timing variations.
If decimation clock signals share logic gates with asynchronous switching traffic, cross-talk and power supply bounce modulate internal propagation thresholds. Maintaining strict integer downsampling synchronization locks the algorithmic delay to a fixed integer multiple of modulator clock cycles.
Measurement Degradation
Fluctuations in filter output latency degrade phase coherence in multi-channel phased array systems and distributed current sensors. In feedback control loops, latency jitter manifests as phase noise that reduces stability margins at higher bandwidths. Simultaneous sampling across parallel converter channels becomes corrupted when individual decimation pipelines suffer differential delay jitter.
This time-stamp uncertainty undermines sensor fusion calculations in multi-axis motion sensing platforms.
Jitter Characterization
Time-interval analyzers quantify delay variance by triggering on an input analog step function and timing the subsequent output data-ready strobe over millions of acquisition cycles. Calibration engineers measure histogram distributions of latency spread to isolate deterministic clock division skew from random thermal jitter. Compliance testing verifies that decimation timing variations remain within picosecond boundaries before sensor modules receive field certification.