Current-Controlled Variable Inductor Circuit for High-Frequency Tuning
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Solution Overview
Problem
Conventional variable inductor circuits for high-frequency applications are costly due to the need for a DC voltage source around 20 V to adjust inductance, making them unsuitable for cost-effective use in high-frequency bands.
Innovation Solution
A variable inductor circuit with a cascode amplifier and a control current source, where a high-frequency voltage is applied through a buffer or limiting amplifier to control the current in magnetically coupled inductors, allowing for adjustable inductance without the need for high DC voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a varactor diode is used to change the apparent Cgs in a variable inductor circuit, then the inductance value can be adjusted in high frequency band, but a DC voltage source around 20 V is necessary which increases mounting cost
Solution Approach 1:
The patent changes the control parameter from voltage-based (varactor diode requiring 20V DC) to current-based (control current source). By using a cascode amplifier where the control current source adjusts the current through the second transistor, the inductance is varied through current modulation rather than voltage modulation, eliminating the need for high voltage DC sources and reducing mounting cost
Solution Approach 2:
The patent replaces the voltage-controlled varactor diode mechanism with a current-controlled cascode amplifier mechanism. The cascode amplifier uses transistors in a specific configuration where the control current modulates the effective inductance, substituting the mechanical/electrical voltage control system with a current control system that is more cost-effective and suitable for integrated circuits
2Reliability
If conventional inductor circuits are used for impedance matching, then impedance matching can be achieved, but the inductance value cannot be easily adjusted resulting in performance deterioration when operation frequency changes
Solution Approach 1:
The patent makes the inductor dynamic by introducing a control current source that can continuously adjust the inductance value. The cascode amplifier configuration allows the effective inductance to be dynamically controlled by varying the control current, enabling the circuit to adapt to different operation frequencies and maintain optimal impedance matching performance across a wide frequency range
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 enables cost-effective electrical adjustment of inductance values in high-frequency bands, reducing mounting costs and improving the variable range of inductance while maintaining high Q values.
Implementation Method 1
a first inductor L1 and a second inductor L2 magnetically coupled to each other
Data Source
Figure 1~3
Figure 4~6
Figure 7~8
AI summary
One inductor (1a) and another inductor (1b) are magnetically coupled to each other. A variable current source (2) controls the current flowing in the one inductor (1a). By controlling the current flowing in the one inductor (1a), the inductance value of the other inductor (1b) is made variable.