Application of ring oscillators to characterize transmission lines in VLSI circuits

This paper presents a method that enables an estimation of the per-unit-length capacitance of transmission lines on VLSI CMOS chips with the help of ring oscillators. For the determination of the line capacitance four different ring oscillators possessing transmission lines of various lengths are implemented upon test chips for process characterization. A simple analytical model of the ring oscillator is developed and a formula derived that estimates the per-unit-length capacitance of the transmission lines out of the periods of oscillation of the ring oscillators. SPICE simulation results (E-SPICE as well as H-SPICE) using process parameters for a 1.5-/spl mu/m CMOS process are included. An experimental verification was also performed by implementing the ring oscillators on a test chip for a 0.8-/spl mu/m CMOS technology. The determined line parameters are valid for a frequency range up to about 500 MHz.<
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