Class-AB Line Driver With Common-Mode Termination for Low Distortion
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Solution Overview
Problem
Automotive Ethernet line drivers face challenges in achieving high linearity while maintaining power efficiency and reducing common mode signals, which are critical for intra-vehicular data communication in vehicles.
Innovation Solution
A class-AB line driver circuit is designed with integrated common mode termination and differential input stages, eliminating level shifting circuitry to reduce distortion and provide precise quiescent current control, while using amplifiers to drive output transistors and incorporating a common mode termination network to minimize common mode signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If class-AB output stage is used to improve power efficiency, then power consumption is reduced, but linearity performance deteriorates
Solution Approach 1:
The line driver is divided into two separate differential input stages (first and second) that operate in parallel, with each stage contributing to the overall output. This segmentation allows the circuit to maintain class-AB power efficiency while improving linearity through the combined effect of multiple stages, resolving the contradiction between power efficiency and linearity performance.
Solution Approach 2:
The patent implements precise quiescent current control by adjusting biasing parameters in the class-AB output stage. By optimizing the quiescent current level and the timing of current transitions between classes A and B operation, the circuit achieves better linearity performance while maintaining power efficiency advantages of class-AB operation.
2Adaptability or versatility
If level shifting circuitry is included to improve signal level matching, then signal compatibility is improved, but distortion increases
Solution Approach 1:
The patent removes the level shifting circuitry from the signal path entirely. Instead of adding level shifting functionality that introduces distortion, the design relies on the inherent capability of the differential input stages and class-AB output stage to provide appropriate signal level matching, thereby eliminating the source of distortion while maintaining signal compatibility.
3Device complexity
If common mode termination is not integrated to simplify the circuit, then device complexity is reduced, but common mode signals increase
Solution Approach 1:
The common mode termination network is integrated directly into the line driver circuit, merging the termination function with the existing output stage components. This integration provides effective common mode signal suppression without adding separate discrete termination components, thus reducing overall device complexity while minimizing common mode emissions.
Data Source
AI summary
A line driver circuit includes a first input terminal, a second input terminal, a first input stage, a second input stage, a first output stage, and a second output stage. The first input stage includes a first input coupled to the first input terminal, and a second input coupled to the second input terminal. The second input stage includes a first input coupled to the first input terminal, and a second input coupled to the second input terminal. The first output stage includes a first input coupled to a first output terminal of the first input stage and a second input coupled to a first output terminal of the first input stage. A second output stage includes a first input coupled to a second output terminal of the first input stage and a second input coupled to a second output terminal of the first input stage.