Abstract: An error detection circuit, applied to a digital communication system with embedded clock, includes a time delay unit, a clock embedding encoding unit, a comparing unit and a packet error counting unit. The time delay unit delays a first digital encoded signal for a period of time. The clock embedding encoding unit generates a second digital encoded signal according to a first digital decoded signal, wherein the first digital decoded signal is generated by decoding the first digital encoded signal. The comparing unit is coupled to the time delay unit and the clock embedding encoding unit respectively and compares the first digital encoded signal with the second digital encoded signal to generate a compared result. The packet error counting unit is coupled to the comparing unit and counts a packet error rate according to the compared result and then provides a flag according to the packet error rate.