## 3 HESD Structure Design for ERT
### The Second Layer SS2: Between L1-L4 and Electrodes
#### 3.3.2 The Second Stage (SS-2): One-to-Four Connection of Electrodes and Lines  
The improved HESD will work for any layer tests. To implement this task, the electrode can choose any line to connect with. The HESD is realized through adding switches in Series J and Series A (Figure 7). \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c c c c} \hline \hline
**Layer n** & & & & **First Test** & & & & **Second Test** & & & & & **Third Test** & & & & & **Fourth Test** & \\ \hline \multirow{2}{*}{layer 1} & electrode & E1 & E2 & E3 & E4 & E2 & E3 & E4 & E5 & E3 & E4 & E5 & E6 & E4 & E5 & E6 & E7 \\  & Line & L1 & L2 & L3 & L4 & L2 & L3 & L4 & L1 & L3 & L4 & L1 & L2 & L4 & L1 & L2 & L3 \\ \hline \multirow{2}{*}{layer 2} & Electrode & E1 & E3 & E5 & E7 & E2 & E4 & E6 & E8 & E3 & E5 & E7 & E9 & E4 & E6 & E8 & E10 \\  & Line & L1 & L3 & L1 & L3 & L2 & L4 & L2 & L4 & L3 & L1 & L3 & L1 & L4 & L2 & L4 & L2 \\ \hline \multirow{2}{*}{layer 3} & electrode & E1 & E4 & E7 & E10 & E2 & E5 & E8 & E11 & E3 & E6 & E9 & E12 & E4 & E7 & E10 & E14 \\  & Line & L1 & L4 & L3 & L2 & L2 & L1 & L4 & L3 & L3 & L2 & L1 & L4 & L4 & L3 & L2 & L1 \\ \hline \multirow{2}{*}{layer 4} & electrode & E1 & E5 & E9 & E13 & E2 & E6 & E10 & E14 & E3 & E7 & E11 & E15 & E4 & E8 & E12 & E16 \\  & Line & L1 & L1 & L1 & L1 & L2 & L2 & L2 & L2 & L3 & L3 & L3 & L3 & L4 & L4 & L4 & L4 \\ \hline \multirow{2}{*}{layer 5} & electrode & E1 & E6 & E11 & E16 & E2 & E7 & E12 & E17 & E3 & E8 & E13 & E18 & E4 & E9 & E14 & E19 \\  & Line & L1 & L2 & L3 & L4 & L2 & L3 & L4 & L1 & L3 & L4 & L1 & L2 & L4 & L1 & L2 & L3 \\ \hline \multirow{2}{*}{layer 6} & electrode & E1 & E7 & E13 & E19 & E2 & E8 & E14 & E20 & E3 & E9 & E15 & E21 & E4 & E10 & E16 & E22 \\  & Line & L1 & L3 & L1 & L3 & L2 & L4 & L2 & L4 & L3 & L1 & L3 & L1 & L3 & L1 & L4 & L2 & L4 & L2 \\ \hline \multirow{2}{*}{layer 7} & electrode & E1 & E8 & E15 & E22 & E2 & E9 & E16 & E23 & E3 & E10 & E17 & E24 & E4 & E11 & E18 & E25 \\  & Line & L1 & L4 & L3 & L2 & L2 & L1 & L4 & L3 & L3 & L2 & L1 & L4 & L4 & L3 & L2 & L1 \\ \hline \multirow{2}{*}{layer 8} & electrode & E1 & E9 & E17 & E25 & E2 & E10 & E18 & E26 & E3 & E11 & E19 & E27 & E4 & E12 & E20 & E28 \\  & Line & L1 & L1 & L1 & L1 & L1 & L2 & L2 & L2 & L2 & L3 & L3 & L3 & L3 & L4 & L4 & L4 & L4 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Testing electrodes and the corresponding lines. Figure 7: Topology structure of ESD for implementing all layer tests. Series J is a series of switches designed to solve the problem of L113L113. In Section 3.3.1, the problem in the first and the third test of layer two is the so-called L1L3 problem. Every four electrodes are added to four Series J switches. E1-E4 add J1-J4, in which J1 makes E3 connected to L1, and J2-J4 makes E1 connected to L2-L4. With these improvements, the L1L3 problem is solved by switching one pair of L1L3 to L2L4, so four testing electrodes will be connected to four lines of L1-L4, respectively. In this pattern, realization for the first test in the second layer is: E1-J2-L2, E3-J1-L1, E5-J8-L4, and E7-D7-L3. All L1L3 problems can be solved with the same mode. Based on series J, Series A is designed to further solve the L2L4 problem and one-line problem. The L2L4 problem appears at the second test in layer 2, where four testing electrodes correspond to L2L4L2L4, which means that two electrodes are linked to the same line. The one-line problem is that four testing electrodes all match with one line. The above two problems could be settled by adding four Series A switches for four electrodes. Taking E1-E4 cell as an example, switches A1-A4 are added as shown in Figure 7. A1 links E4 to L1. A2-A4 link E2-E4 to E1, and D1 through to J2-J4 connect to any line of L1-L4. When the L2L4 problem happens, one pair of electrodes corresponding to L2L4 is adapted to L1L3 via Series A and Series J switches. A L2L4 problem for the second test in layer 4 is solved as: E2-A2-D1-L1, E6-D6-L2, E10-A10-J11-L3, and E14-A14-J16-L4. When a one-line problem appears, a similar mode is fixed.