US Patent 11070217 Phase locked loop circuit

Disclosed here is a PLL circuit that is an injection-locked PLL circuit. The PLL circuit includes a variable frequency oscillator configured in such a manner that a ring oscillator is formed during a period in which a window signal is negated and an injection edge based on a reference clock is allowed to be injected during a period in which the window signal is asserted, a feedback circuit that controls the variable frequency oscillator in such a manner that an oscillation frequency of the variable frequency oscillator gets closer to a target frequency according to the reference clock, and a window generator that receives an internal clock of the variable frequency oscillator and cuts out one pulse to generate the window signal.