In an electronic device and a method of generating composite electrical signals, a plurality of post-processing software is installed. An output file, which comprises times and voltages of data points that represent an electrical signal, of an electronic circuit simulation software is loaded, and is read using the installed post-processing software. A time interval of outputs of the electrical signal is obtained by selecting an output type of the electrical signal. The worst bit combination of outputs of the electrical signal is analyzed according to the times, the voltage, and the time interval, and a composite electrical signal is generated according to the worst bit combination.