Nanosecond pulse generator, using fast recovery diodes for cell electromanipulation

Design and operation of a fast recovery diode based pulse generator is presented. The generator produces 3.5-ns-wide, 1200 V amplitude unipolar pulses or +/- 600-V bipolar pulses into 50-Omega load at the maximum repetition rate of 100 kHz. Pulses shorter than 10 ns are essential for the studies of biological cell response to high electric fields while avoiding ordinary electroporation effects dominant at long pulses. Bipolar pulses are used for the studies of biological cell response to high electric fields when the net transfer of charge is undesirable. The bipolar pulse is produced from a unipolar pulse with the help of a shorted transmission line. This transmission line delays and inverts the initial pulse, so the output is the sum of the initial and the inverted and delayed pulses. The use of mass-produced fast recovery surface-mount rectifier diodes in this circuit substantially simplifies the generator and results in low cost and very small footprint. Similar diode switched pulse generators have been described in the literature using mostly custom fabricated snap-recovery diodes. Here we give an example of an ordinary low-cost diode performing similarly to the custom. fabricated counterpart. The diode switched circuit relaxes the requirement on the speed of the main closing switch; in our case, a low-cost power metal-oxide semiconductor field-effect transistor (MOSFET)-saturable core transformer combination.