Patent ID: 8035457

Claim:
A voltage controlled oscillator (VCO), comprising: a first voltage controlled current source (VCCS) having a control end and a current end, wherein the control end receives a control voltage; a first negative resistance circuit (NRC) having a first current path and a second current path, wherein first ends of the first and the second current paths are coupled to the current end of the first VCCS; a first transformer having a primary side and a secondary side, wherein the primary side of the first transformer is coupled to a second end of the first current path of the first NRC, and the secondary side of the first transformer serves as a first output end of the VCO; a second transformer having a primary side and a secondary side, wherein the primary side of the second transformer is coupled to a second end of the second current path of the first NRC, and the secondary side of the second transformer serves as a second output end of the VCO; a first transistor having a first end coupled to the secondary side of the first transformer, and a control end coupled to the primary side of the first transformer; and a second transistor having a first end coupled to the secondary side of the second transformer, and a control end coupled to the primary side of the second transformer; and a second VCCS having a control end and a current end, wherein the control end receives a second control voltage; and a second NRC having a first current path and a second current path, wherein first ends of the first and the second current paths of the second NRC are coupled to the current end of the second VCCS, and second ends of the first and the second current paths of the second NRC are respectively coupled to the primary sides of the first and the second transformers; and a bias voltage generating unit coupled to the control ends of the first and the second VCCs and configured to provide the control voltage and the second control voltage.