Three-Terminal MOS Variable Capacitor for Linear Tuning
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Solution Overview
Problem
Existing semiconductor variable capacitors, particularly varactors, face limitations in achieving high capacitance density, linearity, and wide control ranges due to distortion caused by overlapping DC and AC signals, and are not suitable for integrated circuits as they are sensitive to process variations and have low capacitance values.
Innovation Solution
A MOS-based semiconductor variable capacitor with three terminals, where the capacitance is modulated by varying the DC voltage of a control terminal relative to another terminal, decoupling AC and DC signals to prevent distortion and enhancing performance, while being less sensitive to process variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a reverse-biased pn-junction diode is used as a varactor to achieve variable capacitance, then the capacitance can be tuned by changing the reverse bias voltage, but the capacitance value is distorted by the superimposed AC voltage and the capacitance density remains low
Solution Approach 1:
The invention segments the capacitor structure into two independent parts: a fixed capacitor formed by a pn-junction and a variable capacitor formed by a MOS structure with a control electrode. This segmentation allows the variable capacitor to be controlled independently without affecting the fixed capacitor, thereby achieving linear capacitance variation with control voltage while maintaining high capacitance density
Solution Approach 2:
The MOS structure serves multiple functions: it provides the variable capacitance element, acts as the fixed capacitor plate, and enables electric field control through the control electrode. This multi-functionality allows the device to achieve both high capacitance density and linear tuning characteristics in a single integrated structure
2Adaptability or versatility
If a varactor is used to achieve variable capacitance, then the capacitance can be changed by adjusting the reverse bias, but the device is sensitive to process variations and has low capacitance values
Solution Approach 1:
The invention changes the control mechanism from reverse bias voltage to electric field control via a control electrode. By applying a control voltage to the control electrode, the depletion region width in the pn-junction is modulated, thereby changing the capacitance. This parameter change approach provides wider tuning range and reduced sensitivity to process variations
Solution Approach 2:
The control electrode acts as an intermediary that mediates the control of capacitance. Instead of directly adjusting the reverse bias voltage, the control electrode creates an electric field that modulates the depletion region, providing indirect and more stable control over the capacitance value, thereby reducing sensitivity to process variations
3Ease of operation
If a two-terminal varactor is used to vary capacitance by imposing DC voltage, then the capacitance can be tuned, but the AC voltage is superimposed on the DC control voltage causing distortion
Solution Approach 1:
The invention segments the control and signal paths into separate terminals. The control voltage is applied to the control electrode while the AC signal is applied between the two capacitor terminals. This segmentation prevents the AC signal from being superimposed on the DC control voltage, eliminating distortion while maintaining ease of capacitance control
Solution Approach 2:
The control electrode serves as an intermediary that separates the control function from the signal function. By using the control electrode to apply the DC control voltage independently from the AC signal path, the invention prevents signal distortion while maintaining straightforward capacitance control
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 provides a semiconductor variable capacitor with high capacitance density, quasi-linear capacitance variation over a wide range of control voltages, reduced distortion, and improved suitability for integrated circuits, addressing the limitations of existing varactors.
Implementation Method 1
the capacitance being modulated by varying the DC voltage of a control terminal with respect to another terminal to change the capacitance
Implementation Method 2
A MOS-based semiconductor variable capacitor with three terminals, where the capacitance is modulated by varying the DC voltage
Implementation Method 3
decoupling AC and DC signals to prevent distortion and enhancing performance
Data Source
AI summary
A novel semiconductor variable capacitor is presented. The semiconductor structure is simple and is based on a semiconductor variable MOS capacitor structure suitable for integrated circuits, which has at least three terminals, one of which is used to modulate the equivalent capacitor area of the MOS structure by increasing or decreasing its DC voltage with respect to another terminal of the device, in order to change the capacitance over a wide ranges of values. Furthermore, the present invention decouples the AC signal and the DC control voltage minimizing the distortion and increasing the performance of the device, such as its control characteristic. The present invention is simple and only slightly dependent on the variations due to the fabrication process. It exhibits a high value of capacitance density and, if opportunely implemented, shows a quasi linear dependence of the capacitance value with respect to the voltage of its control terminal.