An energy-efficient near/sub-threshold FPGA interconnect architecture using dynamic voltage scaling and power-gating

The rapid development of the Internet-of-Things requires hardware that is both low-energy and flexible, and a near/sub-threshold FPGA is a very promising solution. In the design of near/sub-threshold FPGAs, the biggest challenge is reducing global interconnect energy, which is the most energy-consuming part in the entire FPGA. Dynamic voltage scaling is an effective technique in reducing energy, but it is not widely used in FPGA interconnects because of the high area overhead of separately provisioning the buffers in the switch boxes to support different voltages on different paths. A low-swing interconnect, which removes buffers, allows this technique to be applied to the FPGA interconnects. In this paper, we propose a novel low-swing FPGA interconnect architecture that integrates dynamic voltage scaling and power-gating techniques with custom tool support. While the power-gating technique is widely used in existing designs for reducing leakage energy of idle drivers and buffers, we also apply power-gating to configuration bitcells in switch boxes, because it is a dominant energy consumer in near/sub-threshold. Including the energy overhead of voltage regulators, our work achieves a 10.1% energy saving in active circuits, 27.0% - 91.3% in idle circuits, and 19.0% - 53.1% in the entire FPGA on average, compared to an already optimized base case that only uses low-swing interconnect but no dynamic voltage scaling or power-gating. In addition, our dynamic voltage scaling allows us to adjust the delay of the low-swing FPGA interconnect from 0.14μs to 0.43μs or adjust its energy per operation from 5.5pJ to 35.7pJ when implementing the MCNC benchmarks at 0.6V.