The development of HDTVs and displays has accelerated the signal transmission rate. In addition, the application of high-speed serial protocols such as USB 2.0 and USB 3.0 has led to an increase in signal rates. With the increase of signal rate, the traditional ESD protection technology has become obsolete. The multi-layer varistor, the high capacitance of the silicon diode, the leakage current and the clamping voltage can not provide accurate and reliable protection to ensure that the high-speed signal does not appear obvious. The signal is degraded.
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By adopting gap technology, especially using air as a gap, considerable performance improvements have been achieved in terms of low capacitance suppressors, lower leakage currents, lower clamping voltages, and the like. In summary, after repeated or continuous ESD events, the polymer gap suppressor will degrade, while the air gap device will still maintain very low capacitance, leakage current and trigger voltage, even after 1000 ESD events in the 1s event interval. , can also maintain good performance.
Overview of Electrostatic Discharge Protection Solutions For applications with data rates of 350 Mb/s or less, 350 Ω and multi-layer varistors are an excellent choice for protection. These applications include standard-definition LCD displays, TFT displays, and most computer peripheral interfaces and connections. These signals inherently allow for high insertion loss, high clamping voltage, and trigger voltage. Since there is no signal on the power supply pin, high speed suppression is not necessary. Transient suppression diodes and multi-layer varistors can also effectively protect interface power pins like USB 2.0 and other higher speeds. However, for data communication lines such as DVI, HDMI, USB 3.0, and the latest IEEE 1394 A and B standards, high-speed rejection response to achieve minimum signal distortion is critical to system performance and circuit protection. These applications include digital video equipment, MP3 players, cell phones, PDAs, network switches, cable and satellite TV set-top boxes, printers, scanners, copiers, and computer equipment such as laptops and netbooks.
Figure 1 Electrostatic discharge suppression technology corresponding to different data rates
Suppressor Technology Comparison Table 1 gives a comparison of the advantages and disadvantages of several core techniques commonly used in electrostatic discharge suppression devices. Polymer ESD suppression devices offer the lowest leakage current in a variety of technologies and can withstand very high ESD voltage pulses, but the device will begin to degrade after multiple ESD events. In addition, the relatively high trigger voltage and clamping voltage of this type of device (50 to 100 times higher than air gap discharge products) means that more ESD pulse energy can pass through the protected circuit.
Table 1 Comparison of several different suppressor technologies
Multi-layer varistors have been widely used in a variety of electrical equipment for many years to provide effective electrostatic discharge suppression. The relatively low breakdown voltage and trigger voltage of a multilayer varistor and the ability to withstand multiple pulses are quite satisfactory. However, multi-layer varistors have high leakage current and capacitance, and reducing the harmful effects of capacitors makes them incapable of high-speed data applications.
Silicon-based transient voltage suppression devices operate in the breakdown state of standard P/N junctions, providing relatively low trigger voltages and clamping voltages compared to polymer-gap based devices. This type of device has a leakage current 10 to 20 times higher than that of an air-gap device, and its relatively high inherent capacitance results in high signal distortion and insertion loss. Air gap based devices provide the lowest capacitance and clamping voltage in all of the techniques discussed above, which operate in an inert gas breakdown state between the two electrodes. Air gap-based devices can prevent pulses up to 15kV, and their performance characteristics are quite stable after 1000 pulse shocks (see Figure 2). Air gap based device leakage current is slightly higher than polymer-gap based devices, but its capacitance and insertion loss are comparable or slightly better than polymer devices, and its clamping voltage and trigger voltage are much lower.
Figure 2 Air-gap-based devices are quite stable after 1000 pulse shocks.
Applications and End Products Many high-speed data applications and end products use hybrid protection with gap-based devices on the data and clock lines, and multi-layer varistors or silicon-based transient voltage suppression diodes in the power connection. For example, the D+ and D- lines of the USB interface require high speed protection, which can be used with discrete chips using additional multilayer varistors or transient voltage suppression devices for VDD power protection. Multiple USB interface connections are often required in PCs, laptops, netbooks and other products.
For these devices, the data line pairs of the two separate ports can be protected by a single-chip array between the USB controller and the port (as shown in Figure 3). Ideally, the ESD suppression device should be physically as close as possible to the USB port to ensure proper circuit protection.
Figure 3 Data line pairs of two separate ports can be protected by a single-chip array between the USB controller and the port.
Now, in HDTVs and monitors, HDMI connections are already very common. These connectors have a total of 19 pins, including: 3 data channel pairs (each with one ground), one TMDS pair (plus ground), DDC data, clock, CE remote lines, all of these All need high speed protection. By using one array for two data channel pairs and one array for the other data channel pair and TMDS clock pair, only two ESD suppression arrays are needed to provide effective protection for eight high-speed connections. The remaining three (DDC data, clock, CE remote line) can be protected by a discrete electrostatic discharge suppression chip.
The protection of small memory cards commonly used in digital cameras, mobile phones, and PDAs is relatively simple. The only difference is that the size of the device is small, and devices such as 0402 size can meet the requirements.
Although the 0201 size device is not sure when it will be available, it is foreseeable that 0201 size devices will appear in the future. For these SIM cards, separate high-speed suppression chips are used to protect the I/O, clock, and reset pins, while the VCC power pins use multi-layer varistors or transient suppression devices for protection.
The faster data communication speeds brought by USB, HDMI, DVI and other high-speed interfaces make traditional ESD solutions no longer effective. Multi-layer varistors and silicon-based transient voltage suppression devices have too high a capacitance, resulting in no distortion and insertion loss in high-speed data communication. New gap-based devices reduce the effective capacitance to 0.05 pF or less. In addition, gap-based devices provide very low leakage current and high stability, and can even withstand thousands of ESD events. Recent technological breakthroughs have made air gap-based ESD suppression devices with lower capacitance and lower trigger voltage than polymer devices, as well as clamp voltages. Low trigger voltage and low clamping voltage mean more accurate protection and less energy from ESD to reach sensitive devices for longer reliability.
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