Line Driver Bridge Termination for Output Impedance Tuning
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Solution Overview
Problem
Existing line drivers with on-chip termination face issues such as subjective output resistance due to process variation, nonlinear gain, and distortion caused by voltage divider effects, which affect the matching ratio and transimpedance gain.
Innovation Solution
The introduction of a bridge resistor and an adjustable series resistor circuit, which allows for independent adjustment of output resistance and eliminates the voltage divider effect, thereby improving transimpedance gain and ensuring output voltage consistency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If on-chip termination is used to reduce power consumption, then power efficiency is improved, but output resistance matching becomes difficult due to process variation
Solution Approach 1:
The patent implements a dynamic adjustment mechanism for the feedback resistor Rf, allowing its resistance value to be tuned after fabrication. This enables the output resistance ROUT to be adjusted to match the load resistance RL despite process variations, while maintaining the power efficiency benefits of on-chip termination.
Solution Approach 2:
The patent changes the parameter of the feedback resistor Rf to compensate for process variation effects. By adjusting Rf, the output resistance ROUT can be tuned to achieve proper matching with RL, resolving the manufacturing precision issue while keeping the on-chip termination structure intact.
2Adaptability or versatility
If a feedback resistor is used to control output impedance, then output resistance adjustment is enabled, but transimpedance gain is degraded due to voltage divider effects
Solution Approach 1:
The patent applies local quality by making the feedback resistor Rf adjustable independently from the output stage transistors. This allows precise control of output resistance without affecting the transimpedance gain of the main signal path, as the adjustment can be localized to the feedback network without degrading the primary amplification function.
Data Source
AI summary
A line driver includes current sources and resistors that form a bridge circuit in which a bridge resistor is connected between an internal node and ground, and a series resistor connected between the internal node and the driver's output node. The internal node is connected to receive a unit current from a first stage transistor, and the output node is connected to receive an amplified current from a second stage transistor that is N times the unit current. The bridge resistor is formed with a resistance value set such that the voltages at the internal node and the output node are equal, i.e., such that no current flows through the series resistor. The resistance value of the series resistor is thus adjustable to optimize output impedance in a manner independent of the driver's gain. An echo cancellation circuit is utilized to eliminate noise from two associated line drivers.