Fault Diagnosis of Via-Switch Crossbar in Non-volatile FPGA
Ryutaro Doi1,a, Xu Bai2, Toshitsugu Sakamoto2 and Masanori Hashimoto1,b
1Department of Information Systems Engineering, Osaka University, Japan
adoi.ryutaro@ist.osaka-u.ac.jp
bhasimoto@ist.osaka-u.ac.jp
2NEC Corporation, Japan
ABSTRACT
FPGA that exploits via-switches, which are a kind of non-volatile resistive RAMs, for crossbar implementation is attracting attention due to its high integration density and energy efficiency. Via-switch crossbar is responsible for the signal routing by changing on/off-states of via-switches. To verify the viaswitch crossbar functionality after manufacturing, fault testing that checks whether we can turn on/off via-switches normally is essential. This paper confirms that a general differential pair comparator successfully discriminates on/off-states of viaswitches, and clarifies fault modes of a via-switch by transistorlevel SPICE simulation that injects stuck-on/off faults to atom switch and varistor, where a via-switch consists of two atom switches and two varistors. We then propose a fault diagnosis methodology that diagnoses the fault modes of each via-switch using the comparator response difference between normal and faulty via-switches. The proposed method achieves 100% fault detection by checking the comparator responses after turning on/off the via-switch. In case that the number of faulty components in a via-switch is one, the ratio of the fault diagnosis, which exactly identifies the faulty varistor and atom switch inside the faulty via-switch, is 100%, and in case of up to two faults, the fault diagnosis ratio is 79%.
