对 HDMI-SDI/SDI-HDM I转换器的全面保护
08 December 2022 / by Anindita Bhattacharya
无论您是在体育场的巨型屏幕上观看棒球比赛的动作回放、在大屏幕电视上观看电影，还是在笔记本电脑上播放视频，都期望获得高质量的视听 (AV) 体验。超高清串行数字接口 (UHD-SDI) 和高清多媒体接口 (HDMI) 是数字 AV 传输的两个标准。UHD-SDI 对通过同轴电缆或光纤传输未压缩和未加密的数字 AV 信号加以标准化。HDMI 是一种数字接口，用于将高清、高速数字多轨音频和未压缩视频信号从 HDMI 兼容源传输到视听显示器。尽管二者都可以将超高清 AV 信号从信号源传输到显示器，但 HDMI 更适合连接电脑、游戏机、蓝光/DVD 播放器、电视、投影仪等消费电子产品。 UHD-SDI 是专业室内/室外视频制作和电视广播等高端应用的首选，因为它支持远距离传输，并借助电缆两端的物理锁定机制实现可靠连接。UHD-SDI 同轴电缆可以将信号传输远达 300 英尺，而 HDMI 电缆即使在 50 英尺以内也会出现信号过渡衰减的问题。这两种接口可以通过 HDMI-SDI 或 SDI-HDMI 转换器一起使用。例如，如图 1 所示，HDMI 显示器用于 SDI 流的置信度监控，从而无需使用经过专门校准的 SDI 专用显示器。
Figure 1. HDMI-SDI converter
Protection of Ports and Interfaces
An HDMI-SDI/SDI-HDMI converter box uses a DC power jack with an input voltage of 12V to power up the circuit. Abnormal power situations such as inrush current, overvoltage, short-circuit, electrical transients, and steady-state fault conditions are not uncommon in such a power line. An eFuse precisely detects those electrical surges and provides robust security to the downstream load by gracefully disconnecting it from the power source during those anomalous situations.
The other two ports besides the DC power jack of an HDMI-SDI/SDI-HDMI converter are HDMI and SDI ports. Protecting the converter's interfaces from electrostatic discharges (ESD) is imperative. We plug and unplug the ports from the converter several times, and when we touch or engage with the ports, it is possible to generate electrostatic discharge. These ESD events can be generated from a user (human body) or the stored charge on a cable. The electrostatic spike can reach up to tens of thousands of volts – easily damaging the converter's sensitive electronic circuit. Hence, ESD protection for each interface is not just important; it is essential. Semtech provides the complete protection of an HDMI-SDI/SDI-HDMI converter, as shown in the block diagram in figure 2.
Figure 2. Protection of HDMI-SDI converter (Top) and SDI-HDMI converter (Bottom)
Let us look into how to shield an HDMI-SDI/SDI-HDMI converter from electrical transients, electrical overstress (EOS) and ESD events.
DC Power Line Protection
An HDMI-SDI converter box receives 12V via an adapter from a wall outlet to power up the circuit. Some modern-day converters also use a USB Type-C connector for powering the circuit. Either of these applications needs a shield against inrush current, overvoltage, under voltage, short circuit, and over-temperature faults. Semtech's HotSwitch® devices are eFuses with a low-resistance integrated MOSFET connected in series to the power rail that protects electronics systems against typical electrical transients and fault conditions. HotSwitch HS2950P is an excellent system protection solution for HDMI-SDI converters to limit currents and voltages to safe levels during fault conditions. HS2950P, shown in Figure 3, is a single-channel integrated eFuse with a wide input voltage range from 2.7V to 29V, supporting up to 5A output current and a low 25mΩ (typical) Rds(on). Bundled in a tiny 3x3mm 12-pin DFN package, HS2950P utilizes flexible and programmable protection features to handle multiple fault conditions. Programmable features include
Precise overvoltage protection
A soft start to protect against inrush currents for various load requirements.
Figure 3. Application diagram of HS2950P at 12V power line
After protecting the power line from fault conditions, we also need to consider how to protect it from ESD/EOS events. The DC power line requires an ESD protection device with more than the supply voltage, fast response time and low clamping voltage. Semtech's SurgeSwitch™ TDS2211P device is ideally suited to safeguard the DC power line of an HDMI-SDI/SDI-HDMI converter. TDS2211P, shown in Figure 3, does not use a conventional PN junction TVS diode for protection. Instead, it uses a surge-rated FET as the primary protection element, which is used as a voltage-controlled switch. Check this video to learn about the advantages of a SurgeSwitch in detail. TDS2211P has an operating voltage of 22V. It offers a minimum breakdown voltage of 25V and a peak pulse current of 40A (tp=8/20µs). TDS2211P provides transient protection as per the specification in IEC 61000-4-2 (ESD) at ±30kV (Air) and ±30kV (Contact). This part is available in a DFN package with a 1.6 x 1.6 x 0.55 mm nominal dimension.
Protection of the HDMI Port
A standard Type A HDMI connector contains 19 pins, including four high-speed transition minimized differential signal (TMDS) pairs and six non-high-speed channels (+5V power, HPD, CEC, SDA, SCL, HEC) to fulfill the digital data transition. The TMDS algorithm transmits the video and audio signals from the transmitter to the receiver using three TMDS data channels and one TMDS clock channel. In the HDMI 2.0 specification, these three channels carry differential data signals of 18Gbps, with each channel at 6Gbps. Check this video to learn more about HDMI protection.
Semtech's RClamp®0594P (Figure 4) is highly capable of protecting the high-speed differential lines and the six other non-high-speed lines of HDMI 2.0 interfaces. It protects the high-speed data lines with a typical junction capacitance of only 0.3pF. RClamp0594P has an operating voltage of 5V with a minimum breakdown voltage of 6V. It has a dynamic resistance of 0.19Ω (Typical). RClamp0594P provides transient protection as per the specification in IEC 61000-4-2 (ESD) at ±17kV (Air) and ±12kV (Contact). The flow-through package design simplifies the PCB layout and maintains the undamaged signal integrity. RClamp0594P is available in a 10-lead DFN package with a nominal dimension of 2.5 x 1.0 x 0.55 mm.
Figure 4. ESD protection of the HDMI port
Protection of the UHD-SDI Port
The 12G UHD-SDI standard transmits and receives video and embedded audio at a nominal rate of 11.88 Gbps. The standard is primarily used for 4k/UHDTV-1 (2160p) video formats. Extremely low capacitance is one of the main requirements of the needed ESD protection device for a UHD-SDI interface. The other requirement is to provide enough surge protection for the interface, as it is often used in harsh outdoor environments.
Semtech's RClamp1011ZC features superior ESD protection characteristics and is specifically designed to protect the UHD-SDI interface with BNC ports, as shown in Figure 5. It protects one bidirectional high-speed data line operating at 1.0V. It offers superb ESD protection while maintaining an exceptionally low typical line-to-line capacitance of 0.17pF, ensuring signal integrity. It also features a typical dynamic resistance of only 0.32Ω. RClamp1011ZC has a high ESD withstand voltage of ±10kV contact per IEC 61000-4-2. This device is also great for EOS protection due to its high peak pulse current capability (2.5A, tp=8/20µs). RClamp1011ZC is available in a compact 0201 DFN package (0.6x 0.3 x 0.25 mm).
Figure 5. ESD protection of the UHD-SDI port
HDMI and UHD-SDI are two prominent AV standards. An HDMI-SDI or SDI-HDMI converter allows one to interconnect different AV equipment without any issues. The popularity of these converters is on the rise. With massive improvements in data transmission speed, video quality and resolution, the converters are more exposed to electrical transients, steady-state faults, ESD, and EOS threats. These faults can easily damage the high-end device connected to the HDMI-SDI or SDI-HDMI interface. Semtech's wide range of dependable protection products can shield any HDMI-SDI/SDI-HDMI converter from any abnormal condition. Its highly efficient HotSwitch, SurgeSwitch, and TVS diode products protect all ports and interfaces of an HDMI-SDI/SDI-HDMI converter. Consumers can experience a problem-free, fault-free connection to any HDMI-SDI/SDI-HDMI converter by shielding its ports and interfaces with Semtech protection products.
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Semtech, the Semtech logo, HotSwitch, and RClamp are registered trademarks or service marks, and SurgeSwitch is a trademark or service mark, of Semtech Corporation or its subsidiaries.