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Rapid Power MOSFET Switching Circuit    

Turn-on threshold biased power MOSFET switching provides high bandwidth DC-DC voltage conversion at high efficiency.

Overview

By biasing a mosfet in a switching converter at its turn-on threshold, and modulating the threshold voltage between ON and OFF states as well, charge required to turn it to full-on is significantly minimized as is parasitic coupling capacitance at the gate node. Transitioning between inversion-threshold and full-on, at low effective switched capacitance, energy employed in switching is minimized quadratically, raising efficiency particularly at low conversion ratios and high frequencies. Applications include DC-DC converters, regulators for cell phones and other portable devices, as well as high-frequency switching voltage regulators and active noise regulators/droop suppression for microprocessor voltage domains and other point of load (POL) implementations.

Problem Solved by the Technology
Buck conversion is most efficient using switching regulators, but switching regulators have been unable to scale in bandwidth significantly, primarily due to energy losses in switching that limit higher frequency operation. Smaller form factors are enabled by higher frequencies of operation. Rapid MOSFET Switching technology applies a well-known analog technique, gate and body biasing, to switching converters, digital operation significantly reducing switch voltage transitions as well as switched effective capacitance, thereby reducing switching energy loss. This enables much higher operational frequencies and therefore much smaller form factors, and higher efficiency, critical needs for portable multimedia devices. Higher bandwidth in switching regulators permits their use in voltage domains in multi-core microprocessors. Designs such as Transient Regulation and Active Noise Regulation / Local Voltage Regulation are also enabled and rendered low cost by this technology.

Primary Application of the Technology

Traditional switching DC-DC converter designs follow digital operating principles, switching transistors ON and OFF through voltage transitions that swing over the entire driver power supply difference. This is in practice unnecessary, since a switched transistor does not turn ON until the voltage at its gate node exceeds that of its source node by at least the sum of its threshold voltage and body effect voltage. Therefore, for all practical purposes, a mosfet biased at its turn-on-threshold is effectively OFF, and this reduces the required voltage swing to turn the mosfet ON by the bias potential while maintaining the full current performance desired. Where possible, a body bias is employed that moves the turn-on-threshold closer to the full gate drive potential, thus minimizing voltage swing to turn ON. Additionally, when biased at its turn-on-threshold, a mosfet exhibits the least parasitic capacitance at its gate because of the absence of any conducting charges in the channel. Hence the energy spent, proportional to C*V^2*F, where C is the effective capacitance (that varies with applied gate voltage), V is the swing voltage, and F the frequency is minimized significantly as compared with a purely digital implementation. For low conversion ratios between input and output voltages, this provides a particularly significant energy and efficiency advantage. Because switching losses are diminished, higher frequencies are made possible.

Other Potential Applications

Low footprint Active Capacitors (Capacitors that respond proactively to reduce noise)

Competitive Advantage

- Much lower switching energy consumption
- Significantly higher performance (frequency, bandwidth)

Patent Summary

U.S. Patent Classes & Classifications Covered in this listing:

Class 327: Miscellaneous Active Electrical Nonlinear Devices, Circuits, And Systems

This is the residual class for electrical devices, circuits or systems having an output not directly proportional to its input and comprising at least one component which can provide gain or can route electrical current and which device, circuit or system does not form a complete system such as is classified specifically elsewhere or a subcombination of utility only in such elsewhere classified system.

Subclass 404: Field-effect transistor
Subclass 427: Field-effect transistor
Subclass 534: Having particular substrate biasing

Class 257: Active Solid-State Devices (E.G., Transistors, Solid-State Diodes)

This class provides for active solid-state electronic devices, that is, electronic devices or components that are made up primarily of solid materials, usually semiconductors, which operate by the movement of charge carriers - electrons or holes - which undergo energy level changes within the material and can modify an input voltage to achieve rectification, amplification, or switching action, and are not classified elsewhere.

Subclass E25.029: Devices being of two or more types, e.g., forming hybrid circuits (EPO)
Subclass E23.068: Additional leads joined to metallizations on insulating substrate, e.g., pins, bumps, wires, flat leads (EPO)
Subclass E23.079: For integrated circuit devices, e.g., power bus, number of leads (EPO)
Subclass E23.174: Conductive vias through substrate with or without pins, e.g., buried coaxial conductors (EPO)