Series MOS Varactor Circuit for Higher Self-Resonant Frequency
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Variable capacitance circuits using interdigital capacitors face challenges in achieving high self-resonant frequencies due to parasitic inductance, which limits their effectiveness in transmitting and receiving high-frequency wireless signals like millimeter waves.
Innovation Solution
A variable capacitance circuit is designed with a capacitor unit comprising semiconductor elements, such as transistors or diode pairs, connected in series, where the capacitance value is adjustable via a bias voltage applied by a bias circuit, and a reactive element is connected in series or parallel to the capacitor unit to enhance resonant frequency and impedance control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If interdigital capacitors are used in variable capacitance circuits, then manufacturing precision is improved, but self-resonant frequency is limited due to parasitic inductance
Solution Approach 1:
The patent changes the fundamental parameter of the capacitor structure by transitioning from interdigital capacitors to MOS transistor-based capacitors. This parameter change eliminates the parasitic inductance issue inherent in interdigital structures while maintaining manufacturing precision through standard semiconductor fabrication processes.
Solution Approach 2:
The patent substitutes the mechanical/metallic finger structure of interdigital capacitors with a semiconductor-based MOS transistor structure. This substitution replaces the physical metallic fingers that create parasitic inductance with a semiconductor device that achieves capacitance through electrical field control, thereby eliminating the harmful inductive effect.
2Speed
If high frequency wireless signals are transmitted or received, then communication performance is improved, but parasitic inductance limits the effectiveness
Solution Approach 1:
The patent converts the harmful parasitic inductance of interdigital capacitors into a beneficial structure by using MOS transistors where the gate structure naturally provides capacitance without significant parasitic inductance. The semiconductor structure itself becomes the source of useful capacitance rather than being a limitation.
Solution Approach 2:
The patent employs composite semiconductor structures combining MOS transistors with reactive elements to create a variable capacitance circuit that operates effectively at high frequencies. The combination of semiconductor materials and reactive elements achieves both variable capacitance and low parasitic inductance.
3Reliability
If additional ESD protection circuits are added, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent makes the MOS transistor serve multiple functions: it provides variable capacitance for frequency tuning and simultaneously acts as an inherent ESD protection element. This multi-functionality eliminates the need for separate ESD protection circuits, reducing overall device complexity while maintaining reliability.
Solution Approach 2:
The variable capacitance circuit structure itself provides ESD protection without requiring external protection components. The MOS transistor's inherent structure and operation mode enable it to protect against electrostatic discharge while performing its primary capacitance function, making the system self-protecting.
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 achieves a higher self-resonant frequency and lower parasitic resistance, enabling efficient transmission and reception of high-frequency wireless signals without the need for additional ESD protection circuits, while allowing for fine-tuned capacitance adjustments.
Implementation Method 1
a capacitor unit including plural semiconductor elements connected in series, the plural semiconductor elements each having a capacitance value based on a bias voltage applied thereto
Implementation Method 2
a reactive element connected to the capacitor unit... achieves a higher self-resonant frequency
Data Source
AI summary
To achieve higher self-resonant frequency and lower parasitic resistance of a variable capacitance circuit whose capacitance value is changeable. The variable capacitance circuit includes a capacitor unit, a reactive element, and a bias circuit. The capacitor unit inside the variable capacitance circuit includes plural semiconductor elements connected in series, the plural semiconductor elements each having a capacitance value based on a bias voltage applied thereto. Further, the reactive element inside the variable capacitance circuit is connected to the capacitor unit. The bias circuit inside the variable capacitance circuit applies a bias voltage to each of the plural semiconductor elements.