Applying TLP on HDMI Port for System Level Test

As high definition, digitalized audio, video transmission port, HDMI (High Definition Multimedia Interface) has been widely used on devices such as PC, TV, set-top box, game console and projector. With the continuous improvement of video resolution, it is necessary to use interface protocol with higher transmission rate to meet the requirement. The HDMI port protocol has been upgraded from the original 1.0 version to the widely used HDMI 2.1 currently, and its maximum transmission rate has been increased to support 48Gpbs which can support the highest resolution of 4K*2K@120Hz and 8K*4K@60Hz video transmission. 

Table 1: Information of various HDMI port versions

The HDMI port is defined as five types which include Type-A, B, C, D, and E. Except for the Type-B port which has 29 pins, the other four all have 19 pins. Among them, the most widely used is the Type-A port. As shown in Figure 1, its pin definition consists of TMDS high-speed communication channel and clock control channel, DDC/SCL/SDA auxiliary communication channel, HPD hot swap detection and VCC power supply.

Figure 1: HDMI Type-A port definition

For such high-speed and multi-channel signal transmission of the HDMI port, it is important to prevent ESD transient pulses from interfering with the normal communication of HDMI during the use of the product; and may even damage the HDMI port control chip. Therefore, it is essential to conduct ESD test for HDMI port of various products. However, when using the IEC 61000-4-2 electrostatic gun for ESD level testing, you can only get a simple Pass or Fail test result under different output voltages. In order to ensure that a reliable ESD protection circuit can be designed in early stage, and to quantify the ESD withstand voltage of each signal line of the HDMI port; TLP (Transmission Line Pulse) can be used to conduct a complete assessment test on the HDMI port signal line; and choose suitable TVS products for ESD protection by HDMI port withstand voltage value that TLP measured.

TLP is a transmission line pulse test system which can output a current square wave to simulate test which is the same level of ESD electrostatic gun. During the TLP test, test system is able to record working voltage of ESD current that enters pin under test of unit with every current square wave output. By setting current square waves with various strengths, sufficient voltage values will be measured from unit under test. The recorded IV data can be plotted in a table to get a TLP curve by which the ESD withstand voltage of unit under test or TVS clamping voltage under different ESD levels can be read clearly. This is also the main reason why various chip manufacturers use TLP to simulate ESD testing. 

By comparing different TLP curves, you can directly read the clamp voltage value of TVS products. Under the same level of output current, the lower the TVS clamping voltage, the more obvious the ESD protection effect. As shown in Figure 2 below, when the same TLP outputs 15A current, the clamping voltage of TVS_AZ176S-04F is 4V, and the clamping voltage of TVS_AZ1045-04F is 10.2V. Obviously, TVS_AZ176S-04F is better for suppressing ESD interference or damage to circuit communication.

Figure 2: TLP curves for various TVS products

Except for conducting TLP test for TVS products and I/O pins of various chips, TLP can also apply to pins of other type ports for different products;, and it can more intuitively reflect the ESD withstand voltage of the port pins. For example, continuously increase output current on TMDS high-speed signal line of HDMI port during test until failure detection of HDMI port occurs. Record I-V data and integrate it in TLP curve which is compared with TLP curve of TVS product to select the most applicable TVS product as ESD protection. 

As shown in Figure 3 below, use TLP to test the TMDS circuit of a computer HDMI port to obtain its TLP curve. When ESD energy enters the HDMI_TMDS and Clock control circuit, the maximum operating voltage is 24V and 21V. When selecting TVS, it is only necessary to ensure that the TLP clamping voltage of TVS is less than 21V which is able to protect HDMI_TMDS lines from damage of ESD。

Figure 3: TLP curve of HDMI_TMDS/CLK

According to the test results, the ESD withstand voltage of different IC chips will be vary due to change of manufacturing process. With the continuous introduction of higher chip manufacturing processes, the ESD tolerance of IC becomes weaker and the clamping voltage of TVS protection device at port end needs to be lower. For various HDMI ports, Amazing Microelectronic Corp. provides TVS solutions as shown in the table below for commonly used HDMI1.4, 2.0 and 2.1.

Reference: [1]. HDMI Official website: https://www.hdmi.org