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In this paper, the locking range of the injection-locked ring oscillators is investigated. To improve the injection efficiency and the locking range for superharmonic frequency division, a multiple-injection technique is proposed. Using a 0.18-mum CMOS process, a wideband frequency divider based on a three-stage ring oscillator is implemented for demonstration. With a tunable free-running frequency, the fabricated circuit provides 2:1 and 4:1 frequency division with a single-ended input signal ranging from 13 to 25 and 30 to 45 GHz, respectively. Compared with the case of the single-ended injection, the locking range of the frequency divider almost doubles when multiple-input injection with optimum phases is utilized. The experimental results exhibit good agreement with the theoretical derivation and the circuit simulation.
Date of Publication: Sept. 2007