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This paper describes a new architecture that explores time-based signal-processing concepts for testing LC-tank radio-frequency (RF) oscillator circuits, and in particular, quadrature oscillators, while relying on low-frequency digital test equipment. The proposed system has two inputs that are two step-like signals with a time separation that is externally controlled. The output of the system is an amplified and digitized time separation that is a function of the time separation between the applied input steps and the oscillator output frequency characteristics. Coarse time digitization circuits are used to read the output, from which the frequency of oscillation of the oscillator is deduced. A proof-of-concept circuit is designed and fabricated in a standard 0.18-μm CMOS process. Experimental results confirm the feasibility of the proposed approach, which is demonstrated in this work with the successful on-chip measurement of 1.5 and 1.7 GHz oscillation frequencies.