Patent ID: 8724683

Claim:
A communication testing circuit comprising: a transmitting unit including a spread spectrum clock generator that generates a modulated clock signal by modulating a reference clock signal, a pseudo-random binary sequence generator that generates a pseudo-random pattern, and a signal generator that generates a transmission signal by modulating the pseudo-random pattern based on the modulated clock signal; a receiving unit including a clock and data recovery circuit that receives the transmission signal and recovers the pseudo-random pattern from the transmission signal, and a detector that compares the recovered pseudo-random pattern with a preset pseudo-random pattern and outputs a signal indicating error information; and a control unit that counts a number of errors from the signal indicating error information input from the receiving unit and decides a timing margin based on a counting result, wherein the control unit generates a modulation factor setting signal for controlling a modulation factor of the reference clock signal and a modulation frequency setting signal for controlling a modulation frequency of the reference clock signal, and outputs the modulation factor setting signal and the modulation frequency setting signal to the spread spectrum clock generator.