With an ever increasing demand for high-definition video and audio, and an explosion in high-def signals, High-Definition Multimedia Interface (HDMI) has become the de-facto standard in HDTV. HDMI is an interface that provides a high-speed link between audio/ video source devices such as notebooks, Blu-ray players and sink devices such as HDTVs for transmitting uncompressed digital audio/video signals.
The demand for low-cost highly integrated HDMI solutions is increasing, leading to the increase in number of HDMI chipsets fabricated in CMOS processes. As the chip geometries have been reduced, so has the geometric span, making them susceptible to smaller ESD events, which may lead to system failures.
ESD threats can come from any charged entity such as user’s direct touch or from hot plugging a charged cable. The internal on-chip ESD protection mostly provides an immunity of up to +/- 2KV which is not sufficient to keep the sensitive HDMI chip from becoming damaged. Effective measures must be taken to diminish the impact of such transients in order to protect the HDMI chip and prevent any data corruption between field input and device output.
Signal integrity and electrical performance are critical for maintaining the quality of HDMI’s GHz signals. Placing ESD protection on HDMI signals affects the edge rates of high-speed signals and trace impedances localized to the area of the ESD protection for single-ended and differential signals. Placing ESD components on high-speed signals is analogous to placing small capacitors on the signal lines and introducing parasitic capacitance. In order to minimize their impact on high-speed signals, it is advisable to have ESD components, for HDMI, with parasitic capacitance below 1 pF.
In addition to the electrical characteristics requirement, to ensure maximum reliability for the HDMI IC, the protection device should provide repeatable ESD immunity to and beyond level 4, IEC 61000-4-2 ESD to each of the exposed signal pins. In other words, when testing the I/O or power pin of the HDMI connector, each pin should have a minimum of ±8kV contact ESD and ±15kV air ESD handling capability.
In conjunction with ESD voltage protection level, another important parameter to consider is ESD clamping voltage. With the increasing sensitivity to overvoltage stress in today’s ICs, lowering the ESD clamping voltage will reduce the risk of being damaged further. Thus, it is important that the chosen protection device offers the lowest ESD clamping voltage possible.