CMOS Switch Linearizer Using a Varactor for Off-State Distortion
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Solution Overview
Problem
Conventional CMOS switches in antenna tuning circuits face limitations due to nonlinear capacitance in the off-state, leading to distortion and noise issues, which existing methods such as using CMOS silicon on insulator or stacking FETs have not adequately addressed, resulting in limited linearity improvements and additional loss.
Innovation Solution
The implementation of a switch coupled with a linearizer, specifically a varactor, which generates third-order distortion of equal magnitude and opposite phase to cancel out the distortion produced by the switch in the off-state, thereby improving linearity and reducing unwanted distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional CMOS switches are used in antenna tuning circuits, then the circuit can be implemented with standard technology, but the nonlinear capacitance in off-state causes distortion and poor linearity
Solution Approach 1:
The patent converts the harmful nonlinear capacitance effect into a beneficial linearizing mechanism by introducing a varactor whose nonlinear capacitance characteristic is specifically designed to cancel the switch's nonlinear capacitance. The varactor's capacitance varies with voltage in a way that compensates for the switch's nonlinear behavior, transforming the problem of nonlinear capacitance into a solution for linearity improvement.
Solution Approach 2:
The varactor acts as an intermediary element between the switch and the rest of the antenna tuning circuit. It mediates the nonlinear capacitance effect by introducing an opposing nonlinear characteristic that cancels the harmful distortion, allowing the switch to operate with improved linearity without requiring fundamental changes to the switch design itself.
2Manufacturing precision
If CMOS silicon on insulator or stacked FETs are used to enhance linearity, then some linearity improvement is achieved, but additional loss is introduced and results are limited
Solution Approach 1:
The patent changes the operational parameters of the switch-circuit system by introducing a voltage-controlled varactor element. By dynamically adjusting the varactor's capacitance parameter in response to the switch's nonlinear behavior, the system achieves linearity improvement without the structural modifications and associated losses of SOI or stacked FET approaches. The parameter change occurs through voltage control rather than physical restructuring.
3Manufacturing precision
If multiple FETs are stacked in series to reduce individual FET voltage swings, then linearity is slightly improved, but device complexity and loss increase
Solution Approach 1:
The patent extracts the linearity improvement function from the switch structure itself and places it in a separate, dedicated varactor component. Instead of making the switch more complex through stacking or SOI structures, the solution separates the switching function from the linearity compensation function, allowing each to be optimized independently and reducing overall device complexity.
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 approach effectively cancels third-order distortion, enhancing the linearity of the switch in the off-state, thereby improving the performance of antenna tuning circuits by reducing spectral emissions and maintaining low receiver noise, while also minimizing additional loss and maintaining reliability.
Implementation Method 1
a linearizer coupled to the switch, the linearizer configured to cancel at least a portion of third-order distortion generated by the switch
Data Source
AI summary
Exemplary embodiments are related to switch linearizer. A device may include at least one switch. The device may further include a linearizer coupled to the at least one switch and configured to cancel at least a portion of distortion generated by the at least one switch in an off-state.