A signal generator adapted for delivery of tissue ablation energy comprising: a therapy output block including a voltage conversion circuit, an energy storage circuit and an output control circuit; an input/output circuit adapted to couple to a probe for delivery of tissue ablation energy, the input/output circuit defining a plurality of output channels such that a probe coupled thereto and having a plurality of electrodes can be used with separate activation of subsets of the plurality of electrodes; a user interface allowing a user to control the signal generator and adapted to display one or more parameters of tissue ablation energy to be delivered by the signal generator; a controller coupled to the therapy output block and the user interface; a memory coupled to the controller and having stored instructions for the delivery of a treatment cycle, characterized in that the treatment cycle comprises: a first output of a first polarity at a first amplitude and having a first pulse width as a first phase; a second output of a second polarity, opposite the first polarity, at a second amplitude and having a second pulse width, the second pulse width being less than half the first pulse width; and a third output using the second polarity at a third amplitude less than the second amplitude, the third pulse width being greater than the second pulse width; wherein the sum of the first, second and third outputs yields a balanced charge to limit muscle stimulation associated with the multiphasic ablation waveform; wherein the stored instructions define the first and second amplitudes to exceed an irreversible electroporation threshold, and the third amplitude to be less than an irreversible electroporation threshold. a therapy output block including a voltage conversion circuit, an energy storage circuit and an output control circuit; an input/output circuit adapted to couple to a probe for delivery of tissue ablation energy, the input/output circuit defining a plurality of output channels such that a probe coupled thereto and having a plurality of electrodes can be used with separate activation of subsets of the plurality of electrodes; a user interface allowing a user to control the signal generator and adapted to display one or more parameters of tissue ablation energy to be delivered by the signal generator; a controller coupled to the therapy output block and the user interface; a memory coupled to the controller and having stored instructions for the delivery of a treatment cycle, characterized in that the treatment cycle comprises: a first output of a first polarity at a first amplitude and having a first pulse width as a first phase; a second output of a second polarity, opposite the first polarity, at a second amplitude and having a second pulse width, the second pulse width being less than half the first pulse width; and a third output using the second polarity at a third amplitude less than the second amplitude, the third pulse width being greater than the second pulse width; a first output of a first polarity at a first amplitude and having a first pulse width as a first phase; a second output of a second polarity, opposite the first polarity, at a second amplitude and having a second pulse width, the second pulse width being less than half the first pulse width; and a third output using the second polarity at a third amplitude less than the second amplitude, the third pulse width being greater than the second pulse width; wherein the sum of the first, second and third outputs yields a balanced charge to limit muscle stimulation associated with the multiphasic ablation waveform; wherein the stored instructions define the first and second amplitudes to exceed an irreversible electroporation threshold, and the third amplitude to be less than an irreversible electroporation threshold.