Differential Varactor Control Using Same-Type Transistor Paths
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Solution Overview
Problem
Conventional voltage-controlled variable capacitor devices exhibit undesirable properties such as sharp capacitance-to-control voltage transfer curves, leading to gain non-uniformity and immunity issues due to poor matching between complementary transistor devices, and lack a mechanism for independent control of differential and common mode gains.
Innovation Solution
The implementation of voltage-variable resistor tuned capacitor architectures with differential control using transistors of the same doping type, allowing for uniform and symmetric transfer characteristics, and independent tuning of common mode and differential mode gains through separate control terminals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If complementary NFET and PFET devices are used for differential control of varactor, then differential control capability is achieved, but matching between transistors deteriorates under process and temperature variation
Solution Approach 1:
The patent uses two NFET devices (or two PFET devices) of the same transistor type instead of complementary NFET and PFET devices. This homogeneity ensures that both transistors exhibit identical electrical characteristics and respond uniformly to control voltages, eliminating matching issues under process and temperature variations while maintaining differential control capability.
2Productivity
If conventional varactor architecture is used, then basic capacitance tuning is achieved, but transfer characteristics exhibit sharp transitions leading to gain non-uniformity
Solution Approach 1:
The patent introduces a second control dimension by applying control voltages to both the gate and bulk terminals of the NFET devices. This dual-terminal control enables independent adjustment of capacitance and transconductance, providing an additional degree of freedom to linearize the transfer characteristics and achieve uniform gain across the tuning range.
Solution Approach 2:
The patent changes the electrical parameters of the NFET devices by applying specific control voltages to both gate and bulk terminals. This dynamic parameter adjustment allows optimization of the capacitance-voltage relationship to achieve linear transfer characteristics, and enables independent control of differential and common-mode gains for improved performance.
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 enhances the linearity of frequency tuning and reduces gain variation in oscillator circuits, providing improved performance and immunity to common mode noise by eliminating the need for complementary transistor pairs and allowing precise control of varactor gains.
Implementation Method 1
first and second transistors are configured as voltage variable resistors for tuning a capacitance of the variable capacitor device
Data Source
AI summary
A variable capacitor device comprises first and second control paths which are configured to enable differential control using first and second transistors of a same doping type in the first and second control paths, respectively, wherein the first and second transistors are configured as voltage variable resistors for tuning a capacitance of the variable capacitor device.