Waveform Equalizer Step-Size Control for Stable Tap Convergence
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Solution Overview
Problem
Waveform equalizers with FIR and IIR filters can experience wrong convergence of tap coefficients due to post-ghost interference, degrading their waveform equalizing capability.
Innovation Solution
A waveform equalizer with an FIR filter, an IIR filter, an adding section, an error detecting section, and a tap coefficient updating section, where the step size for updating FIR filter coefficients is set smaller than that for IIR filter coefficients initially, allowing IIR filter coefficients to converge earlier and preventing wrong convergence of FIR filter coefficients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the step size for updating FIR filter tap coefficients is set equal to or larger than that of IIR filter, then convergence speed of FIR filter is improved, but wrong convergence occurs due to post-ghost interference
Solution Approach 1:
The IIR filter is given priority in the convergence process by assigning it a larger step size during the initial period. This preliminary action allows the IIR filter to suppress post-ghost interference first, creating a cleaner signal environment before the FIR filter begins its convergence, thereby preventing wrong convergence of FIR tap coefficients
Solution Approach 2:
The step sizes for FIR and IIR filters are made dynamic rather than static. During the initial period, the IIR filter uses a larger step size for faster convergence and ghost suppression, while the FIR filter uses a smaller step size to avoid wrong convergence. After the predetermined period expires, both filters use equal step sizes for joint optimization, adapting the update strategy based on the convergence stage
2Reliability
If the step size for updating FIR filter tap coefficients is set smaller than that of IIR filter, then wrong convergence is prevented, but convergence speed of FIR filter decreases
Solution Approach 1:
The update process is divided into two distinct periods: an initial period where the FIR filter uses a smaller step size to prevent wrong convergence, and a subsequent period where both filters use equal step sizes for optimized convergence. This periodic adjustment of step size strategy ensures reliable convergence while maintaining overall efficiency
3Device complexity
If both FIR and IIR filter tap coefficients are updated with the same step size, then circuit complexity is reduced, but wrong convergence of FIR coefficients occurs
Solution Approach 1:
The tap coefficient update process is segmented into two phases: initial update period and normal update period. During the initial period, different step sizes are applied to FIR and IIR filters to prevent wrong convergence. This segmentation of the update process allows complex differential control when needed while keeping the overall system manageable
Data Source
AI summary
Tap coefficients of an FIR filter are prevented from converging to wrong values. A waveform equalizer for performing waveform equalization of an input signal and outputting a waveform equalization result as an output signal includes: an FIR filter for performing a convolution operation between the input signal and a plurality of tap coefficients; an IIR filter for performing a convolution operation between the output signal and a plurality of tap coefficients; an adding section for adding an operation result of the FIR filter and an operation result of the IIR filter and outputting an addition result as the output signal; an error detecting section for detecting an error of the output signal; and a tap coefficient updating section for updating respective tap coefficients of the FIR filter and the IIR filter based on the error. The tap coefficient updating section sets a step size for updating the tap coefficients of the FIR filter to a value smaller than a step size for updating the tap coefficients of the IIR filter during a period from start of operation of the waveform equalizer until a predetermined condition is satisfied.