A 2.6 mV/b Resolution, 1.2 GHz Throughput, All-Digital Voltage Droop Monitor Using Coupled Ring Oscillators in Intel 4 CMOS.

We present an all-digital voltage droop monitor (VDM) with coupled ring-oscillators (CoRO) for accurate in-situ droop monitoring every clock cycle. Measurements from a 3.2mm ² testchip in Intel 4 CMOS containing 9 3-way CoRO and baseline RO VDMs demonstrate 3X improvement in CoRO resolution $(\sim 2.6$ mV/b) over the baseline. In addition, measurements show $3 \sigma$ uncertainty (repeatability) error of CoRO VDM (+/-9mV) is $\sim25$ % lower than the baseline. The overall droop detection error improvements achieved by CoRO VDM are 12mV, 15mV and 17mV, respectively, depending on the type of calibration used - per instance/temperature/die, per temperature/die, or per die. This corresponds to associated IP power savings of 2.9%, 3.2% and 3.7% during functional use.