In the past, high-definition digital content could only be carried on a physical disk, and could only be played on a dedicated device; nowadays, broadband connections are everywhere, and high-definition digital content can be transmitted and customized in the form of "streaming" from the "cloud" to computers, smart On a mobile phone or any other connected device. Traditional TV is an independent terminal that can only receive broadcast and TV programs. Because it does not have the networking function we are used to, it will eventually become an outdated product. Therefore, the smart TV industry came into being.
Smart TV refers to a TV that integrates Internet functions, which can provide more advanced computing power and networking functions than today's ordinary TVs. In order to obtain higher performance, smart TVs usually use the latest generation of technology. As smaller and more advanced integrated circuits continue to promote the development of TV sets, new challenges will appear in the field of electromagnetic compatibility (EMC), because these high-speed signal interfaces will be threatened by static electricity and cable discharge events under normal use conditions.
This article will provide protection solutions for the two most common and sensitive interfaces on smart TVs: HDMI and Gigabit Ethernet interfaces.
ESD/CDE protection of HDMI
Since its introduction, HDMI (High Definition Multimedia Interface) has gradually gained popularity. This interface is widely used in the field of consumer electronics for the transmission of high-definition digital content. However, as a high-performance interface, HDMI is extremely sensitive to cable discharge from hot plugs and direct electrostatic discharge (ESD) from users.
To ensure its normal function, HDMI-based systems must protect all possible exposed interface signals and power pins to meet or exceed the EOS of IEC 61000-4-2, Level 4 (±15kV air discharge, ±8kV contact discharge) (Excessive electrical stress) standard requirements without damage. The HDMI chip currently works at 2.25Gbps and will soon reach 3.4Gbps. At such a high data transmission rate, attention to signal integrity and impedance requirements will far exceed the HDMI Conformance Test Specification (CTS). The specification requires that all HDMI receiving devices must maintain the differential impedance of the high-speed line at 100Ω±15%.
Under the data transmission rate of 3.4Gbps, how to provide low clamping voltage protection without adding additional capacitive load is very critical. In order to effectively suppress the impact of transient surges on the low clamping voltage, more silicon area is required in the TVS diode. But increasing the silicon area will come at the expense of increased capacitance. This dilemma can be solved by constructing a small-capacitance diode array around the TVS diode that handles the surge. This method can effectively reduce the total capacitance of the protection circuit while maintaining a strong surge protection capability. Semtech has pioneered advanced integrated TVS devices using this architecture, which can obtain good protection without the cost of high capacitance.
RClamp0584J is a best example of this kind of integrated TVS protection device (Figure 1). This device is the latest member of the RailClamp series of high-speed interface protection products. The performance of this four-wire, 5V working voltage protection device exceeds the IEC 6100-4-2 level 4 protection requirements for electrostatic transients. Figure 1 also clearly shows that this device uses a unique package design. The term "Flow through" package comes from Suntech. This package allows traces to pass directly through the protection device, thus minimizing additional parasitics caused by the interruption or mismatch of the balanced differential pair Inductance and capacitance.
When adding ESD protection to the HDMI interface, it must be ensured that the device has the least impact on signal integrity. The eye pattern test can show any signal distortion on the source interface. The eye pattern can use a bit pattern that surrounds the HDMI eye mask to form an "open" eye. This clean eye pattern can verify good signal integrity. Figure 2 shows an example of an eye diagram test. As a reference, the picture on the left is the HDMI video signal without any protection, and the picture on the right is the HDMI interface signal with TVS protection devices added.
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