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AUGUST 2019 I DESIGN007 MAGAZINE 73 PDN impedance by at least 0.9 ohms for fre- quencies above 10 MHz. Second, the SSN plots of the power nets in the time domain for all PDN conditions are shown in Figure 3. SSN is generated by the in- teraction between PDN impedance and tran- sient current in the buffer of the transmitting (Tx) IC during signal transmission. The tran- sient current will increase when more Tx buf- fers in the IC are toggling simultaneously to transmit data signals. In PDN condition B, the amplitude of SSN in Figure 3 (iii) is double of that in Figure 3 (ii) due to larger transient cur- rent in the IC with more Tx buffers toggling. On the other hand, when eight Tx buffers are toggling simultaneously at 1 Gbps, PDN condi- tion A with the poorest decoupling and larg- est impedance (in the hundreds of MHz) suf- fers the largest amplitude of SSN: 505 mVpp, shown in Figure 3 (i). On the contrary, PDN condition D with the best decoupling (13 0.22- uF capacitors) and the smallest impedance experience the smallest amplitude of SSN— 95mVpp, shown in Figure 3(v) —which fulfils Figure 3: Simulated SSN plots for PDN conditions listed in Table 1.