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A first-order linear model is formulated in closed-form for the examination of transient propagation through charge pump phase-locked loops (PLL). As a result, a novel PLL design parameter-the PLL critical time constant-is discovered as the primary factor influencing extraneous transient generation and propagation through the PLL independent of technology node. Various simulations and experiments have been performed on PLL circuits designed in 130 nm and 90 nm technology nodes. Using the described simulation and laser two-photon absorption (TPA) techniques, the generalized model is shown to accurately predict the output phase displacements and critical time constant of the PLL following transient perturbations, validating the analytical results independent of technology and without the need for calibration parameters. Moreover, the characteristic critical time constant is shown to be valuable for identifying and evaluating the single-event vulnerabilities in charge pump PLL designs.
Date of Publication: Oct. 2010