Optical Transmitter Cross-Point Shifting With Balanced Transconductors
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Solution Overview
Problem
Electrical-to-optical converters introduce distortion into optical signals, degrading the performance of optical transceivers due to unbalanced cross-point shifting, which affects the quality of the optical signal.
Innovation Solution
An integrated circuit with multiple differential transconductors having common polarity outputs coupled together to shift the cross-point of a signal, maintaining balanced positive and negative polarities, thereby reducing distortion introduced by subsequent stages of the optical transmitter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If cross-point shifting is applied to correct distortion in electrical-to-optical converters, then signal quality improves, but circuit complexity increases due to multiple differential transconductors
Solution Approach 1:
The cross-point shifting circuit is divided into multiple differential transconductors (first, second, third, and fourth transconductors) that process different components of the signal. Each transconductor handles specific differential pairs, allowing the complex distortion correction function to be segmented into manageable units that can be independently optimized and controlled.
Solution Approach 2:
The outputs of multiple differential transconductors are combined through current summation at common nodes. The first and second transconductors process one polarity while the third and fourth process the opposite polarity, and their outputs are merged to produce the final corrected signal, reducing the overall complexity compared to using a single complex transconductor.
2Reliability
If multiple differential transconductors with common polarity outputs are used, then distortion is reduced and signal quality improves, but manufacturing precision requirements increase
Solution Approach 1:
The circuit deliberately creates asymmetric current paths for positive and negative polarities through the differential transconductors. By using separate transconductors for each polarity group and combining them through differential signaling, the design compensates for manufacturing variations by allowing independent adjustment of each transconductor's characteristics.
Solution Approach 2:
The invention allows independent adjustment of transconductance parameters for each differential transconductor. By changing the effective transconductance values through bias current control and device sizing, the circuit can compensate for manufacturing tolerances and achieve precise cross-point shifting despite variations in component parameters.
Data Source
AI summary
This disclosure describes techniques for shifting the cross-point of a digital signal in an optical transmitter. The cross-point shifting techniques may use multiple differential transconductors with their common polarity outputs coupled together to shift the cross-point of a signal. Using multiple differential transconductors in this manner may increase the balance between the positive and negative polarities of the resulting cross-point shifted signal relative to other types of cross-point shifting techniques, which may improve the quality of an optical signal generated by an optical transmitter.