Coaxial Pulse Generator Circuit for Flat-Top Electroporation Pulses
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Solution Overview
Problem
Existing electrosurgical generators face challenges in generating high-voltage pulses with ultrashort durations and steep rise/fall times suitable for electroporation of biological cells, as traditional methods often result in pulse shapes with ringing and limited amplitude.
Innovation Solution
A pulse generating circuit utilizing an open circuit coaxial transmission line in conjunction with a series-connected avalanche transistor switching element, where the impedance of the transmission line matches the impedance of the transistors and load, producing a 'flat-top' pulse with controlled duration and amplitude, achieving pulses with rise and fall times less than 2 ns and amplitudes of 500 V or more.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If traditional pulse generating methods are used, then the circuit complexity is reduced, but the pulse rise time and fall time are too slow (greater than 2 ns) and ringing occurs
Solution Approach 1:
The patent divides the switching element into multiple series-connected avalanche transistors (typically 3-5 transistors in series). Each transistor handles a portion of the total voltage, enabling faster switching speeds (rise and fall times less than 2 ns) while distributing the voltage stress. This segmentation allows achievement of ultrashort pulse durations without excessive circuit complexity.
Solution Approach 2:
The patent employs a nested structure where multiple avalanche transistors are arranged in series within the switching element, and this switching element is integrated within the transmission line-based pulse generation circuit. The transistors are nested in a configuration where each transistor's collector connects to the next transistor's base, creating a cascaded structure that achieves fast switching while maintaining compact circuit implementation.
2Strength
If high voltage pulses are generated, then the amplitude is sufficient for electroporation (500 V or more), but the transistor collector-base breakdown voltage is exceeded
Solution Approach 1:
The patent segments the high voltage pulse generation across multiple series-connected avalanche transistors. If three transistors are used with a 1 kV supply voltage, each transistor experiences approximately 333 V, well below typical 600-1000 V collector-base breakdown ratings. This voltage distribution enables generation of high amplitude output pulses (500 V or more) while keeping individual transistor voltage stress within safe operating limits, ensuring reliability.
Solution Approach 2:
The patent changes the operating parameters of the avalanche transistors by operating them in the avalanche breakdown region rather than in linear amplification mode. By carefully selecting the supply voltage and transistor characteristics, the circuit generates high voltage pulses while maintaining individual transistor voltages below breakdown thresholds through proper parameter selection and matching.
3Loss of energy
If the transmission line impedance does not match the load and transistor impedance, then the circuit is simpler to design, but pulse ringing occurs and energy transfer is inefficient
Solution Approach 1:
The patent achieves impedance matching by carefully selecting and adjusting key parameters: the transmission line characteristic impedance is chosen to match the parallel combination of the transistor output impedance and load impedance. The supply voltage, transistor characteristics, and transmission line dimensions are optimized together to achieve maximum energy transfer efficiency and eliminate pulse ringing, transforming a potentially complex impedance matching problem into a systematic parameter optimization approach.
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 circuit generates ultrashort pulses with minimal ringing and high amplitude, suitable for electroporation, by matching the transmission line impedance with the transistors and load, ensuring efficient energy transfer and preventing transistor breakdown, thus enhancing the effectiveness of electrosurgical procedures.
Implementation Method 1
a plurality of series connected avalanche transistors; a trigger pulse generator configured to generate a trigger pulse to activate the plurality of series connected avalanche transistors
Implementation Method 2
an open circuit coaxial transmission line connected between the switching element and the voltage source to be charged by the voltage source when the switching element is in an OFF state and to be discharged when the switching element is in an ON state
Data Source
Figure 1~2(ii)
Figure 3A~4
Figure 5
AI summary
The present invention relates to a pulse generating circuit for an electrosurgical generator, for generating a waveform suitable for causing electroporation of biological tissue. The pulse generating circuit comprises a voltage source connectable to a load via a switching element, and an open circuit coaxial transmission line connected between the switching element and the voltage source to be charged by the voltage source when the switching element is in an OFF state and to be discharged when the switching element is in an ON state. The switching element comprises a plurality of series connected avalanche transistors, and a trigger pulse generator configured to generate a trigger pulse to activate the plurality of series connected avalanche transistors. Furthermore, the impedance of the coaxial transmission line is configured to match a sum of (i) the impedance the plurality of series connected avalanche transistors, and (ii) the impedance of the load.