Patent ID: 7659784

Claim:
An injection-locked frequency divider, comprising: a voltage control oscillator (VCO) for generating a differential oscillation signal comprising a first oscillation signal and a second oscillation signal, the VCO comprising: an LC resonance tank, comprising a first connection terminal, a second connection terminal, and a third connection terminal, the third terminal receiving a reactance control signal for adjusting a reactance of the LC resonance tank and resonating to generate the differential oscillation signal, wherein the LC resonance tank outputs the first and second oscillation signals respectively from the first and second connection terminals; and a negative resistance generator, coupled to the first and second connection terminals, for eliminating an equivalent resistance generated by the LC resonance tank and maintaining the VCO to oscillate continuously; and a mixer, coupled to the VCO, comprising a first local input terminal and a second local input terminal respectively receiving a first injection signal and a second injection signal of a differential injection signal, and a first RF input terminal and a second RF input terminal receiving the first and second oscillation signals respectively, for mixing the differential signal with the differential oscillation signal, and thus adjusting and locking an output frequency of the differential oscillation signal, wherein the LC resonance tank comprises: a first capacitor, having a first terminal serving as the first connection terminal; a second capacitor, having a first terminal serving as the second connection terminal; a first inductance, having a first terminal coupled to a second terminal of the first capacitor; a second inductance, having a first terminal coupled to the first terminal of the first inductance, and a second terminal coupled to a bias voltage; a third inductance, having a first terminal coupled to the second terminal of the second inductance, and a second terminal coupled to a second terminal of the second capacitor; a fourth inductance, having a first terminal coupled to the second terminal of the third inductance; a first variable capacitor, having a first terminal coupled to a second terminal of the first inductance, and a second terminal receiving a reactance control signal; a second variable capacitor, having a first terminal coupled to the second terminal of the first variable capacitor, and a second terminal coupled to a second terminal of the fourth inductance; a first switch, having a first terminal coupled to the first terminal of the first capacitor, a second terminal coupled to a first voltage, and a control terminal coupled to the second terminal of the first inductance; and a second switch, having a first terminal coupled to the first terminal of the second capacitor, a second terminal coupled to the first voltage, and a control terminal coupled to the second terminal of the fourth inductance, wherein the LC resonance tank adjusts a reactance value according to the reactance control signal.