Impact of ESD protection devices on circuit operation is very important in gigahertz applications. In this paper, the impact of different ESD protection methodologies on CML drivers is discussed. ESD protection is provided using MOSFET and SCR devices. Study of the interaction between driver and ESD protection circuit shows that jitter is very sensitive to parasitics of ESD protection circuits. Furthermore, an analysis shows that substrate-triggering has less impact on jitter compared to gate-coupling.