Resonant Variable Attenuator for Parasitic Capacitance Loss
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Solution Overview
Problem
Existing variable attenuators for RF signals face challenges in minimizing signal loss due to parasitic capacitance between transistor terminals, especially when transistors are turned off, which affects the attenuation performance, especially in high-frequency bands like K-band used in communication satellite systems.
Innovation Solution
The variable attenuator design incorporates a configuration with transistors and micro-strip transmission lines acting as inductors, where the resonance frequency is set within the operational frequency band, minimizing signal loss by using a parallel circuit of capacitors and inductors to achieve substantial impedance even when transistors are turned off.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If transistors are used as switching elements in the variable attenuator, then attenuation control is achieved, but parasitic capacitance between transistor terminals causes signal loss even when transistors are turned off
Solution Approach 1:
The patent introduces an inductor as an intermediary element connected in parallel with the transistor between the signal line and ground. This inductor acts as a mediator that provides an alternative current path, preventing the parasitic capacitance of the turned-off transistor from causing direct signal leakage to ground, thereby reducing signal loss while maintaining attenuation control capability
Solution Approach 2:
The patent changes the electrical parameters of the circuit by adding an inductor with specific inductance value to form a resonant circuit with the transistor's parasitic capacitance. By adjusting the inductance parameter, the resonant frequency is set to create high impedance at the operating frequency, effectively blocking the leakage path caused by parasitic capacitance and reducing signal loss
2Productivity
If transistors are turned off to minimize attenuation, then signal transmission is maximized, but parasitic capacitance creates a leak path to ground causing signal loss
Solution Approach 1:
The patent converts the harmful effect of parasitic capacitance into a beneficial one by combining it with an inductor to form a resonant circuit. The parasitic capacitance, which originally caused signal leakage, now works together with the inductor to create high impedance at the resonant frequency, blocking the leakage path and actually improving signal transmission when the transistor is turned off
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
This configuration effectively reduces signal loss to near zero when transistors are turned off, maintaining high attenuation performance across the frequency band, thereby addressing the limitations of existing attenuators.
Implementation Method 1
The transistor and the second transmission line cause a resonance frequency formed by a capacitor inherently attributed between the two current terminals of the transistor and the inductor attributed to the second transmission line
Data Source
AI summary
A variable attenuator operable in a frequency band from at least 10 GHz is disclosed. The variable attenuator includes an input port; an output port; a first transmission line connecting the input port with the output port; an attenuating unit provided between the first transmission line and the ground; and a second transmission line. The attenuating unit includes at least one transistor with two current terminals coupled with the first transmission line and ground, respectively. The second transmission line is coupled between the two current terminals of the transistor. The second transmission line is operable as an inductor in the frequency band. A feature of the variable attenuator is that the transistor and the second transmission line cause a resonance frequency within the frequency band by a capacitor between the two current terminals and the inductance of the second transmission line.