MOS Capacitor Switching Circuit for Low Temperature Coefficient
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Solution Overview
Problem
Existing electronic capacitors, particularly those using metal-on-metal (MOM) capacitors, exhibit high temperature coefficients, making them impractical for precision analog circuitry due to significant variations in capacitance with temperature changes.
Innovation Solution
The implementation of metal-oxide-semiconductor (MOS) transistors configured to simulate a capacitor, with switches controlling the MOS transistors to maintain stability across temperature variations, effectively reducing the temperature coefficient to levels suitable for analog and RF applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If metal-on-metal (MOM) capacitors are used, then the capacitor structure is simple and easy to manufacture, but the temperature coefficient is high causing significant capacitance variations with temperature changes
Solution Approach 1:
The patent changes the fundamental parameters of the capacitor by transitioning from metal-on-metal construction to MOS transistor-based construction. This parameter change fundamentally alters the temperature coefficient characteristics, reducing it from high (MOM) to low (MOS), while accepting increased structural complexity as a trade-off for improved temperature stability.
Solution Approach 2:
The patent employs a composite structure combining MOS transistors with switching elements to create a simulated capacitor. This composite approach leverages the temperature-stable characteristics of MOS devices while using switches to control and optimize the overall performance, achieving low temperature coefficient through the synergistic combination of different device types.
2Reliability
If MOS transistors with switches are used to simulate a capacitor, then the temperature coefficient is significantly reduced, but the device complexity increases
Solution Approach 1:
The patent makes MOS transistors serve multiple functions: they act as both the capacitive element and the temperature-stabilizing component. By configuring MOS transistors in specific arrangements with switches, the same devices provide both capacitance and temperature compensation, reducing the need for separate components and thereby mitigating the complexity increase.
Solution Approach 2:
The patent divides the capacitor functionality into multiple MOS transistors that can be independently controlled by switches. This segmentation allows each transistor to contribute to the overall capacitance while being individually optimized for temperature stability, and enables selective activation to maintain performance across different operating conditions.
3Measurement precision
If multiple MOS transistors and switches are configured to simulate a capacitor, then precision analog and RF applications become feasible, but the circuit area increases
Solution Approach 1:
The patent merges the capacitor function with the switching control logic into a single integrated structure. By combining multiple MOS transistors and switches in a unified configuration, the design achieves precise capacitance control for analog and RF applications while minimizing the total area required compared to using separate discrete components.
Data Source
AI summary
Low temperature coefficient capacitors are described. In an embodiment, a capacitor includes several metal-oxide-semiconductor (MOS) transistors, where each of the several MOS transistors includes a gate, a source and a drain terminal, and where the source and drain terminals of each of the several MOS transistors are connected; several switches, where each of the switches includes two terminals; where first terminals of each of the switches from the several switches are connected together; and where a second terminal of each of the switches from the several switches is connected to a gate terminal of each of the several MOS transistors.