Effective Drive Current for Near-Threshold CMOS Circuits’ Performance Evaluation: Modeling to Circuit Design Techniques

This paper presents an effective current model (I
_eff
) for a near-threshold voltage (NTV) inverter and two-input NAND/NOR gates. The proposed model is validated by 2-D technology computer-aided design mixed-mode device simulations and HSPICE simulations at two different technology nodes. When compared with our model, the existing nominal supply voltage I
_eff
models fail to estimate an inverter/NAND/NOR gate performance in the NTV regime. The proposed model is also validated for process, voltage, and temperature variations. Performance variation due to layout-dependent effects (LDEs) and inverse narrow width effect (INWE) are significant in the NTV regime. Therefore, the model is validated while considering LDEs. We show that due to LDEs and INWE, the value of I
_eff
per unit width is a function of the device width and the number of fingers. To account for this effect, a systematic methodology is presented to optimize a circuit performance in the NTV domain. An inverter chain with C
_out
/C
_in
= 2000 designed employing our methodology results in 3.2%, 35%, and 30% improvement in the delay, energy per operation, and total transistor width, respectively, as compared with existing methodologies. Similarly, data paths resized using the proposed methodology result in a significant performance improvement when compared with their conventionally designed counterparts.