Analog Transcap Device for High-Frequency ICs
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Solution Overview
Problem
Existing semiconductor variable capacitors face limitations in achieving high capacitance density, linearity, and low distortion, especially in integrated circuits, due to process variations and the overlap of DC control voltage with AC signals, which restricts their use in high-frequency applications.
Innovation Solution
A MOS-based semiconductor variable capacitor with at least three terminals, where one terminal modulates the capacitor area through DC voltage, decoupling AC and DC signals to prevent distortion, and is designed to minimize process sensitivity, achieving high capacitance density and linearity across a wide range of control voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a two-terminal varactor is used to vary capacitance by applying DC voltage, then capacitance can be tuned, but the AC signal overlaps with the DC control voltage causing distortion
Solution Approach 1:
The patent divides the capacitor into two separate terminals: one dedicated to AC signal input and another to DC control voltage. This segmentation allows independent control of signal and bias voltage, preventing their overlap and the resulting distortion while maintaining capacitance tuning capability.
2Measurement precision
If reverse bias voltage is increased to reduce capacitance, then capacitance value decreases, but reverse-biased saturation current prevents achieving extremely high capacitance values
Solution Approach 1:
The patent changes the control mechanism from varying reverse bias voltage to varying the area of the capacitor plate through a movable contact. This parameter change allows capacitance to be varied over a wider range without being limited by reverse-biased saturation current, enabling both very high and very low capacitance values.
3Quantity of substance
If junction area is increased to maximize capacitance, then capacitance density improves, but device area increases
Solution Approach 1:
The patent introduces a movable contact that can dynamically adjust the effective area of the capacitor plate. This dynamic mechanism allows the capacitance to be varied from very small to very large values without changing the physical footprint of the device, resolving the contradiction between capacitance density and device area.
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 enhanced capacitance density, linearity, and reduced distortion, making it suitable for integrated circuits and high-frequency applications by effectively controlling capacitance without overlapping DC and AC signals.
Implementation Method 1
the synthesis of two MOS capacitor is used to obtain a good linearity over a wide range relative to the DC control voltage
Implementation Method 2
the thickness of a depletion region formed in a pn-junction diode is varied by changing a reverse bias voltage to alter the junction transition capacitance
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 avoiding 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.