Patent ID: 7710211

Claim:
An injection-locked frequency divider, comprising: a signal injection circuit, coupled to an injection signal source, injecting an injection signal; and a colpitts voltage controlled oscillator (VCO), comprising: a first transistor and a second transistor, each comprising a first terminal for receiving the injection signal and a second terminal coupled to an operational voltage; a first LC tank circuit and a second LC tank circuit, respectively disposed across a control terminal and the first terminal of the first transistor and the second transistor for determining a resonance frequency of an oscillation signal of the colpitts VCO; and a cross-coupled transistor pair, comprising a third transistor and a fourth transistor, wherein control terminals of the third transistor and the fourth transistor are respectively coupled to first terminals of the fourth transistor and the third transistor, the first terminals of the third transistor and the fourth transistor are respectively coupled to a first terminal or control terminal of the first transistor and the second transistor for providing an equivalent negative resistance to cancel a loss of parasitic equivalent resistance in the first LC tank circuit and the second LC tank circuit and outputting a pair of differential output signals at the first terminals of the third transistor and the fourth transistor; wherein the injection signal and the oscillation signal are mixed in frequency to generate the pair of differential output signals, the signal injection circuit further locking the pair of differential output signals.