A high-speed variation-tolerant interconnect technique for sub-threshold circuits using capacitive boosting

This paper describes an interconnect technique for subthreshold circuits to improve global wire delay and reduce the delay variation due to process-voltage-temperature (PVT) fluctuations. By internally boosting the gate voltage of the driver transistors, operating region is shifted from subthreshold region to super-threshold region enhancing performance and improving tolerance to PVT variations. Simulations of a clock distribution network using the proposed driver shows a 66%76% reduction in $3\sigma$ clock skew value and 84%88% reduction in clock tree delay compared to using conventional drivers. A 0.4-V test chip has been fabricated in a 0.18-$\mu$m 6-metal CMOS process to demonstrate the effectiveness of the proposed scheme. Measurement results show 2.6 $\times$ faster switching speed and 2.4$\times$ less delay sensitivity under temperature variations.