Characterizing Dynamic Front End Filter Group Delay Mismatches across Dual Sourced Commercial Sensors
Unstated front-end filter group delay mismatches across dual-sourced sensors create dynamic phase errors that destabilize real-time fusion loops.
Anti Aliasing Filter Poles
Filter Topology
Electrical circuits configured as low pass barriers define the frequency attenuation curve of an analog system before digitization. Anti aliasing filter poles determine the rate at which the signal amplitude rolls off beyond the designated corner frequency. Passive or active components arranged in successive stages create these mathematical roots in the transfer function of the circuit.
Each pole adds negative twenty decibels per decade of attenuation to the stopband performance. A designer selects the quantity and placement of these elements to ensure that high frequency noise does not fold into the lower frequency spectrum during sampling.
Response Roll-off
High order responses achieve a sharper transition between the passband and the stopband. Engineers calculate the required number of anti aliasing filter poles to meet the attenuation specifications set by the resolution of the analog to digital converter. Lower pole counts result in a gradual slope that allows out of band signals to alias into the data stream.
High pole counts increase the complexity of the hardware and introduce phase distortion near the cutoff region. Accuracy depends upon the tight tolerance of the capacitors and resistors that determine the location of every root in the complex plane.
Systemic Interaction
Operational stability within the signal chain remains sensitive to the distribution of these components. Anti aliasing filter poles create a phase lag that increases with the total order of the filter. Signal integrity suffers when the cumulative phase shift alters the timing of the captured waveform.
Manufacturers specify the maximum phase deviation permitted for critical measurement applications. Proper selection of the damping factor for each stage prevents peaking in the frequency response that would otherwise distort the captured data.
Performance Boundaries
Environmental factors introduce shifts in the center frequency that influence the efficacy of the filtering process. Thermal expansion of the dielectric material in capacitors changes the values that fix the location of anti aliasing filter poles. Calibration procedures must account for these drifts to maintain the prescribed sampling integrity across the full operating range of the sensor.
Variations in the input impedance of the subsequent digitization stage also load the filter and shift the pole positions away from their design points. Precise control of the component environment dictates the ultimate precision of the signal reconstruction.