A pulse generator circuit may include a diode configured to operate as an opening switch, a tank circuit in series with the diode having an admittance that is switchable from a first value to a second value that is different from the first value, and a switching system configured to cause the tank circuit to switch between the first value and the second value. The diode may saturate in less than 100 nanoseconds. A saturable core transformer may operate as a switch that controls the opening of the diode. The pulse generator may generate a plurality of pulses, each having a length of no more than 3 nanoseconds and an amplitude of at least 1 kilovolt. Electrodes may be connected to the pulse generator to deliver the plurality of pulses to biological cells.