Signal conversion device and motor drive system

The invention provides a signal conversion device and a motor drive system. The signal conversion device of one embodiment of the invention includes a first signal input terminal, a second signal input terminal, and a detector. A first AC signal is supplied to the first signal input terminal from a signal source. The second signal input terminal is supplied with an in-phase signal that is in phasewith the first AC signal and an opposite-phase signal that is opposite in phase with the first AC signal. The second signal input terminal is supplied with a second AC signal whose phase has been switched by a switchover between the in-phase signal and the opposite-phase signal from the signal source. The detector detects, using the supplied first AC signal, whether the supplied second AC signalis the in-phase signal or the opposite-phase signal. 本发明提供信号转换装置和马达驱动系统。本发明的一个方式的信号转换装置具有：第1信号输入端子，其从信号源被提供第1交流信号；第2信号输入端子，其从所述信号源被提供第2交流信号，该第2交流信号包括与所述第1交流信号为同相的同相信号和与所述第1交流信号为反相的反相信号，并且相位根据所述同相信号和所述反相信号的切换而切换；以及检测部，其使用所述提供的第