Programmable Tap Decision Feedback Equalizer for Reflection Interference
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Solution Overview
Problem
Decision feedback equalizers (DFEs) face difficulties in equalizing frequency responses of received signals due to prolonged reflections of previously received signals, which interfere with the signal and hinder effective noise reduction.
Innovation Solution
The implementation of a DFE with programmable taps and a Sign Sign Least Mean Square (SSLMS) algorithm for updating tap weights, along with a comparator to selectively enable tap outputs based on impulse response thresholds, allows for adaptive adjustment of tap weights and improved noise reduction without amplifying noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a DFE is used to equalize frequency response, then the eye opening is increased, but prolonged reflections of previously received signals interfere with the signal making equalization difficult
Solution Approach 1:
The DFE is divided into multiple independent tap units (first tap unit, second tap unit, etc.), each processing specific delayed versions of the received signal. This segmentation allows selective cancellation of reflected signals at different time delays, effectively addressing the interference problem while maintaining equalization performance.
Solution Approach 2:
The DFE uses previously received signal samples (past decisions) to generate cancellation signals that are subtracted from the current received signal. This preliminary action of using past information to compensate for current interference enables the system to overcome the harmful effects of reflections before they degrade the equalization.
2Reliability
If conventional DFE structures are used, then basic equalization is achieved, but noise is amplified during the equalization process
Solution Approach 1:
Each tap unit in the DFE has locally optimized coefficients that are specifically designed to cancel reflections at particular time delays rather than applying uniform processing across all signal components. This local quality approach allows selective enhancement of signal components while suppressing noise, preventing noise amplification during equalization.
3Adaptability or versatility
If multiple tap units are added to handle prolonged reflections, then equalization capability is improved, but device complexity increases
Solution Approach 1:
Multiple tap units are merged into a unified DFE structure with a shared summer that combines the outputs of all tap units. This merging approach maintains the adaptability to handle prolonged reflections through multiple taps while reducing overall complexity by sharing common components (summer, clock signal distribution) rather than having completely separate processing chains for each tap.
Data Source
AI summary
An apparatus comprises a plurality of delay elements connected in series. Each delay element is configured to delay a respective input signal and to output a respective delayed signal. The apparatus also comprises a weight generator configured to generate a plurality of tap weights based on the delayed signals. The apparatus further comprises a tap controller configured to (1) generate tap weight enabling signals corresponding to one or more of the tap weights based on a determination that the corresponding tap weights are greater than a predetermined threshold value, and (2) generate a set of bias factors. The apparatus additionally comprises a summer configured to output a weighted signal based on the delayed signals, the tap weight enabling signals, the tap weights, and the bias factors.