Taiwan Semiconductor Manufacturing Company Limited
Fractional realignment techniques for PLLs

Abstract:

Systems, methods, and devices for fractional realignment are disclosed herein. A feedback divider generates a feedback dividing clock signal based on a controlling oscillator frequency. A delta-sigma modulator is coupled to the feedback divider and generates a dividing ratio to the feedback divider. An accumulating phase adjustor is coupled to the delta-sigma modulator and (i) determines a difference between a frequency tuning word (FCW) and the dividing ratio and (ii) generates a coarse tuning word and a fine tuning word. A digital-to-time converter (DTC) is coupled to the accumulating phase adjustor and generates a first clock frequency based on a reference clock frequency, the coarse tuning word and the fine tuning word. A realignment pulse generator is coupled to the DTC and generates a realignment clock based on the first clock frequency having a period that is the same as a period of the controlling oscillator frequency.