Minimum degradation of high-speed line’s signal integrity (SI) is an important criterion when selecting the ESD protection diode for USB2.0 connected devices. This application note provides a quick introduction to the ‘eye-diagram’ test which is the method of choice for many USB system designers to assess the suitability of an ESD diode. Procedure for the ‘eye-diagram’ test and the measurement results are then presented to demonstrate that the Diodes low-capacitance ESD diode D1213A has extremely low impact on the high speed data signals.