PAM-4 CMOS Optical Interface Linearization for Equal Eye Openings
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Solution Overview
Problem
CMOS repeater/amplifier devices introduce non-linearity issues in PAM-4 signal transmission, particularly when handling high-swing electrical signals, leading to distorted PAM-4 pulse amplitude levels and increased bit-error-rate due to frequency-dependent data communication signal channel loss.
Innovation Solution
A linearity control circuit with a dual-path configuration, comprising a main and sub-path with differential amplifiers and weighting circuits, adjusts signal gains to equalize PAM-4 pulse amplitude levels by pre-distorting the signal to mitigate linearity degradation caused by CMOS repeater/amplifiers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If CMOS repeater/amplifier devices are used to handle high-swing electrical signals, then signal transmission capability is improved, but non-linearity issues occur causing distorted PAM-4 pulse amplitude levels
Solution Approach 1:
The patent applies preliminary action by pre-distorting the electrical signal before it enters the CMOS repeater/amplifier chain. The pre-distortion circuit intentionally introduces the opposite of the expected non-linearity, so that when the signal passes through the amplifier, the distortions cancel out and the PAM-4 pulse amplitude levels remain equalized at the output.
Solution Approach 2:
The patent implements feedback by monitoring the output signal from the CMOS repeater/amplifier and using this information to adjust the pre-distortion applied to subsequent signals. This closed-loop approach ensures that the pre-distortion parameters are continuously optimized to compensate for the non-linear characteristics of the amplifier, maintaining equal eye openings and reducing bit-error-rate.
2Length of stationary object
If signal gain is increased to compensate for channel loss, then transmission distance is extended, but linearity degradation occurs increasing bit-error-rate
Solution Approach 1:
The patent applies preliminary action by pre-distorting the electrical signal before it enters the CMOS repeater/amplifier chain. The pre-distortion circuit intentionally introduces the opposite of the expected non-linearity, so that when the signal passes through the amplifier, the distortions cancel out and the PAM-4 pulse amplitude levels remain equalized at the output.
Solution Approach 2:
The patent implements parameter changes by dynamically adjusting the pre-distortion parameters based on the operating conditions of the CMOS repeater/amplifier. By changing the pre-distortion characteristics in response to variations in gain and linearity, the system maintains optimal signal quality over extended transmission distances while minimizing bit-error-rate.
Data Source
AI summary
A linearity control circuit includes first and second input terminals. A first differential amplifier has a first input connected to the second input terminal and a second input connected to the first input terminal. Inputs of a first weighting circuit are respectively connected to outputs of the first differential amplifier. A second differential amplifier has a first input connected to the first input terminal and a second input connected to the second input terminal. Inputs of a second weighting circuit are respectively connected to outputs of the second differential amplifier. A summing device has a first input connected to an output of the first weighting circuit and a second input connected to an output of the second weighting circuit. An output of the summing device is an output of the linearity control circuit.