Decision Feedback Equalizer Precursor ISI Reduction
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Solution Overview
Problem
Existing decision feedback equalization (DFE) techniques, such as feed-forward equalization (FFE), face limitations in reducing precursor inter-symbol interference (ISI) as they can amplify noise and crosstalk, necessitating an improved method for effective precursor ISI reduction in integrated circuit (IC) devices.
Innovation Solution
The proposed solution involves an enhanced decision feedback equalizer (EDFE) with a precursor cancellation block that uses a comparison and selection circuit to subtract weighted postcursor decisions from the analog input signal, comparing the signal against various threshold inputs to select the appropriate digital output, thereby reducing precursor ISI while minimizing noise and crosstalk amplification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If feed-forward equalization (FFE) is used to reduce precursor ISI, then precursor ISI reduction is achieved, but noise and crosstalk are amplified
Solution Approach 1:
The patent employs decision feedback equalization (DFE) where decisions made on previous symbols are fed back to cancel their interference on current symbols. The postcursor decisions are subtracted from the analog input signal to reduce precursor ISI without the noise amplification problem of FFE, as the feedback mechanism uses already-decoded information to predict and cancel interference.
Solution Approach 2:
The patent extracts and separates the postcursor interference component from the received signal by identifying and subtracting the weighted postcursor decisions from the analog input signal. This isolation allows precise cancellation of the harmful precursor ISI while leaving the desired signal and noise components unaffected.
2Object-affected harmful factors
If multiple comparators and selection circuits are added to implement precursor cancellation, then precursor ISI reduction improves, but device complexity increases
Solution Approach 1:
The patent divides the equalization function into separate blocks: a subtraction block for postcursor cancellation, a postcursor decision block for generating decisions, and a precursor cancellation block with comparators for threshold-based selection. This segmentation allows each block to perform a specific function efficiently, reducing overall system complexity while achieving effective precursor ISI reduction.
Solution Approach 2:
The patent uses dynamic threshold selection where the comparison thresholds are adaptively determined based on the postcursor coefficient h1 and precursor coefficient hm1. The selection circuit dynamically chooses among multiple threshold inputs (-h1-hm1, +h1-hm1, -h1+hm1, +h1+hm1) based on the current signal conditions, allowing the system to optimize performance without requiring a fixed complex circuit structure.
Data Source
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AI summary
In a receiver (100), a decision feedback equalizer (120) provides weighted postcursor decisions (121) to a subtraction block (122) for subtraction from an analog input signal (101) to provide an analog output signal (123). A postcursor decision block (130) compares the analog output signal (123) against positive and negative values (104, 105) of a postcursor coefficient for providing first and second possible decisions (136, 137) for selecting a current postcursor-based decision (116) therebetween responsive to a previous postcursor-based decision (117). A precursor cancellation block (108) receives the analog output signal (123), the previous postcursor-based decision (117) and the current postcursor- based decision (116) for providing a digital output signal (124) for a previous sample of the analog input signal (101). The precursor cancellation block (108) includes comparators (211 -214) for receiving the analog output signal (123) and for respectively receiving threshold inputs (201 -204) different from one another for providing possible digital outputs (215-218) for the analog output signal (123). The selection stage (230) is coupled for receiving the possible digital outputs (215-218) for selection of the digital output signal (124).