It must: limit the voltage to a maximum of 1.5 V, have symmetrical limiting, be capable of accepting a current of 2 A, and leak less than 100 µA at 1 V. Two Zener diodes ... in the circuit output is ...

The PCI clamp diode limitsthe voltage to a level that doesn’t harmthe input ... 2). The circuit from the FPGA’sapplication notes requires a change,which you can accomplish without redesigningthe PCB ...