MOS Analog Switch With Dynamic Substrate Bias for Linearity
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Solution Overview
Problem
Existing analog switches suffer from non-linear operation, especially for low-amplitude signals, and require complex configurations with external voltage sources, leading to signal distortion and increased complexity.
Innovation Solution
An analog switch design utilizing a first MOS transistor with a control circuit comprising a follower-assembled MOS transistor and constant current source, along with series-assembled transistors between input and output terminals, to maintain a constant gate-source voltage and minimize threshold voltage, ensuring linear operation and simple structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If multiple MOS transistors are assembled symmetrically with external voltage sources to maintain substrate voltage, then the analog switch can operate with low voltage, but the device complexity increases
Solution Approach 1:
The patent merges the substrate connection function with the signal path by connecting the substrate directly to either the input or output terminal through which the signal passes. This eliminates the need for separate external voltage sources and constant current sources, reducing device complexity while maintaining low-voltage operation capability
Solution Approach 2:
The input and output terminals serve dual functions: they are both signal transmission paths and substrate voltage reference sources. This multi-functionality eliminates the need for dedicated external voltage sourcing components, simplifying the overall circuit configuration
2Device complexity
If the substrate voltage is fixed at a minimum value to simplify the circuit, then the device complexity decreases, but the linearity of the analog switch deteriorates for low-amplitude signals
Solution Approach 1:
The patent implements dynamic substrate voltage adjustment by automatically connecting the substrate to the higher-potential terminal (input or output) depending on the signal direction. This dynamic adaptation ensures the substrate voltage follows the signal voltage, maintaining constant gate-source voltage and threshold voltage, thereby preserving signal linearity for low-amplitude signals while keeping the circuit relatively simple
3Manufacturing precision
If the substrate voltage follows the signal voltage dynamically, then the signal linearity is improved, but the device complexity increases
Solution Approach 1:
The analog switch circuit automatically determines which terminal (input or output) has the higher voltage and connects the substrate to that terminal through inherent voltage comparison at the transistor gates. This self-service mechanism eliminates the need for external control circuits, achieving dynamic substrate voltage following while maintaining circuit simplicity
Data Source
AI summary
An analog switch including at least one first MOS transistor capable of transferring a signal from a first terminal to a second terminal; a connection circuit for bringing a substrate terminal of the first transistor to a voltage which is a function of the voltages of the first and second terminals; and a circuit for controlling a control voltage of the first transistor with the signal.