DFE Tap Coefficient Scaling for Nonlinear Distortion Compensation
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Solution Overview
Problem
High-speed digital communication receivers face significant nonlinear distortion due to amplifier saturation, leading to suboptimal adaptation and high bit error rates, particularly in backplane bus systems, where the 1 dB compression point is approached as data rates exceed 2 Gbps, necessitating attenuation to prevent distortion but reducing noise immunity.
Innovation Solution
A method involving a decision feedback equalizer (DFE) and an analog front end (AFE) that adapts to input signals at a first amplitude level insufficient to cause distortion, then scales coefficients and adjusts the amplitude to a higher level, allowing the receiver to operate effectively without significant nonlinear distortion, while maintaining noise immunity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the input signal amplitude is increased to improve signal strength and noise immunity, then the noise immunity improves, but nonlinear distortion occurs due to amplifier saturation
Solution Approach 1:
The DFE adapts to the input signal characteristics before the signal reaches the amplifier saturation point. By performing adaptation at a lower amplitude level where the amplifier operates linearly, the system prepares the equalizer coefficients in advance to handle the signal characteristics, then these coefficients can be used when higher amplitude signals are received without causing distortion
Solution Approach 2:
The system changes the operating parameters of the DFE adaptation process by using a lower amplitude input signal during the adaptation phase compared to the normal operating phase. This parameter change allows the amplifier to remain in its linear region during coefficient training, preventing nonlinear distortion while still enabling proper equalization adaptation
2Object-affected harmful factors
If the input signal amplitude is attenuated to prevent nonlinear distortion, then the nonlinear distortion is reduced, but the noise immunity deteriorates
Solution Approach 1:
The system performs preliminary adaptation at a safe, lower amplitude level to establish optimal equalizer coefficients before actual high-amplitude signal reception occurs. This preliminary action at reduced amplitude prevents distortion during the adaptation phase while the established coefficients then enable proper handling of full-amplitude signals during normal operation
3Productivity
If the data rate is increased to improve communication speed, then the productivity increases, but the amplifier approaches its 1 dB compression point causing nonlinear distortion
Solution Approach 1:
The DFE performs preliminary adaptation to the signal characteristics at the higher data rate before the amplifier is stressed to its compression point. By adapting the equalizer coefficients in advance at the required high data rate, the system ensures optimal equalization is in place before nonlinear distortion becomes problematic, enabling sustained high-speed operation
Data Source
AI summary
A receiver has an input and a decision feedback equalizer (DFE). The DFE couples to the receiver input and has at least one tap coefficient. An input signal, having a first amplitude level insufficient to cause significant non-linear distortion in the receiver, is applied to the receiver input. After the DFE adapts to the applied input signal having the first amplitude level by adjusting the at least one tap coefficient, the adaptation process is stopped. Then the at least one tap coefficient is scaled by a factor α and the amplitude of input signal is adjusted to a second amplitude level greater than the first amplitude level by the scale factor α. Although the second amplitude level might be sufficient to cause significant non-linear distortion in the receiver, the scaled tap coefficient has the correct values for proper DFE operation in the presence of the non-linear distortion.