The design of monolithic differential VCOs

Techniques for the design of oscillators with two balanced outputs have been demonstrated, exploiting the concept of the virtual earth. This technique holds several advantages over the use of a single-ended oscillator and balun combination, namely: reduced size (particularly in monolithic implementation); symmetrical oscillator design guarantees outputs with 180° phase difference for driving balanced mixers; and the elimination of common-lead inductance problems. Furthermore, in monolithic technologies the use of virtual earths also yields the following advantages: via-free design is smaller, cheaper and higher yield; less parasitic inductance means higher possible frequencies of oscillation; less strays and parasitics results in higher Q (lower phase noise) oscillators; and less LO leakage to other sensitive areas of multi-function circuits