Adaptive Equalization Circuit Noise Application for Tap Convergence
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Solution Overview
Problem
In digital coherent receivers, the tap coefficient of adaptive equalization circuits fails to converge within the number of taps during fractional sampling, leading to a decrease in accuracy of compensation for transmission line characteristics.
Innovation Solution
An adaptive equalization circuit that includes a butterfly FIR filter, a filter coefficient update control unit, and a noise applying unit, which applies noise outside the signal band to the input signals to generate a tap coefficient that attenuates outside the bands, allowing the tap coefficient to converge within the number of taps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If fractional sampling is used in adaptive equalization circuits, then the sampling rate is increased, but the tap coefficient fails to converge within the number of taps
Solution Approach 1:
The patent applies preliminary action by pre-processing the input signal through a noise applying unit that adds artificial noise before the signal enters the adaptive equalization circuit. This preliminary noise application shapes the spectral characteristics of the input signal, ensuring that the tap coefficient can properly converge even during fractional sampling operations, thereby maintaining compensation accuracy at higher sampling rates.
2Measurement precision
If the number of taps is increased to improve convergence, then the compensation accuracy improves, but the device complexity increases
Solution Approach 1:
The patent applies parameter changes by modifying the spectral parameters of the input signal through noise application, rather than changing the structural parameter of the number of taps. By adding artificial noise with specific spectral characteristics, the system achieves proper tap coefficient convergence without increasing the number of taps, thus maintaining compensation accuracy while avoiding increased device complexity.
3Reliability
If noise is applied outside the signal band, then the tap coefficient converges properly, but the signal processing complexity increases
Solution Approach 1:
The patent introduces an intermediary element - artificial noise - that mediates between the input signal and the adaptive equalization circuit. This noise component serves as a spectral shaper that improves convergence reliability without requiring complex processing changes to the main signal path. The noise is applied in a simple additive manner outside the signal band, maintaining processing simplicity while achieving reliable convergence.
Data Source
AI summary
An adaptive equalization circuit includes: a first filter configure to perform filtering on an input signal based on a tap coefficient; an applying circuit configured to apply, to the signal, noise outside a band of the signal; and a controller configured to set, for the first filter, the tap coefficient that compensates for transmission line characteristics of the signal, based on the signal to which the noise is applied by the applying circuit.