Communication device and communication system

A communication device to be used as a master node in a communication system configured to use a pulse width modulation signal as transmission code among a plurality of nodes connected to a communication line, the communication device comprising:

• a transmission transistor configured to be connected to the communication line;
• a detector configured to detect a variation in current during an on-period of the transmission transistor;
• and
• a communication circuit configured to determine off-timing of the transmission transistor based on timing of occurrence of the variation in current, wherein
• the timing of occurrence of the variation in current corresponds to on-timing of a second transmission transistor provided in a slave node, and
• the communication circuit is configured to determine the off-timing of the transmission transistor such that a simultaneously-on period TB of the transmission transistor and the second transmission transistor fulfills TB=(2n−1)/2f, where f is a frequency of electromagnetic interference (EMI) noise and n is a natural number.