Ring oscillator with calibration circuit for accurate on-chip IR-drop measurement

Resource estimation of power distribution network (PDN) is a critical issue for the resource management of LSIs. To evaluate the impact of PDN parameters to the quality of power distribution, an accurate PDN simulation model is necessary. To reflect the real silicon´s behavior to PDN simulation models, we propose a test structure that consists of an array of Ring Oscillators (ROs) with calibration circuits for static IR-drop measurement. The calibration circuit is used for the estimation of the RO frequency at no IR-drop condition so that we can estimate the absolute value of the IR-drop under operating condition. A test chip which includes 540 ROs and 270 calibration circuits is fabricated in a 65 nm process. The maximum discrepancy between the measurement and simulation values is 0.18 % in our experiment.