Push-Pull MOS Gate Drive for Fast High-Voltage RF Switching
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Solution Overview
Problem
Current control devices for high voltage MOS transistors used in radio-frequency alternating high voltage generators suffer from significant propagation delays, making them unsuitable for MHz switching frequencies, and existing solutions using transformers are costly.
Innovation Solution
A 'push-pull' type assembly with synchronized control of two complementary MOS transistors, utilizing an NMOS transistor with low internal impedance and a PMOS transistor controlled by a bipolar transistor in a common base assembly, along with capacitive link circuits and amplifier circuits, to achieve fast and efficient switching with minimal propagation delay.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If current control devices are used for high voltage MOS transistors, then the transistor can be controlled, but propagation delays are too great for MHz switching frequencies
Solution Approach 1:
The control device is segmented into two complementary MOS transistors (first NMOS control transistor and second PMOS control transistor) operating in a push-pull configuration. Each transistor handles one polarity of the control signal, allowing independent optimization of switching characteristics for each state and reducing overall propagation delay
Solution Approach 2:
The invention replaces traditional transformer-based control mechanisms with an unwound active component circuit using MOS transistors. This substitution eliminates the inherent delays associated with transformer coupling while achieving effective high-voltage transistor control through direct electronic switching
2Reliability
If transformers are used to apply symmetrical voltage to the gate of the high-voltage transistor, then effective blocking is achieved, but the solution becomes more expensive
Solution Approach 1:
The invention uses inexpensive unwound active components (MOS transistors, capacitors, resistors) instead of expensive transformers. The MOS transistors are solid-state components with no moving parts or wound windings, making them cheaper to manufacture while providing reliable transistor blocking through their inherent switching characteristics
Solution Approach 2:
The invention extracts the essential function of voltage symmetrization from the transformer and implements it through a simplified circuit using complementary MOS transistors. The transformer is completely removed from the design, and its blocking function is achieved through the push-pull configuration of the NMOS and PMOS transistors working in conjunction
3Reliability
If a control circuit with low impedance to ground is used, then re-conduction and oscillation are prevented, but the circuit complexity increases
Solution Approach 1:
The invention merges the functions of providing low impedance to ground and controlling the high-voltage transistor switching into a single integrated push-pull circuit. The first NMOS control transistor provides the low impedance path to ground when active, while the second PMOS control transistor provides the complementary action, eliminating the need for separate protection circuits
Solution Approach 2:
The push-pull configuration is self-regulating: when the first NMOS control transistor turns on, it automatically provides the low impedance path to ground needed to prevent re-conduction and oscillation. The circuit uses its own switching action to maintain stability without requiring external intervention or additional 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
The solution provides a control device with propagation times of 15-20ns, effectively managing high voltage transistor switching with low impedance, ensuring rapid operation and preventing re-conduction or oscillation, even at low battery voltages, while maintaining efficiency across a wide frequency range.
Implementation Method 1
a second control PMOS transistor connected between a supply terminal and the output terminal and whose gate is connected to said input terminal via a transistor bipolar arranged in a common base assembly and current-controlled on its emitter by a capacitive link circuit
Implementation Method 2
a first low internal impedance NMOS control transistor connected between ground and the output terminal and whose gate is connected to said input terminal
Data Source
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AI summary
The invention relates to a control device comprising: an input terminal (IN) for receiving a logic control signal; an output terminal (OUT) for delivering an output control signal from the high-voltage MOS transistor; a first NMOS control transistor (Q6) with low internal impedance, which is connected between the earth and the output terminal and the gate of which is connected to the input terminal; and a second PMOS control transistor (Q5) which is connected between a supply terminal and the output terminal and the gate of which is connected to the input terminal by means of a bipolar transistor (Q2) which is mounted to a common base and which is current controlled at the emitter thereof by means of a capacitive connecting circuit (C2, R2, Q1).