Differential Terminator Circuit With Feedback Bias Control
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Solution Overview
Problem
Conventional termination circuits in high-speed communication systems lack precision in controlling termination resistance due to process instability, temperature dependence, and power supply fluctuations, leading to inaccurate resistance values.
Innovation Solution
A differential circuit with a termination circuit that includes transistors and resistors connected in a triangular configuration, with a control unit adjusting the gate bias to maintain a preset termination resistance, independent of resistor variations and power supply fluctuations, by using a current source to equalize the medium node voltage with a reference voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a conventional termination circuit with FETs and resistors is used, then the termination resistance can be dynamically adjusted, but the resistance accuracy deteriorates due to process instability, temperature dependence, and power supply fluctuations
Solution Approach 1:
The patent implements a feedback mechanism where the operational amplifier continuously monitors the voltage at the medium node and adjusts the gate bias of the FETs accordingly. This closed-loop feedback system compensates for variations in resistor values, FET characteristics, and power supply fluctuations, maintaining precise termination resistance despite environmental changes and manufacturing tolerances
Solution Approach 2:
The patent changes the operating parameters of the FETs by dynamically adjusting their gate bias voltages through the operational amplifier. By varying the gate-source voltage, the equivalent resistance of the FETs is precisely controlled to maintain the desired termination resistance value, allowing dynamic adaptation while compensating for parameter drift
2Device complexity
If the termination circuit excludes the practical termination resistor from the feedback loop, then the circuit design is simplified, but the accuracy of the termination resistance deteriorates when transistors or resistors unbalance
Solution Approach 1:
The patent incorporates the termination resistors and FETs directly into the feedback loop of the operational amplifier. This ensures that any imbalances in transistor characteristics or resistor values are continuously detected and corrected by adjusting the gate bias, maintaining high accuracy without requiring overly complex external compensation circuits
3Adaptability or versatility
If FETs are used as variable resistors in the termination circuit, then dynamic resistance control is achieved, but resistance stability worsens due to inherent temperature dependence and process variability
Solution Approach 1:
The operational amplifier creates a closed-loop feedback system that continuously monitors the voltage distribution and adjusts the FET gate biases to compensate for temperature-dependent drift and process variability. This feedback mechanism stabilizes the effective resistance despite the inherent instability of FET parameters
Solution Approach 2:
The patent dynamically changes the gate-source voltage parameters of the FETs to counteract temperature effects and manufacturing variations. By adjusting the bias points, the FETs operate in a region that maintains stable equivalent resistance, transforming the inherently unstable devices into stable variable resistors
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution precisely controls termination resistance, reducing variations and maintaining accuracy across different conditions, thereby enhancing the reliability of high-speed communication systems.
Implementation Method 1
the feedback loop of the operational amplifier 105 and the reference unit 103
Implementation Method 2
the resistance of the transistor 102b, which is a sum of the resistance of the resistor 102b and the equivalent resistance of the transistor 102b
Implementation Method 3
The FET 102b operates as a variable resistor
Data Source
AI summary
The present invention provides a precisely controlled terminator circuit of a differential amplifier, in particular, for a differential amplifier of an optical receiver. The differential circuit, which receives a differential signal by a first input for the normal phase signal and a second input for an anti-phase signal, provides a terminator circuit comprises two resistors connected in serial between two inputs and two resistive connections each including a transistor and a resistor serially connected to the transistor and connected between respective inputs and the power supply line Vcc. The control unit, by receiving a medium potential of two resistors, provides a bias to two transistors so as to equalize the medium potential with the reference potential.