Should FPGAS abandon the pass-gate?

Pass-transistors have been the key building block for field-programmable gate array (FPGA) circuitry for many years due to the very small switch they enable. However, passtransistor performance and reliability have been degrading with technology scaling. Transmission gates are an alternative to pass-transistors; while larger, they are more robust. We develop a new FPGA circuit optimization flow and use it to investigate the area, delay and power impact of building FPGAs out of transmission gates instead of pass-transistors in a 22nm process. Our results show that transmission gate FPGAs are 15% larger than pass-transistor FPGAs but are 10-25% faster depending on the allowable level of “gate boosting”. Without gate boosting, transmission gate FPGAs are the better option with 14% lower area-delay product. If 200mV of gate boosting is possible however, pass-transistor FPGAs remain the slightly better choice with a 2% better area-delay product. We also show that transmission gates with a separate power supply for their gate terminal enable a low-voltage FPGA with 50% less power and good delay.