Patent ID: 7705686

Claim:
An injection-locked frequency divider, comprising: a ring oscillator, which comprises a first delay cell and a second delay cell, wherein each of the first delay cell and the second delay cell comprises differential input terminals and differential output terminals and the differential input terminals and the differential output terminals of the first delay cell are respectively coupled to the differential output terminals and the differential input terminals of the second delay cell; a signal injection circuit for injecting a first injection signal and a second injection signal to the differential input terminals of the first delay cell and the differential input terminals of the second delay cell, respectively, wherein the first injection signal and the second injection signal are differential signals; and a first adjustable load circuit and a second adjustable load circuit, which are respectively connected between the differential output terminals of the first delay cell and connected between the differential output terminals of the second delay cell, change equivalent impedances of the first adjustable load circuit and the second adjustable load circuit, so as to change a free-running frequency of an oscillation signal of the ring oscillator in response to an adjustable voltage, and thus adjust an injection-locked frequency range of the injection-locked frequency divider, wherein the first adjustable load circuit comprises a first inductor, a second inductor and a first transistor, and the first transistor has a control terminal for receiving the adjustable voltage, a first terminal coupled to a first terminal of the differential output terminals of the first delay cell via the first inductor, and a second terminal coupled to a second terminal of the differential output terminals of the first delay cell via the second inductor; wherein the adjustable voltage is a continuously adjustable analog voltage; and wherein the first injection signal and the second injection signal are mixed with the oscillation signal so that a set of differential pair signals is outputted from the differential output terminals of each of the first and second delay cells, and a frequency of the set of differential pair signals is substantially equal to (I/N) times of a frequency of the first and second injection signals when the frequency of the first and second injection signals falls within an injection-locked frequency-divided range, which corresponds to N times of the free-running frequency, of the injection-locked frequency divider, wherein N is a natural number greater than 1.