Distributed Amplifier Termination Using Temperature-Gradient Resistors
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Solution Overview
Problem
Wideband amplifiers face issues with parasitic capacitances in MOSFETs, leading to impedance mismatch and ripples in frequency characteristics, especially on the high-frequency side, making it difficult to achieve preferred frequency characteristics and wideband operation.
Innovation Solution
A distributed circuit using temperature-gradient resistors, where the resistance values are adjusted by changing the current applied to the resistors, ensuring symmetric voltage changes to maintain 50Ω impedance across the circuit, reducing parasitic capacitance effects and minimizing impedance deviation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If MOSFETs are used as variable termination resistors to adjust resistance values, then the resistance values can be adjusted to 50Ω, but parasitic capacitances cause impedance to drop at high frequencies, leading to deviation from 50Ω and ripples in frequency characteristics
Solution Approach 1:
The patent changes the physical state of the resistors from cold to hot state by applying current, utilizing the temperature coefficient of resistance to dynamically adjust resistance values. This allows continuous adjustment of termination resistors to maintain 50Ω impedance across different frequencies, solving the problem of fixed resistance values causing impedance mismatch at high frequencies
Solution Approach 2:
The patent transforms static termination resistors into dynamic ones by applying current to generate heat, which changes the resistance values in real-time. This dynamic adjustment capability allows the system to compensate for frequency-dependent impedance variations, maintaining optimal matching across the operating band
2Power
If MOSFETs with large current capacity are used to ensure sufficient current for termination adjustment, then the current capacity is sufficient, but the device size increases and parasitic capacitances become larger, worsening high-frequency performance
Solution Approach 1:
The patent replaces the mechanical/electronic MOSFET-based resistance adjustment mechanism with a thermal mechanism using temperature-gradient resistors. By applying current to generate heat and utilizing the temperature coefficient of resistance, the system achieves resistance adjustment without relying on MOSFET channel resistance, thereby eliminating MOSFET parasitic capacitances and reducing device size
3Manufacturing precision
If fixed termination resistors with exactly 50Ω are used, then impedance matching is perfect at design frequency, but process variation causes deviation from 50Ω, leading to multiple reflections and ripples in frequency characteristics
Solution Approach 1:
The patent implements a self-adjusting mechanism where the temperature-gradient resistors automatically adjust their resistance values by generating heat through applied current. This self-service capability allows the system to compensate for process variations and maintain 50Ω impedance matching without requiring external calibration or adjustment mechanisms
Solution Approach 2:
The patent employs a feedback mechanism where the effect of applied current on resistance value is continuously utilized to adjust and maintain optimal impedance matching. The current applied to the temperature-gradient resistors creates a feedback loop that automatically compensates for deviations from 50Ω caused by process variation
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 allows for easy adjustment of termination resistors, providing excellent frequency characteristics without ripples on the high-frequency side, enabling effective wideband operation in distributed amplifiers.
Implementation Method 1
Each of the input and output termination resistors is a temperature-gradient resistor having a temperature coefficient of resistance higher than 0
Data Source
AI summary
A distributed circuit includes: a first transmission line that has an input end to which an input signal is input; a second transmission line that has an output end from which an output signal is output; a plurality of unit cells that are disposed along the first and second transmission lines, the input terminals of the unit cells being connected to the first transmission line, the output terminals of the unit cells being connected to the second transmission line; two input termination resistors connected in parallel to an end of the first transmission line; and two output termination resistors connected in parallel to an end of the second transmission line. In the distributed circuit, at least one input termination resistor is a temperature-gradient resistor, and voltages at the two input termination resistors are changed symmetrically.