A power amplifier comprises first and second power transistor stages that receive first and second supply voltages, respectively. In writing in the memory cells, the drain electrodes of the memory cells are selected at a rate of one out of four drain electrodes and the voltage CDV is applied to the so selected drain electrode. Improved collection systems and techniques for the process are described so that commercial applications of sperms samples as well as the resulting animals may be achieved. When the second differential amplifier is in an operating state and the first differential amplifier is in a non-operating state, the switch is controlled to be on.