Retiming Techniques for IIR Filters Retiming refers to the process of adjusting the phase and/or group delay of an IIR filter to achieve the desired perf...
Retiming refers to the process of adjusting the phase and/or group delay of an IIR filter to achieve the desired performance characteristics. This is particularly important in pipeline and parallel processing, where the filter architecture is built from multiple interconnected components with varying delays.
There are two main retiming techniques commonly used for IIR filters:
1. Phase Shifters:
Shift the phase of each IIR filter tap by the appropriate amount to compensate for the different delays introduced by subsequent filters in the pipeline.
This can be achieved by adding or subtracting delays within the pipeline.
2. Group Delay Compensation:
Adjust the group delay of each tap to ensure that the output of one tap reaches the input of the next tap at the correct phase.
This is achieved by adding or subtracting delays within the group itself.
Examples:
Phase Shifters: In a 4-tap pipeline, shifting the phase of the second and fourth taps by 180° relative to the first and third taps can compensate for the different delays caused by the 2-tap pipeline segments.
Group Delay Compensation: In a 4-tap parallel processing structure, adjusting the group delay of the first and third taps to match the group delay of the second and fourth taps can ensure that the outputs are synchronized.
Benefits of Retiming:
Improves the overall system performance by reducing the impact of pipeline/parallel processing delays on filter accuracy.
Allows for better utilization of available resources by ensuring that all filters operate with the same phase and delay.
Provides flexibility in customizing the filter response by adjusting the phase or group delay of individual taps.
Additional Notes:
Retiming can be applied not only to individual taps but also to the entire IIR filter itself.
The specific retiming technique chosen depends on the individual filter architecture, the desired performance characteristics, and the available resources