Patent ID: 7589579

Claim:
A mixer circuit comprising: a first input stage that receives a first input voltage signal at a first frequency and generates a first output current varying in dependence upon said first input voltage signal, the first input stage comprising a first transistor and a second transistor connected to said first transistor, wherein the first input voltage signal is applied to bases of the first transistor and the second transistor; a second input stage that receives the first input voltage signal at the first frequency and generates a second output current varying in dependence upon the first input voltage signal, the second input stage comprising a third transistor and a fourth transistor connected to said third transistor, wherein the first input voltage signal is applied to bases of the third transistor and the fourth transistor; and a first current modulating stage connected to the first input stage to modulate the first output current, wherein the first current modulating stage comprises: a fifth transistor that receives a second input voltage signal at a second frequency, and a sixth transistor connected to said fifth transistor that receives a third input voltage signal, substantially 180 degrees out of phase with the second input voltage signal to superimpose a first modulating current signal, having substantially twice said second frequency, onto said first output current; and a second current modulating stage connected to the second input stage to modulate the second output current, wherein the second current modulating stage comprises: a seventh transistor that receives a fourth input voltage signal at a second frequency, and an eighth transistor connected to the seventh transistor that receives a fifth input voltage signal, substantially 180 degrees out of phase with the fourth input voltage signal to superimpose a second modulating current signal, having substantially twice said second frequency, onto the second output current.