Post-Distortion Filter Reducing VGA Nonlinearity Sensitivity
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Solution Overview
Problem
Digital communication systems face Bit Error Rate (BER) degradation due to nonlinearities introduced by Variable Gain Amplifiers (VGAs), particularly in receivers, which are exacerbated by signals with high peak-to-average ratios, leading to sensitivity issues and suboptimal performance.
Innovation Solution
The Post-Distortion Decision Feedback Equalizer (PDFE) addresses this by incorporating a feedforward signal from the VGA to the Decision Feedback Equalizer (DFE), allowing the DFE to adjust its filtering based on the VGA's nonlinearity status, using a signal strength indicator to select between different coefficient values for improved equalization during compression and linear operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If Variable Gain Amplifier (VGA) is used to amplify signals, then signal gain is improved, but nonlinearity and sensitivity to nonlinearities increase
Solution Approach 1:
The patent feeds the amplified output signal from the VGA back to the DFE, allowing the equalizer to learn and compensate for the nonlinear distortion introduced by the amplifier. The harmful nonlinearity is converted into useful information that enables correction of the distortion, improving both gain utilization and signal accuracy.
Solution Approach 2:
The patent implements a feedback loop where the VGA output is fed to the DFE, which then processes the signal with adaptive filtering. This feedback mechanism allows the system to continuously adjust and compensate for nonlinearities, reducing sensitivity to VGA nonlinearity while maintaining high signal gain.
2Power
If signal amplification is increased to handle high peak-to-average ratio signals, then signal coverage is improved, but Bit Error Rate degradation increases
Solution Approach 1:
The patent uses the DFE to learn the nonlinear distortion characteristics from the VGA output and convert this harmful distortion into correctable information. By adapting the filter coefficients based on the amplified signal, the system can maintain high amplification while correcting the resulting BER degradation through adaptive equalization.
Solution Approach 2:
The patent dynamically changes the DFE filter coefficients based on the input signal characteristics and VGA operating conditions. This parameter adaptation allows the system to optimize performance for different signal levels and nonlinearities, maintaining low BER even with high signal amplification required for high peak-to-average ratio signals.
3Device complexity
If simpler VGA designs are used, then device complexity is reduced, but sensitivity to nonlinearities increases
Solution Approach 1:
The patent introduces the DFE as an intermediary component between the simple VGA and the signal processing chain. This mediator learns and compensates for the nonlinearities introduced by the simplified VGA, allowing the use of less complex amplifier designs while maintaining signal integrity through adaptive equalization.
Solution Approach 2:
The feedback loop from VGA output to DFE enables continuous compensation for nonlinearities. This feedback mechanism allows simpler VGA designs to achieve the required performance by relying on the adaptive equalizer to correct their inherent nonlinear distortions, reducing overall system complexity while maintaining signal quality.
Data Source
AI summary
Methods and apparatus for reducing sensitivity to nonlinearities in the receiver of a digital communications system are disclosed. One aspect can be referred to as a Post-Distortion Decision Feedback Equalizer (PDFE). A gain stage is often implemented as a variable gain amplifier (VGA), and can introduce significant nonlinearities, a problem exacerbated by signals with a large peak-to-average ratio (PAR). One embodiment provides feed forward information from the VGA regarding its status to a DFE, and the DFE adjusts its filtering based on the provided information. The advantages are also applicable to fixed-gain amplifiers and to transversal filters.